TNITEB8ITY OF CALIFORNIA PUBLICATIONS 
 
 COLLEGE OF AGRICULTURE 
 
 AGRICULTURAL EXPERIMENT STATION 
 
 BERKELEY, CALIFORNIA 
 
 WALNUT CULTURE 
 IN CALIFORNIA 
 
 BY 
 
 L. D. BATCHELOR 
 
 BULLETIN No. 332 
 
 June, 1921 
 
 UNIVERSITY OF CALIFORNIA PRESS 
 
 BERKELEY. CALIFORNIA 
 
 1921 
 
David P. Barrows, President of the University. 
 
 EXPERIMENT STATION STAFF 
 
 HEADS OF DIVISIONS 
 
 Thomas Forsyth Hunt, Dean. 
 
 Edward J. Wickson, Horticulture (Emeritus). 
 
 Walter Mulford, Forestry, Director of Resident Instruction. 
 
 C. M. Haring, Veterinary Science, Director of Agricultural Experiment Station. 
 
 B. H. Crocheron, Director of Agricultural Extension. 
 Hubert E. Van Norman, Vice-Director; Dairy Management. 
 
 James T. Barrett, Plant Pathology, Acting Director of Citrus Experiment Station. 
 William A. Setchell, Botany. 
 Myer E. Jaffa, Nutrition. 
 Ralph E. Smith, Plant Pathology. 
 John W. Gilmore, Agronomy. 
 Charles F. Shaw, Soil Technology. 
 
 John W. Gregg, Landscape Gardening and Floriculture. 
 Frederic T. Bioletti, Viticulture and Fruit Products. 
 Warren T. Clarke, Agricultural Extension. 
 John S. Burd, Agricultural Chemistry. 
 Charles B. Lipman, Soil Chemistry and Bacteriology. 
 Ernest B. Babcock, Genetics. 
 Gordon H. True, Animal Husbandry. 
 Fritz W. Woll, Animal Nutrition. 
 W. P. Kelley, Agricultural Chemistry. 
 H. J. Quayle, Entomology. 
 Elwood Mead, Rural Institutions. 
 H. S. Reed, Plant Physiology. 
 L. D. Batchelor, Orchard Management. 
 J. C. Whitten, Pomology. 
 *Frank Adams, Irrigation Investigations. 
 
 C. L. Roadhouse, Dairy Industry. 
 R. L. Adams, Farm Management. 
 
 F. L. Griffin, Agricultural Education. 
 John E. Dougherty, Poultry Husbandry. 
 W. B. Herms, Entomology and Parasitology. 
 L. J. Fletcher, Agricultural Engineering. 
 Edwin C. Voorhies, Assistant to the Dean. 
 
 Citrus Experiment Station Staff 
 
 J. T. Barrett, Acting Dean and Director. 
 
 W. P. Kelley, Professor of Agricultural Chemistry. 
 
 H. J. Quayle, Professor of Entomology. 
 
 H. S. Reed, Professor of Plant Physiology. 
 
 L. D. Batchelor, Professor of Orchard Management. 
 
 H. S. Fawcett, Professor of Plant Pathology. 
 
 R. S. Vaile, Assistant Professor of Orchard Management. 
 
 A. R. C. Haas, Assistant Professor of Plant Pathology. 
 
 E. T. Bartholomew, Assistant Professor of Plant Pathology. 
 
 C. O. Smith, Research Associate in Plant Pathology. 
 
 E. E. Thomas, Research Associate in Agricultural Chemistry. 
 H. B. Frost, Research Associate in Plant Breeding. 
 
 F. F. Halma, Research Associate in Plant Physiology. 
 J. G. Surr, Assistant in Orchard Management. 
 Hugh Knight, Assistant in Entomology. 
 
 S. M. Brown, Assistant in Chemistry. 
 
 A. B. Cummins, Assistant in Agricultural Chemistry. 
 
 * In cooperation with office of Public Roads and Rural Engineering, U. S. Department of 
 Agriculture. 
 
WALNUT CULTURE IN CALIFORNIA 1 
 
 By L. D. BATCHELOR 
 
 CONTENTS 
 
 PAGE 
 
 General Review of the Walnut Industry 142 
 
 Business prospects of the industry 143 
 
 Length of life of walnut trees 143 
 
 Profitable bearing of young trees 145 
 
 Climatic Requirements 146 
 
 Frost injury 146 
 
 Heat injury 147 
 
 Soil Requirements 148 
 
 Depth and character of soil 148 
 
 Drainage and alkali injury 149 
 
 Water Supply........ 150 
 
 Amount of irrigation water necessary 150 
 
 Rainfall in walnut-growing sections 151 
 
 Irrigation water of good quality essential 152 
 
 Varieties 153 
 
 Description of varieties 155 
 
 Placentia 155 
 
 Eureka 156 
 
 Ehrhardt 159 
 
 Payne ' 162 
 
 Concord 162 
 
 Franquette 164 
 
 Rootstocks and Choice of Nursery Trees 165 
 
 Choice of rootstock 165 
 
 Method of propagation 166 
 
 Requirements for good nursery trees 166 
 
 Starting the Young Orchard 166 
 
 Laying out the orchard 166 
 
 Care of trees before planting 168 
 
 Planting the young orchard ' 170 
 
 Training young trees 170 
 
 Values of orchards and lands 175 
 
 Culture : 176 
 
 Soil management 176 
 
 Covercropping 180 
 
 Irrigation 186 
 
 Intercropping 196 
 
 Fertilization 201 
 
 Pruning 202 
 
 Insects and Disease Pests 203 
 
 Codling moth and aphis 203 
 
 Red spider 204 
 
 Walnut blight 205 
 
 Melaxuma 206 
 
 Winter-injury or Die-back 208 
 
 Harvesting, Curing, Packing and Cost of Production 210 
 
 Harvesting 210 
 
 Washing and curing 212 
 
 Packing 214 
 
 The standard for first-grade nuts 216 
 
 Selling the crop 216 
 
 Income to be derived from California walnuts 217 
 
 i Paper No. 82, University of California, Graduate School of Tropical Agricul- 
 ture and Citrus Experiment Station, Riverside, California. 
 
142 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 
 
 PREFACE 
 
 The present bulletin represents the results of general observations 
 and specific investigations of the writer and his associates. The 
 subject matter and the method of presentation have been chosen in 
 response to the numerous inquiries relating to general walnut culture, 
 which have been received during the past six years. 
 
 The writers' thanks are extended to Mr. Carlyle Thorpe, Professor 
 F. T. Bioletti, and Dr. H. S. Reed for their careful criticism of the 
 manuscript, and to Mr. D. C. Wylie, of the California Walnut 
 Growers' Association, for his able assistance in gathering much of 
 the general information in the walnut groves and among the walnut 
 growers in various parts of California. Use has been made of the 
 Experiment Station Bulletin 231, by Professor Ralph Smith, and of 
 "The California Walnut," by Mr. W. T. Webber and Mr. W. E. 
 Goodspeed. 
 
 For a more detailed discussion of the several ramifications of this 
 subject, such as history, nursery propagation, and the description of 
 rarely found varieties and diseases, the reader is referred to Smith, 
 R. E., Walnut Culture in California, Univ. of Calif. Bull. 231, 1912, 
 and also to Lake, E. R., The Persian Walnut Industry of the United 
 States, U. S. Dept. of Agr., Bur. Plant Ind., Bull. 254, 1913. 
 
 GENERAL REVIEW OF THE WALNUT INDUSTRY 
 
 The Persian walnut (Juglmis regia) or, as it is more commonly 
 known, the English walnut, may be seen growing in nearly every 
 county in the state of California. The commercial production of nuts, 
 however, is centered mainly in southern California in the following 
 four counties, mentioned in the order of importance : Los Angeles, 
 Orange, Ventura, and Santa Barbara. Riverside and San Bernar- 
 dino counties have a considerable area of young groves; and in the 
 central part of the state walnut culture is gradually becoming im- 
 portant in the following counties : Santa Clara, San Joaquin, Contra 
 Costa, Napa, and Sonoma. 
 
 Figure 1 shows a map of the state and the relative importance 
 and distribution of the crop in the several counties. 
 
 At the present writing, there are approximately 85,000 acres of 
 walnut trees of various ages within the state. The annual production 
 for the state during the last ten years may be seen from the following 
 table : 
 
Bulletin 332] WALNUT CULTURE IN CALIFORNIA 143 
 
 TABLE I 
 
 Annual Production of Walnuts in California 
 (Expressed in pounds) 
 
 1911 25,000,000 1916 29,200,000 
 
 1912 22,500,000 1917 33,000,000 
 
 1913 22,700,000 1918 40,231,000 
 
 1914 17,800,000 1919 56,200,000 
 
 1915 29,650,000 1920 43,000,000 
 
 BUSINESS PROSPECTS OF THE INDUSTRY 
 
 The present condition of the industry indicates that walnuts may 
 continue to be one of the most staple and at the same time most profit- 
 able crops which can be grown on land, and in locations, adapted to 
 this crop. The annual consumption of walnuts in the United States 
 has ranged between 60,000,000 and 70,000,000 pounds annually during 
 the past five years, and has increased more than 30 per cent since 
 1909. Nuts, which were formerly looked upon as a holiday luxury, 
 are becoming more and more a food to be used the year through in the 
 average household. This increase and wider use of the walnut has 
 been accompanied by an increase in importation exceeding our own 
 average production, and a gradual increase in the prices paid to the 
 California grower. It may thus be inferred that the business of wal- 
 nut culture in California is not likely to suffer from the results of 
 over-production in the near future. It is difficult to forecast future 
 economic conditions relating to the production and sale of any par- 
 ticular crop. Nevertheless, many of the older walnut growers, who 
 have known this industry from its early days, believe that the planting 
 of a walnut grove at present is as safe an investment as it has been at 
 any time during the development of the industry. 
 
 LENGTH OF LIFE OF WALNUT TREES 
 
 The limit of the profitable length of life of a walnut grove cannot 
 be told from experiences in California. Provided the soil, climatic, 
 and water conditions are well suited to this crop, the trees may con- 
 tinue to thrive and produce satisfactory crops for a long period, which 
 is difficult to limit. Some observers have expressed opinions that 
 walnut groves, under favorable conditions, may continue to be a satis- 
 factory source of revenue until the trees are from 50 to 200 years old. 
 Some of the oldest walnut groves in Ventura County are the most 
 profitable and productive in the state. Notable examples of such old, 
 yet productive groves, are the J. C. Daly grove of 20 acres planted 
 in 1881 ; 18 acres of the J. M. Sharp grove planted in 1887 ; and the 
 
144 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 T. A. Kelsey grove of 26 acres planted in 1888. The last mentioned 
 grove has only 12 trees to the acre, planted 60 feet apart each way, 
 and is considered by many to be one of the best walnut properties in 
 the state of California. The trees, at their present age of 34 years, 
 
 Fig. 1. (From < ' The California Walnut. ") 
 
 show no apparent deterioration. This grove has produced an average 
 annual tonnage of 1941 pounds of nuts per acre during the past four 
 years. Groves in which the trees are planted 60 feet each way may 
 be expected to grow longer without deterioration than groves where 
 the trees are planted closer and thus severely compete with each other. 
 
BULLETIN 332] WALNUT CULTURE IN CALIFORNIA 145 
 
 PROFITABLE BEARING OF YOUNG TREES 
 
 The young walnut grove may be expected to bear profitable crops 
 by the time the trees are 6 to 10 years old, depending upon the variety, 
 the number of trees planted per acre, and the natural conditions 
 surrounding the grove. 
 
 A grove of almost 50 acres of the Placentia variety in Orange 
 County produced an average of 44 pounds of ungraded nuts per tree 
 in its ninth year. As the trees are 60 feet apart this represents 528 
 pounds per acre. During the first 10 or 12 years this might well have 
 been double planted and thus produced approximately 1056 pounds 
 per acre the ninth year. 
 
 In 1918 a block of 60 trees of the Chase variety, on a heavy clay 
 loam soil in the Puente district, produced a profitable crop of 35 
 pounds per tree in the sixth year. The records of these groves and 
 of a grove of 38 Ehrhardt trees are shown in Table II. 
 
 In considering this table one should keep in mind that each of these 
 plantations is growing under the best natural and cultural conditions, 
 and is thus without doubt considerably above the average. In pro- 
 jecting a business enterprise, the yields shown may be looked upon 
 as approaching the maximum possibilities and should therefore be 
 discounted 25 to 50 per cent to reach a figure which may reasonably 
 be expected to prevail under average conditions. Again, the figures 
 here presented are of little value in making comparisons between the 
 three varieties in question, as no two varieties were of the same age 
 the same season. 
 
 TABLE II 
 
 Average Yearly Production per Tree of Young "Walnut Groves 
 
 Variety 
 
 
 r 
 Placent 
 
 A 
 
 ia 
 
 Chase 
 
 
 Ehrhs 
 
 irdt 
 
 Year 
 
 r 
 
 Season's 
 growth 
 
 
 Yield 
 in lbs. 
 
 Season's Yield 
 
 growth in lbs. 
 
 (Ungraded nuts 
 
 at harvest) 
 
 r y 
 Season's Yield 
 growth in lbs. 
 (Ungraded nuts 
 at harvest) 
 
 1915 
 
 7th 
 
 
 22f 
 
 
 
 
 
 10th 
 
 80 
 
 1916 
 
 8th 
 
 
 27f 
 
 .... 
 
 .... 
 
 11th 
 
 76 
 
 1917 
 
 9th 
 
 
 44* 
 
 5th 
 
 18 
 
 12th 
 
 79 
 
 1918 
 
 10th 
 
 
 43* 
 
 6th 
 
 35 
 
 13th 
 
 81 
 
 1919 
 
 11th 
 
 
 104* 
 
 7th 
 
 72 
 
 14th 
 
 117 
 
 1920 
 
 12th 
 
 
 82* 
 
 8th 
 
 43 
 
 15th 
 
 98 
 
 * Pounds of uncured and ungraded nuts at harvest, 
 t Pounds of cured and ungraded nuts at harvest. 
 
146 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 Although the cultural and natural conditions in all these groves 
 were favorable, the plantings are several miles apart and conditions 
 were not identical. Certain seasons are particularly favorable to crop 
 production. The year 1919 was characterized by especially abundant 
 crops of walnuts. These were followed in many cases by lighter crops 
 in 1920, although the young trees were one year older and had a 
 greater bearing surface. 
 
 CLIMATIC REQUIREMENTS 
 
 The chief climatic limitations of the walnut are frosts in spring 
 and fall, and extreme heat in summer. 
 
 FROST INJURY 
 
 Low frosty sites should be avoided for walnuts. A temperature 
 of even 2 or 3 degrees below freezing (32° F.) will usually kill a large 
 percentage of the young walnut flowers, if they are just starting to 
 bloom. During the season of 1920, late spring frosts during the second 
 week of April reduced the walnut crop to a great extent in several 
 of the inland valleys. In one instance at least, the absolute minimum 
 recorded by a reliable thermometer was only 29° F., yet it was esti- 
 mated that 50 per cent of the crop was destroyed. During this period 
 apricots and the earlier blooming cling peaches in adjacent orchards, 
 were about the size of green peas, and experienced little or no injury. 
 
 During the morning of April 6, 1921, a minimum temperature of 
 27° F. was experienced by a seedling walnut grove in which the 
 majority of the trees were in full bloom. This temperature prevailed 
 for about an hour and apparently destroyed nearly the whole potential 
 crop, except in the tops and centers of the trees, where an occasional 
 cluster of blooms escaped injury. 
 
 As a general rule, the late blooming varieties, such as the Eureka 
 and Concord, may be expected to escape injury from the late spring 
 frost more consistently than the earlier blooming soft-shell types. 
 During the spring of 1915, however, walnut twig tips and young nuts 
 were killed during the first week in May on some of the low sites in 
 Los Angeles County. With a frost as late as May the late blooming 
 varieties may suffer more. injury than the earlier ones, as the young 
 nuts (one half -inch or more in diameter) of the early blooming varie- 
 ties, at this time, will stand more cold than the blossoms of the late 
 varieties. The late bloomer does not, therefore, always escape late 
 spring frosts. It is much better to avoid planting walnuts on land 
 which is considered too frosty for peaches during the majority of 
 
Bulletin 332] WALNUT CULTURE IN CALIFORNIA 147 
 
 seasons. The varieties of the soft-shell type bloom about the same 
 time as the Bartlett pear and are not nearly so resistant to frost 
 injury of the blooms. 
 
 Early fall frosts also cause injury, especially to young shoot 
 growth ; though this injury may not be apparent to the casual observer 
 until the following spring, when the tree fails to leaf out on the major 
 portion of the past season's growth. This type of injury is more fully 
 treated under the subject of die-back. It may suffice to explain here 
 that early fall frosts prematurely stop the final ripening process of the 
 twigs by killing the leaves. Such injured leaves will usually fall off 
 within a week after the frost injury, whereas they might otherwise 
 have functioned normally a month or six weeks longer. The bare, 
 immature twigs dry out rapidly and sunburn on the south side during 
 the winter months, killing back several inches, or possibly several feet 
 to the more mature wood, which has been able to withstand the 
 abnormal insolation. 
 
 HEAT INJURY 
 
 The chief injury to the walnuts during the extreme hot weather 
 of the summer months is the sunburning of nuts on the outsides, tops, 
 and south sides of the trees. Such burned nuts usually become 
 "blanks" if the injury occurs during June or July. If the sunburn- 
 ing takes place when the nuts are more fully developed, in August, 
 they may be salvaged as culls with a portion of the kernels edible. In 
 mild cases of sunburn injury, a small part of the husk may stick to 
 the shell or may only stain it, causing the nut to be graded out as a 
 cull. The kernels of such nuts may be of first quality, although it is 
 likely that there will occur a high percentage of amber and black 
 kernels and partly shriveled and mouldy meats among this class of 
 nuts. Nuts on trees growing on a deep silt soil withstand the extreme 
 heat without burning much better than nuts on trees growing on a 
 shallow soil with less moisture available. Sandy soils must be fre- 
 quently irrigated in the hot sections if the walnuts, are to avoid serious 
 injury by sunburning. At a maximum temperature of 100° F. in the 
 shade, accompanied by low humidity, walnuts which are exposed to 
 the direct rays of the sun may be expected to sunburn. This tempera- 
 ture, or higher, occurs in many of the inland valleys, 15 to 30 days 
 during the summer months. Under such conditions the crop is always 
 injured by sunburn. Regardless of this, the planting of walnuts is 
 extending more and more inland. The planting of oranges is restrain- 
 ing the development of walnut groves on the coastal sections. At the 
 present time walnut groves have not become as productive in the 
 
148 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 
 
 inland valleys, which experience frequent summer days with maximum 
 temperatures of 100° F. and over, as they have been nearer the coast, 
 where the weather is characterized by a smaller daily range and a 
 lower maximum temperature. Varieties especially selected for the 
 hotter sections may tend to correct this difficulty in the future. In the 
 past, most of the walnuts planted inland have been of the same varie- 
 ties as those which were originally selected for the coastal regions. 
 Varietal adaptation is more fully treated under the heading of 
 varieties. 
 
 At present walnut culture is most successful in the sections of the 
 state which are characterized by a long growing season free from 
 frosts, where the daily range in temperature is not great, where the 
 absolute maximum seldom goes above 100° F., and where winter tem- 
 peratures are moderate and the humidity is high, especially during 
 the summer. Sudden changes in temperature, such as occur in the 
 desert regions, seem decidedly detrimental to the growth of the walnut 
 tree. The localities where favorable climatic conditions occur is indi- 
 cated by the fact that the largest walnut shipping centers in the state 
 are Santa Ana, Whittier, Puente, Saticoy, and Santa Barbara. 
 
 When the tree is fully dormant, the absolute minimum tempera- 
 tures of winter, during January and February, apparently have very 
 little to do with its welfare. This is especially true of the French 
 varieties. Trees of the Mayette and Franquette varieties have grown 
 for some years without severe winter injury along the west side of 
 the Wasatch Mountains north of Salt Lake City, Utah, where the 
 minimum temperature occasionally was 5° below zero (Fahrenheit) 
 during the winters of 1913-14 and 1914-15. 
 
 SOIL REQUIREMENTS 
 
 DEPTH AND CHARACTER OF SOIL 
 
 The success of walnut culture is dependent upon favorable soil 
 conditions to a greater extent than that of many other tree crops. A 
 well-drained deep silt loam, containing an abundance of organic 
 matter, free from a high or fluctuating water table, hardpan, sandy 
 subsoil, and ' ' alkali, ' ' is essential for a first-class walnut grove. Shal- 
 low soils underlaid by a hardpan or an impervious clay stratum within 
 5 or 6 feet from the surface will produce only a short-lived, second- 
 rate walnut grove. Such groves are frequently stunted in growth, 
 subject to yellowness, and are poor producers. 
 
 There are a few moderately successful groves growing in fine silt 
 soil underlaid with fine sand within 4 or 5 feet from the surface, 
 but such properties require the greatest skill in planning the cultural 
 
Bulletin 332] WALNUT CULTURE IN CALIFORNIA 149 
 
 and irrigation practice and should certainly be avoided by the beginner 
 in walnut growing. 
 
 Very light sandy soils are usually unsatisfactory, producing slow- 
 growing, stunted, poor-yielding trees. On such soils the nuts are 
 very subject to sunburning. One should not judge the soil conditions 
 entirely by the surface soil. The nature of the subsoil may be of great 
 importance. There are first-class walnut groves in the El Monte 
 district growing, apparently, in a very light sandy soil. The soil 
 changes, however, in some instances 3 or 4 feet from the surface, 
 grading into a silt loam which seems to be an ideal soil for walnut 
 roots. 
 
 Very heavy adobe soils or silts underlaid by adobe are not best 
 suited to walnut groves. The trees on such soils are usually stunted, 
 making very little growth and fruit wood in the tops when mature. 
 These soils are difficult to cultivate, and it is difficult to obtain a deep 
 penetration of the irrigation water which is so essential to good walnut 
 culture. Such soils frequently contain amounts of alkali harmful to 
 walnuts, and their leaching by any system of irrigation is very difficult. 
 
 DRAINAGE AND ALKALI INJUEY 
 
 A water table within 9 or 10 feet from the surface of the soil 
 may make it impossible to maintain a profitable walnut grove. Most 
 of the high water tables in arid regions are characterized by carrying 
 more or less "alkali" 2 in solution. The mere presence of water within 
 9 or 10 feet of the surface is usually only part of the difficulty, 
 the alkali present is the greatest concern, for the deep-rooted trees 
 obtain a portion of their water from this water table and may be 
 injured by the salts therein, even though there is a seemingly sufficient 
 layer of good soil above the water. There occurs an instance in 
 Orange County where an old grove has been practically ruined by 
 a rise in the water table to within only nine feet of the surface. This 
 water contains 700 parts per million of salts. The water rises approxi- 
 mately 6 feet by capillary action in the soil; thus there is only a 
 3-foot depth, or one-third of the soil, above the standing water, which 
 is not impregnated with salts. Several instances were noted in Ven- 
 tura County during the fall of 1919 where walnut trees were severely 
 injured by the presence of an "alkali" ground water 9 to 13 feet 
 from the surface. When the trees were planted 20 years ago in this 
 district, the water was at least 30 feet from the surface. It is difficult 
 to place a definite safe boundary beyond which injury from a high 
 
 2 For a discussion of alkali in the irrigation water see page 152. 
 
150 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 water table is likely to occur. Apparently quite as much depends 
 upon the nature of the water as upon the actual depth from the 
 surface, within the limitation of the root zone. The rainfall, irrigation 
 practice, and nature of the soil, and the irrigation water may also 
 greatly influence the limitations, for walnut culture, of land with a 
 high water table. 
 
 Rarely there is found an exception to the rule of injury resulting 
 from a high water table. There is one notable example in Santa 
 Barbara County where an orchard is sub-irrirgated by a natural flow 
 of water from the hills. Judging from the appearance of the trees,* 
 this ground water contains no (or an exceedingly small amount of) 
 "alkali," a condition which is exceptional to the usual shallow water 
 tables in irrigated areas of the arid west. 
 
 WATER SUPPLY 
 
 In most of the California walnut districts, irrigation is necessary. 
 The amount of water to be applied and the seasons of application 
 naturally depend upon the rainfall, the amount of evaporation, the 
 nature of the soil, and other factors. The walnut tree can not be 
 expected to yield profitable crops unless furnished with an abundant 
 supply of water during the entire year. 
 
 AMOUNT OF IRRIGATION WATER NECESSARY 
 
 From 12 to 24 acre-inches per acre 3 of irrigation water is usually 
 applied to bearing walnut groves, varying according to some of the 
 conditions related in the preceding and the following paragraphs. 
 
 3 For those not familiar with the various methods of measuring water, the fol- 
 lowing explanation and table is offered converting miners' inches to acre inches. 
 An acre inch of water is the quantity of water required to cover one acre to a 
 depth of one inch. 
 
 50 California "miners' inches" = 1 cubic foot per second. 
 
 1 cubic foot per second = 7.48 gallons per second. 
 
 Table 
 Miners' inches to acre inches. 
 
 
 
 
 
 
 Miners 
 
 ' Inches 
 
 
 
 
 
 
 Hrs. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 
 1 
 
 .0198 
 
 .0396 
 
 .0594 
 
 .0792 
 
 .0990 
 
 .1188 
 
 .1386 
 
 .1584 
 
 .1782 
 
 .1980 
 
 
 2 
 
 .0396 
 
 .0792 
 
 .1188 
 
 .1584 
 
 .1980 
 
 .2376 
 
 .2772 
 
 .3168 
 
 .3564 
 
 .3960 
 
 
 3 
 
 .0594 
 
 .1188 
 
 .1782 
 
 .2376 
 
 .2970 
 
 .3564 
 
 .4158 
 
 .4752 
 
 .5346 
 
 .5940 
 
 
 4 
 
 .0792 
 
 .1584 
 
 .2376 
 
 •.3168 
 
 .3960 
 
 .4752 
 
 .5544 
 
 .6336 
 
 .7128 
 
 .7920 
 
 
 5 
 
 .0990 
 
 .1980 
 
 .2970 
 
 .3960 
 
 .4950 
 
 .5940 
 
 .6930 
 
 .7920 
 
 .8910 
 
 .9900 
 
 •s 
 
 PI 
 
 6 
 
 .1188 
 
 .2376 
 
 .3564 
 
 .4752 
 
 .5940 
 
 .7128 
 
 .8316 
 
 .9504 
 
 1.0892 
 
 1.1880 
 
 7 
 
 .1385 
 
 .2772 
 
 .4158 
 
 .5544 
 
 .6930 
 
 .8316 
 
 .9702 
 
 1.1088 
 
 1.2474 
 
 1.3860 
 
 <v 
 
 8 
 
 .1584 
 
 .3168 
 
 .4752 
 
 .6336 
 
 .7920 
 
 .9504 
 
 1.1088 
 
 1.2872 
 
 1.4256 
 
 1.5840 
 
 2 
 
 9 
 
 .1782 
 
 .3564 
 
 .5346 
 
 .7128 
 
 .8910 
 
 1.0692 
 
 1.2474 
 
 1.4256 
 
 1.6038 
 
 1.7820 
 
 < 
 
 10 
 
 .1980 
 
 .3980 
 
 .5940 
 
 .7920 
 
 .9900 
 
 1.1880 
 
 1.3860 
 
 1.5840 
 
 1.7820 
 
 1.9800 
 
 
 11 
 
 .2178 
 
 .4356 
 
 .6534 
 
 .8712 
 
 1.0890 
 
 1.3038 
 
 1.5246 
 
 1.7424 
 
 1.9602 
 
 2.1780 
 
 
 12 
 
 .2376 
 
 .4752 
 
 .7128 
 
 .9504 
 
 1.1880 
 
 1.4256 
 
 1.6632 
 
 1.9008 
 
 2.1384 
 
 2.3760 
 
 
BULLETIN 332] WALNUT CULTURE IN CALIFORNIA 151 
 
 The amount will vary with the nature of the soil, as an open sandy 
 soil requires more water to produce equivalent crops than a compact 
 silt loam. Closely planted and old bearing groves will require more 
 water than young groves or those with fewer trees to the acre, other 
 things being equal. 
 
 The rainfall varies from season to season and in some years it may 
 be necessary to apply 50 per cent more water than in others. There 
 is considerable variation in the average rainfall of the different dis- 
 tricts. A soil in Santa Barbara County might be thoroughly moist- 
 ened at the beginning of the growing season, owing to the previous 
 winter rains, to a depth of 8 or 10 feet, while a similar soil in Riverside 
 or in San Diego County might be wet to a depth of only 3 feet. 
 Obviously, the irrigation requirements of the following season would 
 be quite different in the two cases. Table III shows the average rain- 
 fall in several of the sections where walnuts are grown. 
 
 TABLE III 
 Showing the Normal Rainfall in Several Walnut Growing Sections 
 
 Normal annual 
 Place of rainfall in 
 
 observation inches 
 
 Los Angeles 14.6 
 
 Napa 24.3 
 
 Pomona* 19.2 
 
 Riverside 10.6 
 
 Santa Barbara 17.1 
 
 San Diego 10.0 
 
 San Jose 16.8 
 
 Santa Ana (Irvine) 13.3 
 
 Santa Rosa 32.0 
 
 Stockton 14.6 
 
 While the amount of seasonal rainfall may be taken as a good indi- 
 cation of the amount of irrigation water necessary to supplement it, 
 it should be borne in mind that other factors, such as frequency, dura- 
 tion, amount of individual rains, run-off, and season of occurrence, 
 must also be considered, as they influence the proportion of the total 
 precipitation which penetrates into the soil and is available to the 
 walnut trees. 
 
 The water requirements are higher in the warm inland valleys, with 
 their very low humidity and high temperatures during the growing 
 season, than in the coastal regions, with their cooler summers and 
 many foggy days. 
 
 Average of 8 years, 1913 to 1920 inclusive. 
 
152 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 It may be said, therefore, that the walnut grower in some of the 
 southern and central inland districts should be provided with a water 
 right of 24 acre inches per acre per year, and that from this maximum 
 the requirements diminish until in some individual and exceptional 
 cases in Santa Barbara, Santa Rosa, and Napa counties walnuts may 
 be grown successfully without any irrigation. 
 
 IRRIGATION WATER OF GOOD QUALITY ESSENTIAL 
 
 The quality of the irrigation water for walnuts is as essential as 
 the quantity. Relatively small amounts of the "alkali" salts carried 
 in the water are decidedly harmful to walnut trees. From many 
 observations made during the past five years, it seems that the walnut 
 tree is the most sensitive to alkali injury of all the orchard trees grown 
 in California. The minimum amount of salts which will prove toxic 
 to walnut trees will depend upon so many factors, such as the nature 
 of the soil, the under-drainage, the rainfall,' etc., that it may be im- 
 possible to state the exact maximum amount of salt which might be 
 applied with the water without injury. In the districts of heavy 
 rainfall and in well under-drained groves, water of poor quality could 
 no doubt be used longer without harm to the trees than in the more 
 arid regions, especially where hardpan exists. It is definitely known 
 that walnut groves have been injured severely by the use of irrigation 
 water containing only 340 parts per million of one or more of the 
 so-called "alkali" salts. 4 
 
 The particular salts which the water contains may have as great 
 a bearing on the injury as the type of soil and other natural conditions 
 of the orchard. It is impracticable to include a prolonged discussion 
 of the effect of alkali on walnuts in this publication ; suffice it to warn 
 the present or prospective walnut grower of the importance of a water 
 supply of good quality before continuing or establishing a walnut 
 plantation. It is especially important in projecting new plantings 
 to have the prospective water supply analyzed 5 and an expert opinion 
 given upon its suitability, before proceeding to develop the property. 
 
 4 For a discussion of alkali salts in irrigation water, see Kelley and Thomas, 
 ' ' The Effects of Alkali on Citrus Trees, ' J Univ. of Calif. Experiment Station Bull. 
 No. 318, 1920. 
 
 5 The University, through its division of Plant Nutrition at Berkeley or the 
 chemical division of the Citrus Experiment Station at Riverside, is prepared to 
 analyze irrigation waters free of charge, and give an opinion on their suitability 
 for irrigation purposes. 
 
Bulletin 332] 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 153 
 
 VARIETIES 
 
 The original walnut plantings in California were "hard-shell" and 
 "paper-shell" seedlings. From these early plantings, the next gene- 
 ration of nuts produced a nut commonly known as the Santa Barbara 
 soft-shell. The vast majority of the seedling walnut groves now grow- 
 ing in California consist of this variety. 
 
 From these latter seedlings many superior trees have been noted 
 during the past 15 or 20 years. From some of these, through propaga- 
 tion by grafting and budding, (in a way similar to. that of the orig- 
 ination of standard varieties of fruits, such as peaches, apples, 
 
 Fig. 2. — Effect of application of alkali water. Grove on left used water of 
 high salt content, that on right, good water. 
 
 oranges, etc.), new varieties of walnuts have arisen. The varieties 
 which trace back to the class of seedlings just discussed comprise the 
 vast majority of the sorts now planted in southern California, with 
 the exception of the Eureka variety, a brief history of which is given 
 under the description of this variety. Some of the walnut varieties 
 commonly planted in central California, such as the Concord, Fran- 
 quette, and Mayette, have still another origin, which will be discussed 
 under the heading of each respective variety. 
 
 The varieties of walnuts chosen for planting in California should 
 be those most marketable, most productive, and best adapted for 
 growing under the local conditions in question. At present, there are 
 comparatively few varieties which have won and retained their popu- 
 larity with the growers and the marketing trade. Many new varieties 
 
154 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 have been originated in California- during the past twenty years, but 
 most of them have been propagated only in a very limited way, and 
 have soon fallen into disfavor, owing to some particular shortcoming. 
 New varieties of the future should be a decided improvement upon 
 our present sorts; otherwise they are not worthy of even limited 
 propagation. 
 
 The principal economic advantages which a grafted or budded 
 grove of the best varieties possesses, in comparison with a seedling 
 walnut grove, are (.a) the budded nuts sell for a higher price than the 
 seedlings; 6 (6) a grafted grove is more uniform and has fewer unpro- 
 ductive trees than a seedling grove; and (c) the seedlings are more 
 susceptible to blight than are certain varieties* which are budded or 
 grafted. 
 
 There probably is no one best walnut variety for planting in the 
 whole state of California. With the varying soil and climatic condi- 
 tions, the success or failure of a variety may depend upon the question 
 of its adaptation to the specific conditions. In reading the discussion 
 of the varieties in the following pages and the recommendations which 
 are made for planting in the several localities, it should be borne in 
 mind that the observations concerning the varieties have been very 
 general. In many instances an attempt has been made to present the 
 consensus of the opinions of several observers, such as walnut growers, 
 packing-house experts, and nursery men, and, although the varieties 
 described seem to be the best for commercial planting at the present 
 time, they may be supplanted in the future by varieties entirely 
 unknown at present, or by varieties which may not be highly thought 
 of at this date. The selection of varieties for propagation by grafting 
 and budding has gone on for so short a period (15 to 20 years) that 
 improvements may be confidently expected in the future. 
 
 In considering the varieties to plant, one should select only those 
 which meet the requirements for a first-class commercial nut to be 
 sold in the so-called "budded" grade. 7 
 
 6 The average price for seedling walnuts sold by the California Walnut Growers ' 
 Association during the 12-year period, 1909 to 1920, inclusive, is, for No. 1 soft- 
 shell nuts, 18.2 cents per pound. During the same period, Fancy Budded nuts 
 averaged 21.3 cents per pound. 
 
 7 At present only a portion of the varieties of the California walnuts are sold 
 at wholesale under their varietal names. The Eureka, Franquette, Mayette, Payne, 
 and Concord are sold at such; the Placentia, which comprises a greater bulk than 
 all other grafted varieties combined, is sold under the general term "budded." 
 
 As the ' l budded ' ' nuts are graded in the packing houses of the California 
 Walnut Growers' Association, they pass through a large galvanized iron cylindrical 
 grader, 10 feet long and 40 inches in diameter. This grader, which revolves 
 slowly, at a 6-inch pitch, has a capacity for propely grading about one and a half 
 tons of nuts per hour by passing them over somewhat less than 8000 l% G -ineh 
 
Bulletin 332] WALNUT CULTURE IN CALIFORNIA 155 
 
 A heavy shell and a firmly sealed nut are essential to withstand 
 the handling in the grading, packing, and commercial operations 
 without cracking open. A nut which is partly cracked open soon 
 becomes rancid and must, therefore be eliminated from first-class 
 grades. The proportion of kernel to the total weight in a sample of 
 carefully graded nuts is slightly less than 50 per cent. 
 
 DESCRIPTION OF VARIETIES8 
 
 (Described in order of their popularity in 1920.) 
 
 PLACENTIA 
 
 The Placentia may at present be considered the best varietj^ of 
 walnut which has been proved thoroughly successful, commercially, 
 in southern California. At present most of the nuts sold in the 
 "budded" grade are of this variety. The defects of this variety will 
 be stated first, and its good qualities later. 
 
 Probably the greatest defect of Placentia is' its pronounced sus- 
 ceptibility to blight. During 1915 and 1916 many of the Placentia 
 groves blighted as badly as the average seedling groves, although from 
 1917 to 1920, when there was little blight, this variety was particularly 
 profitable. The second defect is the tendency of the nuts -to spring 
 open at the apex if they are dried too rapidly by exposure in the sun 
 during the curing process. 
 
 The variety is readily propagated by grafting upon the black 
 walnut, making a thrifty, rapidly growing tree. The Placentia usually 
 bears young in southern California, and produces very good crops. 
 It is regular in its bearing habits and lacks the tendency of some sorts 
 to bear every other year. The nut has the desirable size for com- 
 mercial sale, being oval, with a fairly smooth shell. The nuts tend 
 to vary in form, and some strains are more nearly round and some- 
 what roughened. The nuts are not well sealed. The shell is thin, 
 but strong. The kernel is smooth, plump, and light colored, and is 
 taken as a standard of quality and appearance for the budded grade 
 of nuts. 
 
 square opening's. The nuts which drop through the openings are known as the 
 Standard Budded grade; those which are too large to pass through the openings 
 come out at the lower end of the grader and are known as the Fancy Budded 
 grade. The latter grade, composed of the larger nuts, constitutes the highest 
 priced, so-called " budded" nuts. In addition to the size requirements here de- 
 scribed, an ideal budded nut should have a plump, sound kernel of a bright, light- 
 straw color, and be free from mould. The shell must be of a clear, bright color, 
 free from any discoloration. 
 
 * For a more complete description and history of the following varieties, as 
 well as the more uncommon ones, see Univ. of Calif. Experiment Station Bull. 
 No. 231, 1912, and U. S. Dept. of Agr., Bur. of Plant Indus., Bull. No. 254, 1913. 
 
156 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 The Placentia variety has been grown with marked success 
 throughout the coastal sections of southern California, and some of 
 the best grafted trees in the inland valleys of the south are of this 
 variety. The Placentia has not become popular with the walnut 
 growers of central or northern California, because it seems to lose 
 there some of its tendency for precocity and heavy production, and 
 is further hampered by its production of dark-meated nuts. 
 
 EUEEKA9 
 
 This variety was originally selected because of its supposed resist- 
 ance to walnut blight, the heavy production of the parent tree, and 
 the exceedingly high quality of the nut. The supposed resistance to 
 blight is largely mythical. 10 The mistake was due probably to the 
 great variation in blight occurrence during different seasons, with the 
 possibility that, during the early years of observation of this variety, 
 the blight may not, have been normal in its prevalence or season of 
 occurrence in the district surrounding the original tree. 
 
 The Eureka is not usually so readily propagated upon the black 
 walnut root as some of the Santa Barbara soft-shell varieties. The 
 trees are vigorous growers, although the growth may not be so great 
 as that of the Placentias in the same orchard. The Eureka is later 
 in reaching an age of profitable bearing than the Santa Barbara soft- 
 shell varieties in southern California, and although the high quality 
 of the Eureka nuts causes them to sell for more than the Placentia 
 the difference averages only about 2y 2 cents a pound. This higher 
 price has not made up for the lighter crops which are obtained, in 
 most instances, during the -first 10 to 15 years. Comparisons cannot 
 be made between mature trees of these varieties, as the Eureka has 
 been so recently introduced. In some instances the Eureka seemed 
 to have a tendency toward biennial bearing. It is to be hoped that 
 this variety may prove more productive in southern California as 
 the trees become 15 to 20 years old, as the nut itself has many points 
 to commend it, and large acreages have been planted with this variety. 
 
 The tree blooms much later than most other varieties and often 
 escapes injury to the flowers bj^. late spring frosts. Its harvest season 
 
 9 The parent tree of the original Eureka tree was a Persian or Kaghazi type 
 of walnut which grew on the old Meek estate near Hayward, California. The 
 seedling which developed into the original tree is now a mature tree near Fullerton, 
 California. 
 
 io For account of the blight occurrence in the Eureka walnut, see Fawcett and 
 Batchelor, ' f An Attempt to Control Walnut Blight, ' ' Monthly Bulletin, Dept. of 
 Agric, State of California, May-June, 1920, p. 177. 
 
Bulletin 332] 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 15' 
 
 is fully three weeks later than that of seedling nuts, or of the Placen- 
 tia. This is a distinct disadvantage in marketing the crop in the 
 eastern cities in time for the holiday trade. 
 
 Fig. 3. — Placentia. 
 
 The Eureka variety has suffered a great deal from injury caused 
 by being frosted during the early fall. Whether this is due to a 
 characteristic of late ripening, or to the possibility that the Eureka 
 has been planted in places more subject to frost than other varieties, 
 cannot be definitely stated at this time. 
 
158 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 The Eureka may escape with less injury from sunburn than do 
 some varieties, as its leaves are larger and the nuts are borne in a 
 position on the twigs which affords more natural protection than most 
 varieties have. This does not make the Eureka entirely immune from 
 sunburn injury, however, especially if the hot weather occurs in June 
 or early July, when the nuts are only half-grown, and before the 
 foliage is fully developed. 
 
 The Eureka nut is easily distinguished from any other variety 
 grown in southern California by its pronounced elongation, rather 
 straight parallel sides, slightly rounding to square ends, with the apex 
 usually broader and more nearly square than the base. The color of 
 its shell is a bright straw, of a lighter, more attractive shade than the 
 typical soft-shell nuts. The extra heavy shell and the exceptionally 
 and completely firm "seal" of the nut, make it a model nut for good 
 keeping qualities, and for withstanding commercial handling. A 
 well-grown Eureka nut is filled to its full capacity with a light, cream- 
 colored, plump,. waxy, kernel, with rather deep convolutions, possess- 
 ing the very best of eating qualities. The Eureka is richer and freer 
 from astringency than the soft-shell varieties. 
 
 This variety has made many friends in central California around 
 Stockton and San Jose, and in some of the hot inland valleys of 
 southern California, where it seems to be more promising for profitable 
 production than the Placentia. 
 
 The kernel of the Eureka walnut will not fill out perfectly on all 
 four quarters unless the trees are amply supplied with soil moisture. 
 The variety has been disappointing in some of the central California 
 districts, where the trees have not been adequately supplied with 
 irrigation water. 
 
 On the merits of its eating quality and the attractive appearance 
 of its kernel it might be expected to out-sell the Placentia more than 
 2y 2 cents a pound ; however, this average figure of the past is the only 
 safe guide in projecting a business undertaking. It is to be hoped 
 that this superior nut will eventually prove to have the tree and 
 bearing characteristics necessary to make it the leading variety in 
 southern, and more especially, central California ; the evidence at hand, 
 however, does not justify an unqualified business confidence that such 
 hopes will be realized. 
 
BULLETIN 332] WALNUT CULTURE IN CALIFORNIA 159 
 
 EHRHAEDT 
 
 This variety has only recently been planted commercially. 11 
 
 Origin. — The location of the original seedling tree from which this 
 variety sprang is apparently unknown. The tree was first selected 
 and propagated by the late D. C. Disher, who sold fifty grafted trees 
 to V. E. Ehrhardt, of Santa Ana, during the spring of 1906. The 
 variety had not been given a name by Mr. Disher at that time, but 
 the above trees were delivered as a substitute for Placentia, with 
 Mr. Ehrhardt 's sanction. Mr. Disher 's only explanation and descrip- 
 tion of the trees was that they were propagated from a selected Santa 
 Barbara soft-shell seedling tree of unusual superiority, and he further 
 announced his intention of propagating from this tree extensively 
 and offering it to the trade as a new variety. Unfortunately, Mr. 
 Disher died soon after the above transaction, without disclosing the 
 location of the original tree. 
 
 The writer's attention was first called to these grafted trees by 
 Mr. Charles Knowlton, of Fullerton, in the spring of 1915. Since 
 then, many observations have been made, especially to determine the 
 amount of blight prevalent and the yields of the several seasons. The 
 variety has attracted considerable attention locally, and is now com- 
 monly known as the "Ehrhardt." 
 
 Following is a description of the nut and the trees : 
 
 Nut 
 
 Size. — Larger than the average Santa Barbara soft-shell nut, 
 requiring approximately 34-40 nuts to weigh a pound. 
 
 Form. — Broadly oval, base rounding, sometimes slightly pointed, 
 apex rather blunt, suture shallow, flange rather prominent. 
 
 Surface. — Medium to smooth. 
 
 Color. — Medium light brown. 
 
 Cracking Quality. — Nuts well sealed at both ends" when properly 
 handled at harvest season ; kernels readily cracked out whole. 
 
 Kernel. — Very plump and well developed, usually of a light tan 
 color. Good market type, averaging about 50 per cent of the total 
 weight of the nuts. 
 
 Flavor. — Mild, pleasant, and free from any decided astringent 
 character. 
 
 ii For a detailed description and history of all other varieties mentioned here, 
 the reader has been referred to publications which were issued before the public 
 appearance of the Ehrhardt. A similar account of this walnut is therefore given 
 here. 
 
160 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 Tree 
 Foliation Period. — Quite early, about same as Placentia. 
 Growth. — Vigorous, typical of this type of nut-tree, producing a 
 large amount of lateral twigs. 
 Foliage. — Dense. 
 
 Harvest Season. — Medium to early. 
 
 Precocity. — Very early producer; apparently this is second to 
 none. There are 38 of the original planting on Mr. Ehrhardt's prop- 
 erty at the present time ; their average yields for six years are shown 
 in the table under productiveness. 
 
 Productiveness. — This is very heavy producing variety, as shown 
 by the following yields of the original 38 trees on Mr. Ehrhardt's 
 property. 
 
 10th season (1915) 80 lbs. per tree. 
 11th season (1916) 76 lbs. per tree. 
 12th season (1917) 79 lbs. per tree. 
 13th season (1918) 81 lbs. per tree. 
 14th season (1919) 117 lbs. per tree. 
 15th season (1920) 98 lbs. per tree. 
 
 The Ehrhardt walnut is of the Santa Barbara soft-shell type, 
 closely resembling in some ways the Placentia. It is somewhat 
 rougher, slightly larger and better "sealed." The kernel gives the 
 impression of being plumper than that of the Placentia, because its 
 convolutions are very shallow. 
 
 It is as yet too soon to make definite statements concerning the 
 commercial value of this variety. It will probably succeed where the 
 Santa Barbara soft-shell succeeds. After observing the thirty-eight 
 trees on Mr. Ehrhardt's place for six years, it seems reasonable, to 
 expect that the Ehrhardt will some day prove its superiority to the 
 Placentia as a heavy yielding variety. The Ehrhardt trees were nearly 
 free from blight during 1915 and 1916, when this disease was very 
 widespread. At no time did the writer observe as much as 5 per cent 
 of blighted nuts on the Ehrhardt trees, while Placentia trees in the 
 same orchard were blighted as badly as 45 per cent, and seedlings 
 showed 65 per cent by actual count. Since 1916, the outbreaks of 
 blight have not been severe enough to really test this character of 
 the Ehrhardt. 12 However, whether largely resistant to blight or not, 
 
 12 No explanation can be offered of the freedom from blight of the Ehrhardt 
 trees during 1915 and 1916. The Placentia trees were of the same age or younger, 
 growing in the same orchard, and across a narrow highway. The two varieties 
 bloom at practically the same time. 
 
Bulletin 332] 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 161 
 
 its tendency to produce very heavy crops of high-grade nuts, appar- 
 ently out-yielding the Placentia, makes this new variety worthy of 
 commercial trial. 
 
 Fig. 4. — Eureka. 
 
 The Ehrhardt is readily propagated upon the black walnut root, 
 making a tree of medium vigor which bears at an early age. The 
 nuts are considered very promising by the wholesale trade. They 
 easily qualify in the budded grade of walnuts. 
 
162 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 PAYNE 
 
 Although the parent tree of this variety was discovered by G. P. 
 Payne, near Campbell, California, in 1898, the variety has not been 
 widely planted and only in recent years has it been propagated in 
 any great quantity. The precocity of this variety for heavy pro- 
 duction is probably the chief characteristic which has brought it into 
 prominence during the past four years. It must be kept in mind, 
 however, that walnut blight has not been prevalent to a great degree 
 during 1918 to 1920. Moreover, the Payne is notoriously subject 
 to blight during seasons of bad outbreaks. The recent rise in popu- 
 larity of this variety may be very much altered if walnut blight 
 prevails in the future as it did during the seasons of 1915 and 1916. 
 
 The Payne tree makes a rather slow growth, possibly because of 
 its very heavy production as a young tree. The nuts are borne rather 
 prominently on the outside of the trees and are thus subject to severe 
 sunburning in the inland valleys. 
 
 The nut is oblong, rather pointed at the apex; shell of medium 
 thickness, somewhat pitted; well sealed; kernel full, with moderate 
 convolutions and of good quality. With the heavy production of the 
 oldest trees growing at present, there seems to be a reduction in the 
 size of the nut, making a high percentage of No. 2 grade. This nut 
 has not been sold in the Fancy Budded grade, but has been sold under 
 its varietal name. During the 1921 season it sold for less than the 
 California Walnut Growers' Association "Fancy Budded" grades, 
 but for one cent per pound more than the seedlings. 
 
 The greatest popularity of this variety is found perhaps in the 
 Stockton, San Jose, San Fernando, and Elsinore districts. In the first 
 mentioned district it is as popular as the Eureka. It might be suit- 
 able to interplant in a Eureka grove. Thus, the first ten years of the 
 slow-developing productivity of the Eureka would be bridged over 
 by this prolific and precocious variety. In the districts of the coastal 
 counties where the blight is most regularly severe and prevalent, the 
 Payne variety certainly cannot be recommended for permanent trees. 
 The greatest value of this variety may prove to be its precocity and 
 thus its value as a temporary interplanted tree among slower develop- 
 ing but superior varieties. 
 
 CONCOED 
 
 The Concord is one of the best tested varieties for the central 
 portions of California, especially in Contra Costa and Napa counties, 
 where many thousand trees are growing. In these districts, it has 
 
Bulletin 332] 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 163 
 
 proved to be a vigorous, thrifty tree, and an annual producer of 
 medium sized crops. The Concord blooms nearly as late as the 
 Eureka, but possibly the nuts mature a week earlier than the latter 
 
 Fig. 5.— Ehrhardt. 
 
 variety. The trees are fairly precocious. The nuts are elongated and 
 somewhat pointed at the apex ; the shell is rather smooth ; the nuts 
 are poorly sealed, the kernel fairly plump, with medium to deep 
 convolutions, only medium light-colored and of good quality. This 
 variety is not so well received by the wholesale trade as the Placentia 
 
164 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 
 
 or Eureka, It is doubtful if it should be planted where the two above- 
 mentioned varieties will succeed. In southern California the Concord 
 does not yield so well as the soft-shell varieties, so far as they have 
 been observed by the writer. Possibly the oldest Concord trees in 
 southern California are a group of top-grafted trees on the Pasadena 
 sewer farm. The trunks are soft-shell seedlings, while the tops, now 
 10 or 12 years old, are as large as 15 to 20 year old trees. This group 
 of Concords has produced, annually, a medium crop during the past 
 four years. Nothing definite can be said about the blight, as it has 
 not been severe anywhere in this orchard during the period under 
 consideration. 
 
 FEANQUETTE 
 
 This variety has been tested longer in central California than any 
 other. Successful commercial plantings of Franquettes occur in 
 Sonoma, Napa, Contra Costa, Santa Clara, and Tulare counties. This 
 variety has many adherents in these sections because of its regular 
 bearing of moderate size crops of excellent quality. The Franquette 
 has borne too lightly in the Stockton district to be recommended for 
 commercial use. In southern California, the Franquette has not 
 proved commercially successful, owing to its slow growth and light 
 crops. 
 
 The Franquette is late in reaching a bearing age. It blooms very 
 late, and the harvest season is too late for the most advantageous 
 disposal of the crop for the eastern holiday trade. Owing to its late 
 blooming it usually escapes injury by late spring frosts. 
 
 The nut is large, elongated, pointed, fairly smooth, and of a lighter, 
 clearer and more attractive color than the soft-shell types. The shell 
 is thin, but well sealed, and fairly well filled with a very light colored, 
 moderately plump kernel. The eating qualities of the Franquette are 
 unsurpassed by any variety grown in California. The high quality 
 of this nut makes it sell for a higher price than most other varieties 
 grown in the state, except the Eureka, 
 
 Where ample irrigation water is available, the Eureka seems to be 
 gaining in favor more rapidly than the Franquette. In sections of 
 rather heavy winter rainfall, where walnuts are usually grown by 
 dry-farm methods, it is probable that the Franquette will be chosen, 
 as the Eureka may not produce a well-filled, plump kernel under such 
 conditions. The heavy weight of the Eureka nuts may make them 
 preferable even in the localities where the Franquette is successfully 
 grown, if the soil moisture conditions are favorable to the former 
 variety. 
 
Bulletin 332] WALNUT CULTURE IN CALIFORNIA 165 
 
 ROOTSTOCKS 13 AND CHOICE NURSERY TREES 
 
 CHOICE OF EOOTSTOCK 
 
 The choice of rootstocks for the walnut has narrowed down during 
 the past 20 years to a predominating' preference for the northern Cali- 
 fornia black walnut (J. hindsii). The seed is shipped commercially 
 by several agencies from central California for this purpose. Groups 
 of dooryard and border trees usually furnish this seed. Some 
 nursery men in southern California have located and use seed from 
 particularly vigorous black walnuts of this species, which have been 
 planted locally. The seedlings from a group of such trees vary con- 
 siderably, and in some instances certain trees are especially valued 
 because of their tendency to produce uniform and vigorous seed- 
 lings. This species of black walnut will apparently withstand a more 
 unfavorable soil condition than the seedling English walnut. Its 
 resistance to oak-root fungus (ArmMaria mellea) is also a valuable 
 characteristic of this rootstock. The northern California black walnut 
 is more vigorous as a nursery tree than the eastern black walnut, 
 which was formerly used to some extent, only to be discarded in recent 
 years. 
 
 The southern California black walnut (J. Galifornica) is seldom 
 used at present, because of its tendency to sucker profusely at the 
 crown as an orchard tree, and its susceptibility to root-rot troubles 
 on heavy or poorly drained soils. 
 
 The paradox-hybrid walnut, which is a cross between the English 
 and any of the black walnuts, makes a remarkably rapid growing tree. 
 Mature trees may have a spread of over sixty feet. The vigor of this 
 first generation hybrid has been mainly responsible for its popularity 
 among some planters. Such trees cannot be secured in quantity, how- 
 ever, so that their use will always be restricted. The increased vigor 
 of the first-generation hybrid is not carried on to following genera- 
 tions; in fact, the first-generation hybrid trees are usually nearly 
 barren and their seedlings show many types of growth and vigor, 
 making undesirable rootstocks. 
 
 The Koyal-hybrid walnut is a cross between the eastern black 
 walnut and the California black walnut. It is thought by some, that 
 the second-generation Royal-hybrid is equal or even superior to the 
 northern black walnut as a rootstock. There may be such hybrid 
 strains which justify this confidence, but, as a whole, it cannot be said 
 that such superiority has been proved. Seedlings from some of the 
 Royal-hybrid trees produce uniformly vigorous trees, while those from 
 
 13 For details of nursery propagation, see Univ. of Calif. Experiment Station 
 Bull. No. 231, 1912. 
 
166 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 others are variable to a great degree and lack vigor. Very likely the 
 pollinating parent has much to do with this lack of consistency. 
 
 METHOD OF PEOPAGATION 
 The English walnut is usually grafted on to the black walnut root 
 during the early spring, using a whip graft. It can be budded, 14 
 however, and some nurserymen prefer this method. 
 
 EEQUIEEMENTS FOE GOOD NUESEEY TEEES 
 In the case of the grafted trees, the black walnut trees are grown 
 one year in the nursery and then grafted in late winter ; the grafted 
 trees should grow from 6 to 12 feet the summer following. Such trees 
 are trained to a whip growth and usually sell according to size, a 
 premium being placed upon the larger trees. The pre-war price of 
 well-grown walnut trees was from $1.00 to $1.50 ; during 1919-21 
 trees have sold as high as $3.00 each for 6 to 8-foot trees. A medium 
 sized tree (8 to 10 feet) may be preferable to either an extremely large, 
 or a small tree. A very large tree may be injured considerably in 
 digging from the nursery, while a small tree may be a stunted tree 
 with a poor root system and never make a first-class orchard tree. 
 
 STARTING THE YOUNG ORCHARD 
 
 LAYING OUT THE OECHAED 
 
 From 12 to 27 walnut trees per acre are found in the mature 
 orchards. General observation and the opinions of many walnut 
 growers seem to agree that the plantings of the past have been made 
 with the trees too close together in many instances. 
 
 If the trees are spaced 60 feet apart each way, planted on the 
 square system, it will require 12 trees per acre ; orchards planted in 
 this manner are among the most productive in the state. When 
 spaced 60 feet apart, the individual trees have ample room to develop 
 fully and a large proportion of the nuts are produced on the side 
 branches. With only 12 trees to the acre the root systems of the 
 trees are not so crowded as in closer planting, and the trees maintain 
 a healthy vigorous growth of new fruiting wood when they are thirty 
 years old, or older. 
 
 i* The question is often asked: "What is a budded walnut?" The grade of 
 nuts sold under the name ' * budded ' ' has no doubt prompted this question in many 
 instances. A budded nut is any one of the varieties which will grade according 
 to the standard of perfection set by the Placentia. The tree which bears such 
 a nut has been produced by budding or grafting a bud or scion of the variety in 
 question on a black walnut rootstock. The English, or the hard-shell, are seldom 
 used as a rootstock at present. If budded, the work is usually done in August, 
 using a patch or a shield bud from the current season's growth. 
 
Bulletin 332] WALNUT CULTURE IN CALIFORNIA 167 
 
 Jn the close plantings, where the trees are only 40 to 50 feet apart, 
 the side branches are shaded most of the day, the fruit spurs on the 
 lower branches soon die, and the crop is borne mainly in the tops of 
 the trees. A closely planted grove is illustrated by Fig. 6. Such 
 orchards have not maintained their productivity so well as those 
 planted further apart. Plantings where the trees are now growing 
 40 or 45 feet apart can be thinned out by removing every other tree 
 in each row so that the trees alternate, or stand opposite a space in 
 the adjacent rows, then the remaining trees will stand approximately 
 57 or 63 feet apart respectively, in the rows, running diagonally across 
 the orchard. This may be made clearer by the following diagram : 
 
 DIAGEAM I 
 
 Showing Method of Thinning Out Too Closely Planted Orchards 
 
 O Permanent trees to remain. 
 X Trees to be pulled out. 
 
 Figure 7 shows a view in an old seedling orchard after the thin- 
 ning process had advanced to the stage of cutting off the tops of the 
 condemned trees, ready for the stump puller. This paragraph con- 
 cerning thinning old orchards is placed here under the general heading 
 of planting with the realization that many prospective walnut planters 
 can benefit by the experience of those who have blazed the way in 
 this industry. 
 
 One of the most favored systems of planting at present is to plant 
 the trees in rows 60 feet apart with a distance of 30 feet between the 
 trees in the rows. The trees may be all of one variety, or, in localities 
 where the varietal adaptation is in question, two varieties may be 
 planted alternately. When planted according to this latter method, 
 there is less hazard of planting the wrong sort, as one may have a 
 choice between two varieties after they reach a bearing age. Such 
 
168 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 plantings are usually thinned out when the trees are from 10 to 14 
 years old, according to the variety, soil, water and climatic conditions. 
 They should not be left until they crowd badly. By this method, 
 properly carried out, nearly twice the tonnage per acre may be ex- 
 pected during the first 10 or 14 y ears' growth as where only the 
 permanent trees are planted. At the same time, there is practically 
 as much room for intercrops, such as beans, during the early life of 
 the orchard as where only 12 trees are planted per acre. The extra 
 expense of buying and planting filler trees may be paid for by part 
 of a year's crop, while all other extra expense due to the filler trees, 
 such as pruning, extra water, etc., is of minor importance. 
 
 The following diagram illustrates this plan of setting out filler 
 trees. 
 
 OXOXOXOXO 
 
 oxoxoxoxo 
 
 o.- Permanent trees 
 x.- Filler trees 
 
 -- ::: space for intercrops 
 
 CAEE OF TEEES BEFOEE PLANTING 
 If the trees are received from- the nursery before the ground is 
 ready for planting, they should be unpacked and heeled in, in a shady 
 place. Water the soil around the roots thoroughly after heeling them 
 in. If it is more practical, the trees may be held for a time under a 
 shed with the roots packed in damp sawdust or shavings. 
 
 Just before planting, the root system should be trimmed, to cut 
 off any mutilated portions of the tap root or lateral roots. In fact, if 
 the ends are all cut back slightly with a sharp pruning knife, leaving 
 a clean smooth cut, the new rootlets will start out much more readily 
 from such a surface than from a ragged cut or a torn and bruised root. 
 
Bulletin 332] 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 169 
 
 
 ^^^M^^^m^^^^^^ 
 
 Fig. 6. — The trees iu this orchard were planted too close, being spaced 40 feet. 
 They are producing walnuts only in the tops and will soon have to be thinned in 
 order to obtain a satisfactory yield per acre. 
 
 Fig. 7. — A grove showing every other tree removed in each row, so that the 
 trees alternate. 
 
170 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 PLANTING THE YOUNG OECHAED 
 
 Walnut trees should be planted during January and February 
 so that the soil may thoroughly settle around the roots, and growth 
 start with the beginning of the normal growing season, which is usually 
 early March, in southern California. Holes should be dug deep 
 enough to allow room for the full length of the tap root, which may 
 be from 18 to 30 inches. The lateral roots may be 6 or 8 inches long, 
 and the hole should be wide enough to accommodate them without 
 cutting back except to remove mutilated portions. 
 
 In filling in the soil around the roots, it is advisable to use the top 
 soil, tamping it thoroughly without bruising the roots. A better stand 
 of trees may be expected, and a more prompt growth in the spring, 
 if the young trees are thoroughly irrigated as soon as they are planted. 
 This can be accomplished by running a single furrow along the row 
 and cutting the water in at each basin left around the trees as the 
 holes are filled. Irrigation at this time may not be essential from the 
 point of view of soil moisture available, but it will be worth the pains 
 as a means of thoroughly settling the soil around the roots to prevent 
 them drying out. A few light rains should not mislead the planter 
 and cause him to omit this first irrigation at planting. 
 
 TEAINING YOUNG TEEES 
 
 If walnut trees are allowed to grow without any pruning, they will 
 usually take their natural form of a medium tall, upright, pyramidal 
 tree, with a pronounced central leader. At the time of planting, 
 walnut trees are usually headed back 5 or 6 feet from the ground, and 
 the upper lateral bud will frequently make an upright limb which 
 will take the place of the removed top and continue the leader form 
 of tree. If this central branch is pruned off, however, the lower 
 lateral branches will form a more open vase-shaped tree. These lower 
 lateral branches thus once started, take all the strength of the tree 
 and another leader seldom becomes established. Figure 8 shows an 
 eight-year-old tree growing as a leader type. 
 
 Both the central leader and the open vase types of trees have their 
 k advocates. The advantage of the leader type of tree is primarily in 
 the greater strength of the framework, there being many more lateral 
 limbs distributed along a greater space on the main trunk than with 
 the vase-shaped type, and thus less likelihood of breaking, compared 
 with the latter type. In the case of the vase-shaped type the few 
 branches originate at nearly the same point on the main trunk and 
 
Bulletin 332] 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 171 
 
 this centralizes the strain of supporting the crop. In the case of 
 the vase-shaped trees, it is not unusual for one-quarter or one-half 
 of the tree to break off and, in extreme cases, there may be a split down 
 the middle and the tree be entirely destroyed. 
 
 Fig. 8. — Central leader type of walnut tree, 
 of branches, and plenty of fruiting wood. 
 
 This type has a strong framework 
 
 Figures 9 and 10 show walnut trees eleven years old, which were 
 trained to the open vase shape. It was necessary to have from 15 to 
 20 per cent of the trees in this grove braced by the time they reached 
 an age of profitable bearing. Eventually the owner will have to go 
 to the expense of bracing nearly every tree in the grove. The examples 
 here illustrated may be considered extreme because the lateral limbs 
 originate at so nearly the same point. 
 
172 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 The advocates of the open vase-shape tree claim that a greater area 
 of fruiting' wood is exposed to the sun in this form of tree than in 
 the leader type. This point is hard to verify, and the greater hazards 
 of breaking may offset any such supposed advantage. 
 
 After one has decided upon the type or ideal toward which the 
 young trees are to be trained, the pruning operations should be con- 
 sistent in following this initial decision. In training the young walnut 
 tree, very little pruning is necessary. .Walnut trees as they are 
 received from the nursery are usually one-year-old whips. If vigorous 
 8 to 12-foot trees are planted they are usually cut back to within 5 
 or 6 feet of the ground. 
 
 Trees thus planted will frequently start to grow first from the 
 lower buds within 12 to 24 inches of the ground, or will send out shoots 
 along their entire length. This growth should be rubbed off by going- 
 over the trees frequently during the early summer, keeping all buds 
 off which occur within 4 or 5 feet from the ground, according to the 
 form of tree to be grown, and their height at planting. If the lower 
 lateral buds have made a growth of 8 to 10 inches it is advisable to 
 "pinch off" the growing tips which will have the effect of forcing the 
 growth of the upper shoots, while the growth of the lower shoots is 
 restricted. The smaller lower shoots thus produce shade and nourish- 
 ment for the trunk. If the lower dormant buds are rubbed off at 
 planting, all the growth will take place in the upper buds without 
 further attention. If, on the contrary, these lower buds are allowed 
 to grow, the buds on the upper 24 inches of the tree may remain dor- 
 mant; in fact, in many instances the upper portion of the tree dies 
 back 12 to 24 inches. With the lower buds suppressed, however, the 
 upper buds are forced into growth and the framework of the tree is 
 started in the upper 24 inches of the trunk. 15 This is illustrated by 
 Fig. 11. 
 
 is A few planters advocate cutting the young tree back to within 12 to 16 inches 
 of the ground. This method forces into growth the latent buds near the ground; 
 one of these is selected to make the tree, and all others are rubbed off. The 
 selected shoot must be staked and tied to a 2" X 2" stake, 5 to 6 feet tall, other- 
 wise the supple growth will be whipped around and bent over by the winds. It 
 is claimed that this method gives a better stand of trees, and less liability of sun- 
 burn injury on the trunk. The tops thus cut back are relatively surer to balance 
 up with the root systems injured by digging. It may well be doubted if the extra 
 expense in staking and in the care necessary to grow a tree in this manner will 
 repay for the assurance of the growth of a larger percentage of the transplanted 
 trees. Good, plump nursery trees, if handled properly, should transplant very 
 readily and make nearly a 100 per cent stand of trees without resorting to this 
 severe cutting. If they are thoroughly whitewashed, or use is made of tree pro- 
 tectors, sunburning need not be feared. It may be advisable, however, if one 
 is using inferior trees or such as have dried out in transit, to cut them back within 
 16 inches of the ground. 
 
Bulletin 332J 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 173 
 
 Whether the ideal selected is the leader type or the open vase 
 shape, it is desirable to select the lateral branches for the framework 
 of the tree, spaced as far apart as practical when the young trees are 
 pruned at the end of the first year's growth. 
 
 
 
 3ai££> ; '*"'"4V« • w : * : '*k 
 
 F5#i-.d®" 
 
 Fig. 9.— Result of heading low, starting all the branches from one point. This 
 could have been prevented when the tree was young by spacing the branches 
 through a greater distance on the trunk of the tree. 
 
 With the vase type this perpendicular spacing throughout 18 to 24 
 inches will give greater strength to the framework than grouping the 
 
174 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 branches at more nearly one point of origin. The lateral branches 
 to be left for the framework of the tree may be 3 to 5 in number, as 
 evenly spaced as possible as they radiate outward from the trunk. 
 
 Fig. 10. — Method of bracing open vase type of tree to prevent splitting. 
 
 The upper or second bud from the top of the original tree will usually 
 produce a branch which grows in a nearly upright position ; this, of 
 course, should be "pinched back" during the early summer or cut 
 
BULLETIN 332] WALNUT CULTURE IN CALIFORNIA 175 
 
 out during the dormant season, in forming the framework of an open 
 vase-shaped tree. Figure 12 illustrates an example of this type of 
 tree. 
 
 In the case of the leader type it is essential to space the laterals 
 far apart and not leave too many; otherwise the leader, or central 
 shaft, will be "choked" out, as illustrated by Fig. 13. Only two or 
 three of the laterals should be left in addition to the central leader 
 at the end of the first year, as other lateral branches will grow out 
 during the following years from the central leader; thus the shape 
 of the trees is formed during the first two or three years' growth. 
 The branches which are left on the tree are not cut back in common 
 practice and by all means the leader should not be cut back. Figure 8 
 shows a desirable shape for a tree of this type. 
 
 Some of the most desirable types of trees judging from the view- 
 point of strength of framework and area of bearing surface, are a sort 
 of modification of both the leader and the vase-shaped type. Figure 
 14 illustrates such a tree; there is a pronounced leader through 4 or 
 5 feet of the main frame of the tree which finally divides up into a 
 strong, compact, spreading type of tree. This type can be trained 
 by maintaining the leader type through the first four years and then 
 during the dormant season, pruning back the leader to a strong lateral 
 branch 9 or 10 feet from the ground. The tree shown in the illus- 
 tration might well serve as a model, or ideal, in training young walnut 
 trees. 
 
 VALUE OF ORCHARDS AND LANDS 
 
 The valuation of walnut orchards and lands suitable for walnut 
 production varies considerably in the different localities and even in 
 the same districts. Such factors as suitability of the soil, water rights, 
 frost conditions, and proximity to transportation and civic centers 
 are reflected in the appraised valuation of walnut properties. The 
 value of established groves may be greatly influenced by the variety 
 of nut, rootstock, planting arrangement, etc. The average or the 
 most general valuations are all that can be presented here. 
 
 Replies to questionnaires sent out by the California Walnut 
 Growers' Association in 1919 and again in 1921, indicated that mature 
 bearing orchards are valued at about $1400 per acre, while the young 
 non-bearing properties are valued at approximately $900 per acre. 
 The following table shows the exact average valuation and the number 
 of properties considered. 
 
176 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 
 TABLE IV 
 
 
 
 Average Valuation of Walnut Groves 
 
 
 
 (Including water rights) 
 
 
 Year 
 
 observations 
 
 were made 
 
 Valuation 
 
 A 
 
 Number of 
 properties 
 represented 
 
 Bearing Non-bearing 
 
 1919* 
 
 $1299.02 $995.00 
 
 922 
 
 1921f 
 
 $1477.05 $828.65 
 
 231 
 
 Land suitable to walnut culture, plus adequate water rights, may 
 be purchased at from $600 to $1000 per acre in the proved walnut- 
 growing sections of southern California. Such land may have a rather 
 fixed value for the production of beans, beets, or even citrus fruits; 
 thus its potential value for walnut production is only one factor which 
 determines its appraisement. 
 
 In the central or northern portion of the State, where the walnut 
 industry is not so extensively developed as in the south, land which is 
 likely to prove suitable for walnut culture may be purchased for $200 
 to $300 per acre. This may not include a water right in any estab- 
 lished irrigation system, but such lands occur in areas where good 
 wells are known to exist. 
 
 CULTURE 
 
 SOIL MANAGEMENT 
 There is no one best way to cultivate all walnut groves. The 
 methods of performing the various operations of stirring the soil, 
 such as plowing, discing, and harrowing, vary widely in different 
 walnut groves. These different methods may give equally good results 
 in their respective groves, when measured by profitable crop produc- 
 tion. A practice which leaves one soil in first-class condition may be 
 very poor practice on another soil of a different type. Most walnut 
 trees are deep-rooted and it seems quite apparent in many cases that 
 the character of surface soil cultivation is of only minor importance 
 to the welfare of the tree, except as this cultivation affects the con- 
 servation and use of soil moisture by the tree. There are many door- 
 yard and roadside trees which produce heavy crops and yet the soil 
 around them may not be stirred from one year's end to another. It 
 does not follow from this, however, that a walnut grove should not 
 
 * ' ' The California Walnut, ' » p. 15, 1919. Published by The California Walnut 
 Growers' Association. 
 
 f Brief of Facts Eclating to the American Walnut Industry, p. 23, 1921. Pub- 
 lished by the Walnut Protective League. 
 
Bulletin 332 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 177 
 
 be plowed or cultivated. There are frequently many conditions sur- 
 rounding roadside and dooryard trees which are favorable to the pres- 
 ence of an abundance of soil moisture, which cannot be duplicated 
 under orchard conditions. Isolated trees have the advantages of 
 better exposure to sunlight and a far greater range for root develop- 
 ment and available soil moisture than trees planted in orchard form. 
 
 Fig. 11. — Walnut trees when planted are usually cut back to within 5 or 6 feet 
 of the ground. 
 
 (a) If they are not trained they will frequently send out shoots along their 
 entire length during the early summer. 
 
 (&) Frequently if the lower buds within two feet of the ground are allowed to 
 grow, the upper 24 inches of the trees may remain dormant. 
 
 (c) If the lower buds are suppressed the upper ones are forced into growth 
 and the framework of the tree is started in the upper 24 inches of the trunk. 
 
178 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 The majority of walnut groves are plowed once a year, usually in 
 the very early spring. A disc, springtooth or spiketooth harrow is 
 then used to put the land into good physical condition. The clean 
 cultivation during the summer months is done in relation to the irri- 
 gation practice and the conservation of soil moisture. 
 
 The practice of plowing the groves once a year seems essential 
 to most of the soil types found in the walnut districts of California. 
 The relation of such plowing to the penetration of the rains into the 
 subsoils and the application of irrigation water alone justifies the oper- 
 ation. Putting 6 to 10 inches of the surface soil into a friable, mellow 
 condition every year makes it practical to use deep irrigation furrows 
 and thus to insure deep penetration and a more complete use of the 
 irrigation water applied the following season. An annual plowing 
 prevents the tree roots from becoming permanently established in 
 the surface six inches of soil, and thus becoming subject to the great 
 variations of soil moisture content which occur there during the 
 summer months. 
 
 If the land is plowed in the fall and left rough, the rains may be 
 expected to penetrate deeper into the subsoil because of the lessened 
 run-off. This object is accomplished best, in some instances, if the 
 plowing is done at right angles to the grade of the land. Where a 
 winter cover crop is grown, fall plowing may be impractical because 
 of the necessity of planting the cover crop early, either just before 
 the harvest, or immediately after. When winter cover crops are not 
 grown, the practice of fall plowing has much to commend it. A 
 medium to light irrigation may well precede the fall plowing, and 
 the land left rough without further cultivation until the early spring. 
 Late spring plowing is objected to by some walnut growers as they 
 believe the cutting of the feeder roots by such plowing to be especially 
 harmful when the tops are just starting to grow, during late March 
 and the month of April. The instances which are frequently cited 
 to illustrate the poor crop conditions following late spring plowing, 
 are not readily diagnosed. It usually seems that there may be other 
 more important factors conducive to poor crops, accompanying the 
 late plowing. The dry soil condition which is so frequently correlated 
 with late plowing, may in itself be more truly responsible for the poor 
 crops than the mere season of plowing. Many orchards which are 
 plowed late are cover-cropped or heavily covered with volunteer 
 growth of barley, oats, native annual plants, etc. In most seasons, 
 and in most walnut districts, the presence in late March or early 
 April of a sown cover crop or a volunteer crop, may be taken as a 
 safe indication that the soil moisture is largely depleted, unless the 
 
Bulletin 332] 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 179 
 
 land has been thoroughly irrigated once or twice during the growth 
 of the crop. The orchard in which a volunteer crop is allowed to 
 grow is most likely to be neglected in regard to winter irrigation. 
 Many such orchards are plowed in the spring when the annual plants 
 have actually wilted for lack of moisture, or after recent rains have 
 revived them by moistening the soil only to the depth of the plow 
 
 Fig. 12. — A typical open-vase type of tree. 
 
 furrow. The subsoil from the second to the eighth foot, in groves thus 
 managed, may be nearly dust dry at this season when the trees are 
 commencing to leaf out. 
 
 The amount of water required to produce a cover crop is often 
 underestimated by the walnut grower. This is especially true when 
 the crop is produced during the rainy season and makes a satisfactory 
 growth without irrigation. This matter is more fully treated under 
 the heading "Cover Crops/' Many such instances of the above have 
 
180 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 been noted, when an examination of the subsoils has shown a dryness 16 
 hardly credible. The fact that the orchard was being plowed at the 
 time the observation was made, and a few feeder roots were being cut 
 in the late spring, has seemed to some observers as unimportant, com- 
 pared with the extremely unfavorable soil moisture conditions existing 
 at the commencement of the growing season for the trees. It seems 
 reasonably safe to assert that the chief factor contributing to poor 
 crops in many late plowed orchards is the dry soil condition during 
 the winter and early spring, and the late plowing which may be asso- 
 ciated with this dryness is in no great degree responsible. Late plow- 
 ing may be accompanied by ideal soil moisture conditions as noted 
 later, in which case the crops may not suffer. 
 
 Judging the question of late spring plowing from another angle, 
 there are many first-class, heavy producing orchards which are 
 annually spring-plowed in April, when the leaves are coming out on 
 the trees. Some of these orchards are located on the lowlands subject 
 to winter floods, where it is necessary to cover crop the land to prevent 
 erosion and where this threat of flood damage is not past until April. 
 Orchards in these districts are seldom or never plowed until late, yet 
 many of them produce approximately 2000 pounds per acre. Such 
 plantings are usually well irrigated during the spring or late winter 
 months, however, either by regular irrigation methods or by the 
 passage of flood waters over the lands. 
 
 This discussion should not be taken as an encouragement to late 
 spring plowing, as there are points in favor of plowing early and it 
 seems to be the practice most usually recommended by successful 
 walnut growers. This discussion is offered mainly to encourage 
 growers to feel that they may maintain a first-class walnut grove, even 
 though for any reason they are obliged to plow late, providing other 
 factors, chiefly soil moisture conditions, are favorable to the early 
 spring growth of the tree and nuts during March and April when 
 such plowing is frequently done. 
 
 • COVER CROPPING 
 The practice of cover cropping walnut groves prevails in probably 
 somewhat less than 50 per cent of the total area of bearing groves. 
 
 is Walnut groves have been examined by the writer in which the soil below 
 the penetration of winter rains contained only hygroscopic moisture. Walnut 
 trees commonly reduce the soil moisture to this point during the fall months. 
 A winter rainfall of 8 to 12 inches may not percolate below the second or third 
 foot of soil if there is a cover crop or weed crop growing on the land. If the 
 rains come in small amounts distributed over 5 or 6 months, as frequently occurs, 
 their shallow percolation is more pronounced than when large volumes fall at a 
 time. 
 
BULLETIN 332] WALNUT CULTURE IN CALIFORNIA 181 
 
 Many groves which are not sown to cover crops produce a volunteer 
 growth of various annual plants, such as bur clover, lupins, wild oats, 
 and alfilaria, during the rainy season. 
 
 There is very little or no definite information concerning the 
 subject of the effect of cover crops on walnut trees. 17 
 
 Though we have no definite field trials to inform us concerning 
 the effects of cover crops in walnut groves, a discussion of some of 
 the factors to be considered may be useful. Possibly the primary 
 factor is the problem of supplying sufficient irrigation water for the 
 walnut trees and the cover crop combined. While it is true that 
 walnut trees do not draw very heavily upon the soil moisture during 
 the winter months, yet it is highly important to have the water content 
 of the soil somewhere near optimum during the entire winter. It is 
 a mistake to allow a winter cover crop to deplete the soil of its neces- 
 sary moisture. There should be no misconception about the saving of 
 soil moisture because of the shade of the cover crop. This shade and 
 thus possible conservation of moisture in the few surface inches of 
 soil, is hardly worthy of mention, compared with the soil moisture 
 necessary to produce the cover crop itself. 
 
 The actual water required to produce a fair crop of the several 
 plants commonly used as cover crops in California, has never been 
 carefully studied, so far as known to the writer. A good general idea, 
 however, of the water requirements of such crops can be obtained from 
 both the controlled experiments with related plants, and the experi- 
 ences of farmers. 
 
 In studying the water requirements of certain plants, Briggs and 
 Shantz 18 found that different plants require different amounts of 
 water to produce equal quantities of dry matter. 19 
 
 The average requirement of alfalfa, field peas, and melilotus alba 
 was 803 pounds, which is more than is needed by common graius. 
 
 i? The beneficial effects of plowing under green manure crops, as measured by 
 the crops of annual plants which are later grown on the same ground, cannot be 
 used as a safe guide in theorizing on the effects of this practice on walnut trees. 
 In the case of annuals, there is no competition between the cover crop and the 
 primary crop. Even with annuals, much of the benefits ascribed to the cover crop 
 may have been due to crop rotation, as has been shown by various experiments 
 which were so laid out as to measure this latter factor. Again, the root zone of 
 many of the annual crops which have been used to indicate the effect of cover 
 crops upon the productivity of the soil, corresponds more closely to the root zone 
 of the cover crops than to that of the very deep-rooted walnut trees. 
 
 is The Water Eequirement of Plants, U. S. Dept. of Agric, Bur. of Plant 
 Indus., Bull. No. 284, 1913, p. 47. 
 
 19 Dry matter is that portion of the plant which remains after all the water 
 has been evaporated off by a temperature slightly above the boiling point of water. 
 
182 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 TABLE V 
 
 Water Requirements, Measurements of Crops at Akron, Colorado 
 
 Crop 
 
 Variety- 
 
 Water 
 
 requirement 
 
 (lbs.) 
 
 Alfalfa 
 
 Grimm 
 
 1068 
 
 Field peas 
 
 Canada 
 
 800 
 
 Sweet clover 
 
 (M. alba) 
 
 709 
 
 Average of three legumes 803 
 
 In the absence of any more information, we can use these results 
 to estimate the approximate water requirements of the cover crops 
 used in walnut groves. 
 
 Using this water requirement of 803 pounds of water as a guide, 
 and a yield of 13 tons per acre as an average yield, 20 with 20 per cent 
 dry matter, the example works out as follows : 
 
 5200 (lbs. of dry matter) X 803 (lbs. of water required per 
 lb. of dry matter) =4,175,600 (lbs. of water per acre) = 
 18.47 acre inches per acre of cover crop. 
 
 This figure of 18.47 inches is based upon control experiments where 
 the crops were grown in cans and the surface evaporation from the 
 soil was practically eliminated, whereas under orchard conditions 
 there is considerable loss from surface evaporation while the young 
 cover crop is becoming established during the early fall months. This 
 figure is, therefore, probably too low for orchard conditions. 
 
 Turning now to a practical example : A cover crop of yellow sweet 
 clover (M. indim) was grown in a one-year-old walnut grove on the 
 Citrus Experiment Station grounds during the winter of 1920-21. 
 The land was cropped to barley during the spring of 1920, and there- 
 fore contained practically no soil moisture available for the growth 
 of a cover crop in the fall of the same year. The cover crop was 
 planted in September, 1920, and plowed under in April, 1921, when 
 it was just past full bloom. The clover growth contained some volun- 
 teer barley, so that it closely corresponded to the cover crops in the 
 flood districts, where barley and clover are sown together. From the 
 date of planting until the middle of March, 15.8 acre inches of irriga- 
 tion water per acre had been applied to this crop. At this time the 
 clover was just starting into bloom and the land was so dry that it 
 could not be plowed with a mould-board plow until after it was irri- 
 gated. It was then irrigated with 7 acre inches per acre. By April 11 
 
 20 W. M. Mertz, Green Manure Crops in Southern California, Univ. of Calif., 
 Agric. Exp. Sta., Bull. No. 292, 1918, p. 10. 
 
Bulletin 332] 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 183 
 
 the land was again too dry to plow, and in addition to the irrigation 
 water previously given, 7.2 inches of rain had fallen during the growth 
 of the cover crop, making a total of 30.0 acre inches per acre which had 
 been used by the small walnut trees and by this mixed cover crop of 
 sweet clover and barley of maximum tonnage growing to maturity. 21 
 
 Fig. 13. — The central leader in this tree has been starved out by the lateral 
 branches, all starting out at nearly the same place and cutting off the food supply 
 from the central trunk. 
 
 2i At this time the land received an additional 7 acre inches per acre and was 
 then plowed as soon as practicable ; the last 7 inches should not be charged to the 
 cover crop, as it was largely conserved in the soil by prompt plowing, leaving the 
 soil in a good condition for the young trees and the planting of a summer intercrop 
 of beans. 
 
184 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 If the crop had been plowed just as the clover came into bloom 
 following promptly the March irrigation 22 there would have been 15.8 
 acre inches per acre irrigation water and 7.2 inches of rain, making 
 23 inches as a total used by the crop up to this period in its growth, 
 and leaving the soil quite as dry as it was the fall before. 23 The 
 stage of development of the crop at this time, just beginning to bloom, 
 would have been the ideal condition for plowing under. The tonnage 
 was nearly at its maximum, and the green succulent condition of the 
 stalks of both the clover and the barley would have probably assured 
 a more rapid disintegration after plowing than turning it under in 
 April, when the flowering season was practically past. 
 
 From the two examples cited, it seems probable that the growth 
 of a legume cover crop in a walnut grove should be expected to require 
 from 20 to 24 acre inches per acre of irrigation water, aside from the 
 needs of the trees. The winter rains alone are frequently no more 
 than sufficient to meet the requirements of the trees under clean 
 cultural conditions. In practice this will mean from 3 to 4 heavy 
 irrigations during the winter and early spring, in localities receiving 
 only 10 to 15 inches of winter rainfall. (See "Irrigation.") It is 
 sufficient here to remind the reader again that there should be ample 
 water available to grow the winter cover crop, and that following the 
 plowing in of the crop, the walnut trees should be given a thorough 
 irrigation at the commencement of their early spring growth. If 
 the requirements of the cover crop alone are considered, at the time 
 of plowing the subsoil may be entirely too dry to promote an early 
 vigorous growth of the trees and nuts, even though the soil is moist 
 enough to plow with a mould-board plow. 
 
 One of the benefits derived from the use of cover crops in walnut 
 groves has been the improvement of the physical condition of the 
 heavy soils as a result of the incorporation of large amounts of organic 
 matter. The experiences of many observing farmers seem to agree 
 that the clay loams are made more friable and the irrigation water 
 penetrates them much more readily when cover cropping is practiced. 
 The latter point, with reference to the deeper penetration of the irri- 
 gation water, may alone justify the use of cover crops on certain soils. 
 
 The legume cover crops most commonly grown in walnut groves 
 during the winter months are bur clover, yellow sweet clover (Melilotus 
 indioa), purple vetch, and horse beans. 
 
 22 It was too dry to plow before this irrigation, as noted. 
 
 2 3 The crop wilted badly before the March irrigation and the soil was judged 
 to be between the wilting point and the hygroscopic point. 
 
Bulletin 332] 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 185 
 
 The seed may be drilled in, or sown broadcast, and then " brushed 
 in" or harrowed lightly with a spike-tooth harrow. The amount of 
 seed required per acre is as follows : 
 
 Melilotus indica and bur clover 20- 30 lbs. per acre 
 
 Vetch 70- 80 lbs. per acre 
 
 Horse beans 100-200 lbs. per acre 
 
 Fig. 14. — One of the most desirable types of walnut tree, combining the good 
 points of both the leader and vase shape types. 
 
 It is essential to plant the cover crop as early in the fall as possible 
 after harvesting the nuts, in order that it may make a good start before 
 the cold weather commences, and thus make sufficient tonnage by the 
 middle of March to be worth plowing under. The cover crop grows 
 successfully, sometimes, if sown at the time the land is leveled off, 
 preceding harvest, and the furrowing out and irrigating of the land 
 postponed until the harvesting operations are over. 
 
 Figure 15 shows a good crop of yellow sweet clover (M. indica) 
 ready to turn under in late March, while Fig. 16 shows a similar cover 
 crop being plowed deeply after first laying the clover down with a 
 drag. Cover crops are occasionally disced under, as shown by Fig. 17. 
 This is not so desirable as deep plowing, because it does not incorpo- 
 rate the organic matter in the soil mass so closely to the tree roots. A 
 cover crop disced under improves the physical condition of the surface 
 soil, but it does not supplement the nlant food of the soil so much as 
 though it were plowed under. 
 
186 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 IRRIGATION 
 Before discussing the irrigation of any crop, it is well to understand 
 the extent and distribution of the root system of the crop in question. 
 It is a commonly held opinion that walnut trees are very deep-rooted 
 when grown on the majority of the orchard soils of southern Cali- 
 fornia. There are exceptions to this general rule, but in the deep 
 friable soils of the typical walnut sections the problem usually is 
 not how deep do the roots go but where do they stop? In treating 
 the matter of irrigation, the following discussion may be taken to 
 apply to the volume of soil included in the first eight feet from the 
 
 r v ■ 
 
 mm I >*.%%"• 
 
 
 
 
 • ** - 
 
 m 
 
 'M^n^titum *** j£T **■* .»> **<Sik^ * * ' 
 
 ^ ' ' ~ 
 
 
 A -v. : *-!rA 
 
 
 EKflfe^£^^»v* 
 
 
 Fig. 15. — A cover crop of yellow sweet clover (M. indica) ready to plow under 
 in late March. 
 
 surface of the ground. The discussion is confined to this depth of 
 eight feet, not because it is judged that this is necessarily the absolute 
 limitation of the root system, but because observations have shown : 
 first, that the root-feeding area in many groves extends to at least this 
 depth ; second, that first-class crops can be grown when only the first 
 eight feet of soil are considered; and third, if more of the walnut 
 growers observed and frequently examined this volume of soil, they 
 might be able to improve their irrigation practice. 
 
 From early spring until harvest, it is essential to have adequate 
 soil moisture available throughout the root zone, if a good tonnage 
 of well-filled, heavy-shelled, well-sealed nuts is to be produced. 
 
 In discussing the practical use of irrigation water in producing 
 walnuts, perhaps the subject can be most clearly presented if the water 
 
Bulletin 332 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 187 
 
 requirements of the crop are considered from the beginning of the 
 growing season in the spring, through the summer and harvest seasons, 
 and on to the following spring. 
 
 Fig. 16. — Method of turning under cover crop by means of a tractor and a 
 mould-board plow, after the cover crop has been laid down with a drag. 
 
 Unlike most other fruit crops, the walnut is grown for the seed of 
 the plant instead of for any edible, fleshy portion which surrounds 
 the seed. Experience in growing stone fruits, such as peaches, shows 
 
188 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 that the size of the fruit may be greatly influenced by irrigation 
 water applied late in the seasonal growth of the fruit, long after the 
 pit has hardened. This late increase in the size of the fruit is caused 
 by the increased thickness of the fleshy or edible portion of the fruit, 
 without any increase in the size of the pit itself. The growth of the 
 walnut compares with the growth of the pits of the stone fruits, all 
 of which reach their full size long before harvest and before the shell 
 is fully hardened. The walnut shells of most of the varieties begin 
 to harden about the middle or last of June. Therefore any cultural 
 or irrigation practice which is intended to affect the size of the nut 
 must take place before that time. 
 
 
 !SjJ|| 
 
 •'";.' 
 
 fa- '# *1MT 
 
 iff 
 
 Si 
 
 
 £&&hi 
 
 
 i IBBm 
 
 
 A%|| 
 
 : ''''' : *" ' 
 
 
 
 ' ■• ' - ? * •? 
 
 ■v 
 
 
 
 
 * 
 
 HraHHMHill^^SfllHHHIHIMHIBMHiH^^MHiHsi 
 
 
 "- A *i ■ • -~i .'. ■ ' 
 
 Fig. 17. — Discing a cover crop under improves the physical condition of the 
 surface soil, but it is probably not so advisable as plowing it under deeply, thus 
 bringing it in closer contact with the surface roots of the trees. • 
 
 The effect of early irrigation of walnut trees upon the size of the 
 nuts was shown on the experimental plots in Hemet, where the Experi- 
 ment Station and the California Walnut Growers' Association Field 
 Department have been investigating the causes of die-back of walnut 
 trees. In these trials, Plot A received 5.7 acre inches per acre more 
 winter irrigation than Plot D. They were otherwise handled the same. 
 In both cases, summer irrigation was commenced in the middle of 
 June. The abundance of early soil moisture from the winter irriga- 
 tion in Plot A produced a quick growth of sizable nuts, while the 
 deficient early moisture in Plot D prevented the nuts from developing 
 to normal size. The average size of a sample of the nuts from Plot A 
 was 23 per cent larger, 11 per cent heavier, and they contained 27 
 
Bulletin 332] WALNUT CULTURE IN CALIFORNIA 189 
 
 per cent more edible kernels by weight, than the average of Plot D. 
 The curves showing the volume measurement of the nuts from the 
 respective plots, expressed in cubic centimeters, is shown in Fig. 18. 
 The application of winter irrigations in the southern counties as 
 a preventive of winter injury to the trees will be more fully developed 
 later in this section. This winter irrigation serves also to supply 
 needed early spring moisture for the growth of the trees. Aside from 
 the small amount of moisture transpired by the dormant trees and 
 lost through the surface evaporation of the soil, the big bulk of the 
 
 Cubic centimeters. 
 
 13 5 7 9 11 13 15 17 19 12 
 
 i i 
 
 45 
 
 t» 
 J 40 
 
 m 35 
 
 03 
 
 ft 30 
 
 1 25 
 o 20 
 | 15 
 
 5 
 
 i ^y 
 
 Plot D. Plot A. 
 
 Fig. 18. — Showing the variation in size of 150 nuts each, from Plot D and 
 Plot A (Hemet). The latter was winter irrigated 5.7 acre inches per acre more 
 than the former. 
 
 winter irrigation water is available for the trees' use in the spring, 
 providing it is not largely used by cover crops or weeds before the 
 trees begin to grow. During seasons of normal rainfall this irrigation 
 may not be needed in the coastal districts from Saticoy northward to 
 Santa Kosa, but during seasons of light rainfall, especially in the 
 inland districts, it will increase the percentage of No. 1 nuts in most 
 years. A grove being thoroughly winter irrigated is shown in Figs. 19 
 and 21. (The illustrations are presented primarily to show different 
 methods of applying water.) 
 
 The relation of the winter rainfall and of the consequent early 
 spring soil moisture to the grade of the walnut crop the following 
 season, is shown in Fig. 20. 
 
 ~ ~ r 1 1 1 
 
 1 1 
 
 
 — 1 1 * 
 
 ^ 
 
 " A ^/ 
 
 
 . 
 
 1 
 
 
 
 
 1 
 
 f\ 
 
 
 
 / 
 
 / \ 
 
 
 \ 
 
 1. 
 
 / V 
 
 
 \ 
 
 1 
 
 / 1 
 
 / \ 
 
 1 \ 
 
 \ 
 
 / J 
 
 
 \ 
 
 \ \ 
 
 / / 
 
 
 1 
 
 v^\ - 
 
190 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 The curves are projected on a percentage basis. The base line 
 marked 100 in the left-hand margin may be taken to represent the 
 average of the normal rainfall of the following stations : Los Angeles, 
 Santa Barbara, Pomona, and Tustin. At the same time, it represents 
 the percentage of No. 1 nuts sold by the California "Walnut Growers' 
 Association in the total volume handled during the six years noted. 
 The dotted line shows the fluctuation of the percentage of seasonal 
 (July to June) rainfall, ending June 30, for the respective years 
 indicated on the bottom margin. The solid line represents the fluctua- 
 tion of the percentage of No. 1 nuts handled by the same Association 
 during the respective years, expressed as a per cent of the grade of 
 No. 1 nuts for the total six years' crop. 
 
 Fig. 19. — If the water will move into the soil readily the use of deep furrows 
 and the wetting of as little of the surface soil as possible will reduce the moisture 
 loss by evaporation to a minimum. 
 
 Although the curves may not be considered parallel, they do tend 
 to move in the same direction, except during the year 1917-18. There 
 are many factors besides total rainfall which operate to affect the 
 soil moisture available for tree and crop growth during the early 
 spring. Among these are distribution, amount per storm, weather 
 conditions between storms, and season of rainfall, together with the 
 demands upon the moisture by cover crops in many cases. These may 
 all bear more or less upon the percolation of the water into the soil 
 and thus, finally, the amount available to the walnut tree. Again, 
 
BULLETIN 332] WALNUT CULTURE IN CALIFORNIA 191 
 
 many walnut growers practice winter irrigation. In such cases, the 
 volume of rain may not be a limiting factor. It is hardly to be 
 expected, then, that the lines would be parallel during the entire 
 period ; the fact that they tend in the same direction the majority of 
 the seasons represented is unmistakable. The fact that the lines cross 
 between 1917 and 1918 may be due to the especial effectiveness of 
 the small volume of rain in 1918 in percolating deeply into the soil. 
 During the 1917-18 rainy season, the rains came late and extended 
 over a short period, percolating to practically twice the depth in the 
 
 160 
 150 
 140 
 130 
 
 - \ 
 
 - \ 
 
 — i 
 
 ) ■ 
 
 i i .1 — I — 
 
 120 
 
 - 
 
 
 \ 
 
 110 
 
 
 
 .-- 
 
 — •-. V. 
 
 100 
 90 
 80 
 
 
 
 \ ■ 
 
 70 
 
 ■ 
 
 i 
 
 . 1 1 
 
 
 1914 
 
 1915 
 
 1916 1917 1918 19 
 
 Rainfall (percentage of normal.) 
 
 No. 1 Nuts (percentage of six-year 
 
 average per cent grade J. 
 
 Fig. 20. — Expressed in percentages. 
 
 same soil as the 1918-19 rains. During 1918-19 the periods between 
 rains were characterized by northerly winds and low humidity, making 
 the rains much less effective than in the previous year. The trees may 
 have made use of nearly twice as much natural moisture during the 
 season following the 1918 rains as during 1919, owing to its distri- 
 bution over a shorter season during the former year. 
 
 The chief thing that ma3 r be learned from this is the value of soil 
 moisture in the early spring in producing large nuts. If this is a 
 correct analysis of the facts presented, the practice of winter irriga- 
 tion of walnut groves, which is followed to a great degree in some 
 districts, should become a universal practice during winters of scanty 
 rainfall. ' 
 
192 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 If the winter rains plus the winter irrigation do not percolate to 
 a depth of eight feet during the winter and late spring, it is advisable 
 to apply the first spring irrigation sometime in April. At this season 
 of the year the trees are leafed out and the young nuts should be 
 rapidly increasing in size. Filling the subsoil with moisture at this 
 season makes a reservoir for the tree roots to draw upon during the 
 early part of the summer, while the nuts are reaching their full size. 
 
 The soil moisture due to early spring irrigation, winter rains, and 
 winter irrigation, should be supplemented by water applied in mid- 
 summer to promote the growth of well-filled nuts with plump kernels. 
 This may require three applications of water in June, July and 
 August, respectively; or possibly only the first and last month men- 
 tioned, according to the type of soil and the climatic conditions. The 
 light sandy soils will require more frequent irrigation than the heavier 
 soils, while the walnut groves in the hot inland valleys will require 
 more water than those on the coast, which are frequently bathed in 
 heavy fogs and where the daily temperature is relatively low. De- 
 tailed directions for the irrigation of walnut groves cannot be pre- 
 sented in a general treatment of an industry which is found under 
 such widely divergent conditions. Emphasis should be laid, however, 
 upon the need of a continuous supply of soil moisture from the time 
 the tree leafs out in the spring, up to and including the beginning 
 of the harvest period. Just as the early spring moisture is essential 
 to the production of large nuts, and the midsummer water to the full 
 development of the kernels, ample soil moisture in early September 
 is necessary to promote the normal development of the nut to the 
 point where the husk cracks open and the nut drops free to the ground, 
 leaving the husks temporarily attached to the twigs. The absence of 
 sufficient water during the final development of the crop is almost 
 invariably associated with the sticking of the husks to the nuts, sun- 
 burning, and a consequent high percentage of cull nuts. The shells 
 of the nuts which crack out of the husks naturally, are mostly bright 
 amber color and free from stains, while those to which the husk 
 adheres are often stained, and may even be classified as culls, if the 
 stain is too deep to be obliterated by the bleaching at the packing 
 house. The cracking of the hulls when plenty of late summer water 
 is applied is of the same nature as the splitting of prunes when the 
 trees are watered as the crop is ripening. 
 
 It should therefore be the aim of the walnut grower to keep all the 
 soil from the surface to a depth of eight feet well supplied with 
 moisture from early spring until early fall. 
 
Bulletin 332] 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 193 
 
 It is a common observation of practical walnut growers that it is 
 more difficult to obtain deep percolation of the irrigation waters in 
 midsummer than in spring. This condition may be largely due to the 
 fact that subsoils are allowed to become too dry before irrigation in 
 midsummer. This excessively dry soil resists the entrance of moisture 
 to a much greater degree than does a soil which is moderately damp 
 at the time irrigation water is applied. This phenomenon of the move- 
 ment of soil moisture into soils of different moisture content has been 
 observed many times, both in the laboratory and the field. 
 
 Warn 
 
 • 
 
 
 L * ■ 
 
 jf 
 
 . -. ... ,..., v ! . "...„. 
 
 
 - 
 
 J . ■ -- . 
 
 
 
 
 ' 
 
 
 | 
 
 
 
 8 
 
 Fig. 21. — This system of the dike and check furrow irrigation is used to prevent 
 "run off" and obtain a deep moisture penetration. 
 
 Field observations on plots D and E of the Hemet irrigation experi- 
 ment harmonize with laboratory studies which have been made of 
 this subject. The sandy loam subsoil (fourth to seventh foot, inclu- 
 sive) of D was extremely dry (practically the hygroscopic point) as 
 early in the season as May 1, while the same volume of subsoil of plot 
 E reached onl} T a dryness which might be considered in harmony with 
 good irrigation practice (somewhat above the point where most annual 
 plants would wilt) by the first of June. The plots are adjacent to each 
 other and were both irrigated in the same manner and given the same 
 amount of water during June, namely, 4.2 acre inches per acre. The 
 average penetration of the same amount of irrigation water applied 
 on these two plots was as follows: D, 53 inches; E, 84 inches. Figure 
 21 illustrates an orchard being irrigated by the dike and check-furrow 
 system. This prevents "run-off" when a large volume of water is 
 used and secures a deep moisture penetration. 
 
194 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 The lesson which may be learned from the above or similar obser- 
 vations points to the necessity of applying irrigation water before the 
 subsoils become excessively dry, if a deep penetration of the water is 
 desired. Just when this time arrives depends upon the cultural and 
 irrigation practice which has prevailed during the winter and early 
 spring. If the land has not been winter irrigated, or if a cover crop 
 has been grown without adequate water, the subsoil may already be 
 dried out below the wilting point by April 1. It is impossible to lay 
 down any hard and fast general rule without examining the soil, and 
 this brings us to the next point we wish to make : Every walnut grower 
 should study and frequently observe the moisture condition of the 
 subsoil as well as the surface soil in the walnut grove. 
 
 The subsoils can be examined and readily sampled by means of 
 a soil auger. Such a tool can be made by any blacksmith and may 
 consist of a two-inch carpenters' auger, welded to a steel rod, or a 
 half-inch gas pipe. For the intelligent irrigation of a deeprooted 
 crop like walnuts, a soil auger is as much a necessary part of the 
 equipment as an irrigators' shovel. 24 Opposite sides of a given ten- 
 acre tract may take water quite differently in the subsoil, while the 
 surface soil seems uniformly irrigated. Only by the use of a soil 
 auger can the farmer make any more than a poor guess at the soil 
 moisture conditions throughout the deep root zone of the walnut tree. 
 Figure 22 shows a farmer examining the subsoil in his grove to a 
 depth of 8 feet, for the first time. Enough was learned from this 
 one examination to convert him to the use of the auger henceforth. 
 
 The amount of water necessary to wet down through the root zone 
 in a walnut grove will depend largely upon the type of soil and the 
 degree of dryness which prevails before the water is applied. In gen- 
 eral, it will require from l 1 /^ to iy 2 acre inches per acre for each foot 
 depth of soil, to bring the moisture from the wilting point or below, 
 up to the normal field moisture-holding capacity of the soil. This 
 may be taken as only a very general rule, however, as a clay loam 
 soil which has been allowed to become very dry may require more 
 than the above, while a sandy loam only moderately dried will require 
 less. In any case, the farmer should study closely the movement of 
 the irrigation waters in his own soils. 
 
 If, for example, he wishes to apply water enough on a sandy loam 
 soil to penetrate downward 8 feet from the surface, it may require 
 10 acre inches per acre (1*4 X 8 = 10) if the subsoil is dry, as well 
 
 24 A soil auger has been designed by the Orchard Management Division, and 
 is sold to walnut growers at cost by the California Walnut Growers' Association. 
 
Bulletin 332 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 195 
 
 as the surface soil, at the beginning of the irrigation run. On the 
 other hand, 6 acre-inches may be ample if the subsoil is not excessively 
 dried. On land underlaid by clay or gravel within 8 feet from the 
 surface, there is a likelihood that the root zone is correspondingly 
 shallower than in the preceeding example. 
 
 Fig. 22. — A farmer examining the subsoil in his grove to a depth of 8 feet. 
 
 If the distribution of the root system of a crop justifies the practice 
 of applying water sufficient to wet down to a depth of 8 feet, such a 
 use of water at infrequent intervals will be more economical than 
 frequent shallow irrigations. In the former case a smaller percentage 
 of the total water applied will be lost by surface evaporation in the 
 first 8 or 10 inches of soil. The frequency of irrigations desirable 
 will depend upon the age and the number of trees per acre, the soil 
 
196 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 type, the presence of intercrops, climatic conditions, etc., all of which 
 comes back again to the necessity of each farmer ''going to the bot- 
 tom" of his own soil conditions with a soil auger. 
 
 Measurement of the water applied (explained on page 150) is as 
 important as studying its movement through the subsoils to the 
 farmer who wishes to learn the most about the moisture conditions of 
 his soil and to improve his knowledge of the use the walnut trees are 
 making of the water applied. It may prove a greater mistake in the 
 end to apply too much water than not to apply enough. "Water 
 applied in excess is lost in the country drainage and may contribute 
 to the rise of seepage water, to the eventual detriment to lands lower 
 down, if not to the land in question. This may seem a far cry to 
 many people who own groves where the ground water is now 30 to 
 50 feet from the surface. Such a rise of ground or seepage waters 
 has occurred, however, through many valleys of the West where the 
 ground waters were formerly 30 to 40 feet from the surface. Much, 
 of course, depends upon the nature of the deep soil formations. It 
 is sufficient now to say that the farsighted intelligent irrigator who 
 looks upon his walnut grove as a permanent investment, will study 
 the movement of soil moisture, not only throughout the root zone, 
 but farther, and inquire into the possible loss of water by deep perco- 
 lation beyond the reach of the walnut trees. 
 
 The actual method of applying the water to the soil must be 
 adapted to the conditions of each case. Three different systems of 
 applying water are illustrated by Figs. 19, 21, 23, 24, and 25. The 
 advantages of the respective methods are briefly stated under each 
 illustration. 
 
 INTERCROPPING 
 
 Intercropping the young walnut groves is a practice which pre- 
 vails in a large majority of cases. This practice has usually proved 
 very successful in making the land support the orchard before the 
 walnuts come into profitable bearing. 
 
 . The best intercrop to use will depend somewhat upon local circum- 
 stances. In the bean districts and in cases where the walnut groves 
 are large enough to justify the maintenance of bean farm machinery, 
 beans are an ideal intercrop for the young walnut grove. The bean 
 is a legume and requires thorough cultivation. These facts contribute 
 to the best conditions for the development of the young trees, if suf- 
 ficient irrigation water is avaialble for both crops. The bean straw 
 can be plowed under, which is an advantage of the bean intercrop 
 over all others. 
 
Bulletin 332] 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 197 
 
 
 y S&i@mH&nH 
 
 
 
 
 
 
 
 ^■?8P^* WfSSf^ J * ~- aV 
 
 
 
 F^ 
 
 V.'^^ , *»i5 
 
 
 i£wr' ■".■ftr, i^lMflW -^ PP^ ""• •"' ~ !£iL 
 
 
 
 
 SBP^^'"' 
 
 . , *<■; v?j 
 
 .«- 
 
 -T ; "-Y 
 
 sHSl^^^ 8 *^' 
 
 
 
 
 Fig. 23. — The furrow system is probably the most advisable way of applying 
 water, if the water will move into the subsoil readily and the surface slope is such 
 that it flows across the orchard satisfactorily, and without much ' ' run-off. ' ' 
 
 Fig. 24. — If the land is check-furrowed at the lower half of the orchard, the 
 run-off will be reduced and added pressure of deeper water in the furrow forces 
 the moisture into the dry subsoil. 
 
198 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 Outside of the bean districts, the choice of intercrops largely 
 depends upon the market conditions for the proposed crops. Several 
 of the vegetables commonly grown for canning factories may be profit- 
 ably grown in the young orchard without harm to the trees. Such 
 crops as tomatoes, peppers, and string beans are often used. Figure 26 
 illustrates a bean intercrop in a bearing walnut grove. 
 
 Intercrops of corn, milo, squashes, and pumpkins are not so well 
 thought of among many experienced walnut growers, because of their 
 apparently harmful effect upon the trees. Milo especially is generally 
 considered a bad intercrop for walnuts. Milo is a very drought- 
 resistant crop with a relatively low water requirement. It will there- 
 fore develop a first-class crop under soil conditions unfavorable to 
 the best growth of the walnut trees. The thrifty appearance of the 
 milo may deceive the farmer concerning the condition of the walnut 
 roots. Only the closest students of irrigation should attempt to grow 
 this crop in a walnut grove, and it may be of doubtful value even 
 then. 
 
 If the grower has only a small plantation, not justifying the 
 maintenance of bean farm machinery, and has not a ready market for 
 a vegetable crop, the intercropping with a precocious bearing fruit tree 
 may be desirable. Peaches, prunes, and apricots are among the fruit 
 trees most commonly used in such schemes of intercropping. In many 
 instances observed, the growing of these stone fruits in a young walnut 
 grove has retarded the growth of the nut trees, when compared with 
 groves interplanted with beans. Nevertheless, in many cases, the 
 fruit trees have been profitable and have made the orchard self- 
 supporting while the nut trees were growing, thus out-weighing, from 
 a business point of view, the temporary check of the walnut trees. 
 If fruit trees are used as an intercrop, the farmer must study his 
 irrigation problem carefully to be sure the walnut trees are not robbed 
 of their needed water by the companion crop. General observations 
 indicate that the apricot tree is a keener competitor of the walnut 
 than the peach, and thus less suitable to plant. 
 
 The disadvantages of intercropping the young walnut grove with 
 fruit trees should be considered before laying out a plantation in 
 this manner. The following are among the most serious objections. 
 If the cling-stone canning peaches are used as an intercrop, they will 
 require late summer irrigation to fully develop their crop, after water- 
 ing should be discontinued upon the walnuts. This discordant water 
 requirement will be most troublesome when the plantation is from 
 three to six years old. At this period the owner is naturally anxious 
 
BULLETIN 332] WALNUT CULTURE IN CALIFORNIA 
 
 199 
 
 Fig. 25. — Basin irrigation, with water standing six or seven inches deep over 
 the land, insures its movement into the subsoil. This is especially practical on 
 the level sandy soils. This system may also be used to advantage where the surface 
 soils are very sandy and thus take water so rapidly that it is impractical to force 
 a small stream in a furrow across the orchard. 
 
 Fig. 26. — Showing beans used as a profitable intercrop in a ten-year-old grove, 
 in a bean-growing district. 
 
200 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 to make the most of the first commercial peach crops, and some of 
 the latest and most profitable varieties should be watered in late 
 August and September in order to bring them to a good size for the 
 canning factory. This late water on young walnut trees is very liable 
 to keep the twigs growing so late that they will be severely injured 
 by the early fall frost. Such a hazard will diminish as the walnut 
 trees come into bearing and the drain of crop production acts as a 
 regulator in slowing up the late summer growth and in thus aiding 
 the walnut trees to become nearly dormant at the season of early fall 
 frosts. The prune has been a profitable intercrop with walnuts, but 
 here the discordant water requirements are somewhat reversed, and 
 do not become pronounced until both the prunes and the walnuts are 
 in bearing. At this stage in the development of the plantation, when 
 it is possibly from six to twelve years old, and before it seems econom- 
 ically sound to pull out the prunes, the late summer water require- 
 ments are quite opposite with these two crops. As the walnuts mature 
 they should be irrigated so that they will be fully developed and so 
 that the husks will crack open, producing a clean-shelled, plump- 
 kerneled nut ; irrigation of the prunes at this time will also cause them 
 to crack open and in so doing make an inferior product, liable to 
 rejection by the prune-selling agencies. 
 
 If either prunes or peaches are used as interplants it would seem 
 advisable to plant the walnuts 30' X 60' and the fruit trees in solid 
 rows in the middle of the interspaces. These temporary trees might 
 be planted only 15 feet apart in the row, which would give enough 
 fruit trees per acre to make it worth while, and yet have room enough 
 for heavy fruit production for a few years in this rather "hedge- 
 row" planting. The following diagram illustrates this plan. 
 
 p 
 
 X O X 
 
 O Permanent walnut trees. 
 X Temporary walnut trees. 
 P Filler trees of peaches or prunes. 
 
 This arrangement would permit irrigating only a part of the land 
 and thus serving the water requirements of one crop without affecting 
 
Bulletin 332] WALNUT CULTURE IN CALIFORNIA 201 
 
 its associate crop, or only slightly. As the trees grow older, the roots 
 become interwoven throughout the entire soil mass and gradually the 
 advantages of this plan lessen, and the filler trees should then be 
 pulled out. 
 
 FEBTILIZATION 
 The walnut crop makes relatively small demands upon the plant 
 food of the soil in comparison to other fruit crops. This may be illus- 
 trated by Table VII. 
 
 TABLE VII 
 
 Plant Food Elements Withdrawn from the Soil by Various Fruits, 
 Expressed in Pounds per Acre 
 
 Phosphoric 
 Fruit Amount of crop Nitrogen acid Potash 
 
 Oranges 16,300 lbs. 28.23 lbs. 8.63 lbs. 34.39 lbs. 
 
 Lemons 18,900 lbs. 28.53 lbs. 11.52 lbs. 50.84 lbs. 
 
 Apricots 10,000 lbs. 19.73 lbs. 6.40 lbs. 29.00 lbs. 
 
 Walnuts 1,000 lbs. 10.20 lbs. 2.78 lbs. 1.50 lbs. 
 
 Very little definite information has been obtained on the subject 
 of fertilizing walnuts since Smith 25 reported in 1912 the results of 
 the fertilizer trials on the Cudahy ranch. In reviewing these results 
 the author wrote as follows : 
 
 The results of this experiment are typical of all experience in fertilizing- 
 walnuts. Many attempts have been made to determine the most effective 
 practice in this respect, but all of these have shown no positive effect on 
 account of variation in the trees and an apparent lack of response to fertilizers. 
 In regard to walnut fertilization it is, therefore, impossible to offer definite 
 advice based on actual experiments, but the most that can be done is to suggest 
 such practice as may reasonably be expected to give good results with any 
 crop on California soils. We know in general that nitrogen and phosphoric 
 acid are our most needed elements and that the application of these substances, 
 especially on older plantings, is almost certain to result in improved growth 
 and vigor in almost any plant. We also know of the walnut, that individual 
 trees produce as a general rule, ip proportion to their size, and that the larger 
 they become the greater crops they will bear. It is, therefore, our conclusion 
 that in fertilizing walnuts, nitrogen and phosphoric acid should be the elements 
 most largely supplied. 
 
 Along with fertilization there should not be forgotten the importance of 
 keeping the soil in good mechanical condition, especially in order that it may 
 absorb and retain the greatest possible amount of moisture. Indeed, it is 
 evident from the results of the Cudahy experiment, as well as from general 
 observation, that this factor is much more important, at any rate for several 
 years, than that of fertilization. 
 
 25 Walnut Culture in California, Univ. of Calif., Experiment Station Bull, 
 No. 231, 1912, p. 188. 
 
202 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 Field trials with various kinds and amounts of fertilizers applied 
 to several walnut groves are now being carried on by the University 
 of California, cooperating with the field Department of the California 
 Walnut Growers' Association. Although these trials have been in 
 progress since the fall of 1917, definite conclusions cannot be drawn 
 from this work at the present writing. 
 
 With the widely varying soil conditions which exist in the several 
 walnut-growing districts, a uniform fertilizing program is not likely 
 to be suitable to all. To be profitable, however, the excess due to the 
 fertilizers must pay the added cost of the fertilizer, the labor of apply- 
 ing, and the labor of handling the increased crop. Each farmer should 
 make a careful study of any fertilizer treatments applied to his own 
 grove, in order to be able to judge of the economic soundness of 
 fertilizing walnuts under his local conditions. 
 
 PRUNING 
 
 Unlike many of the fruit trees, such as apples, or oranges, the 
 pruning of the walnut tree has not evolved into a very definite, sys- 
 tematic practice. In many groves no pruning at all is done except 
 the cutting off of the lower limbs which interfere with cultural 
 practice. 
 
 The fact that few walnuts are produced in the centers of the old 
 trees, has suggested a moderate thinning out of the branches from 
 year to year in an attempt to promote production more uniformly 
 throughout the trees. Sunlight is necessary for the production and 
 maintenance of fruit spurs, and, without some thinning out, prac- 
 tically all of the crop is produced on the outside twigs, in the tops, 
 and on the sides of the trees. Some of the most successful walnut 
 growers have adopted this sort of pruning as an annual practice, 
 cutting out the water sprouts and the dead wood; thinning out the 
 thickest growing portion of the top, and reducing the number of 
 crossed limbs and weak crotches. In the absence of any results of 
 systematic field trials this gradual and annual thinning-out process 
 seems the most advisable. 
 
 This system of pruning should not include the heading back of 
 the fruiting limbs, as such a practice will promote a rapid growth of 
 water shoots near the ends of the parts which remain, defeating the 
 very attempt to shorten the limbs. If the limbs are too long and 
 top-heavy on the sides of the trees, they should be cut out entirely, 
 or cut off to lateral limbs, thus restricting in a measure the develop- 
 ment of water shoots. 
 
Bulletin 332] WALNUT CULTURE IN CALIFORNIA 203 
 
 In all pruning operations with the walnut, care should be taken 
 to cut the limbs off smoothly with a saw without leaving any stub. 
 All wounds of 2 inches in diameter or over should be painted with a 
 weatherproof paint. The walnut wood decays very readily and there- 
 fore any large cut exposed to the weather for a short period will 
 surely become infected and start a decay which will eventually spread 
 to the center of the tree. The framework of the tree thus undermined 
 by so-called heart rot, may be split by an overload of nuts, and par- 
 tially or wholly destroyed. 
 
 It is expected that the pruning experiments now being carried 
 on by the University of California in cooperation with the Field 
 Department of the California "Walnut Growers' Association will event- 
 ually give definite information on this subject. 
 
 INSECT AND DISEASE PESTS 
 
 Insects. — The only insects which are troublesome to the walnut 
 industry are the codling moth, the aphis, and the red spider; these 
 are mentioned in their probable order of importance. 
 
 Codling Moth mid Aphis. — These two insects may well be con- 
 sidered at the same time, for, where they both occur, control methods 
 for both may be combined in one application. 
 
 The codling moth has been known to attack walnuts in California 
 since 1909, when it was first observed in the vicinity of Concord. 20 
 Since its first appearance, it has periodically become very troublesome 
 in several of the walnut districts of southern California. 
 
 The injury caused by the codling moth to walnuts is similar to 
 that seen in wormy apples. The worm eats a portion of the kernel 
 of the nut and renders the remainder uneatable. The manner of 
 attack and entrance of the worm is clearly shown in Fig. 27. 
 
 The aphis is a small green plant-louse which feeds on the leaves 
 and succulent growth by sucking their juices. This weakens the tree 
 at a critical stage, causes it to produce less crop, lighter and smaller 
 nuts, and imperfect shells. The foliage of a tree infected with this 
 insect becomes covered with ''honey dew," a sticky secretion which 
 turns black upon continued exposure to the air. The damage caused 
 by the aphis varies from year to year. In some sections the damage 
 is considerable every year, in others only in exceptional years. The 
 aphis usually disappear with the approach of extremely hot weather. 
 
 26 The Codling Moth in Walnuts. H. J. Quayle, Monthly Bull., Dept. Agric. 
 California, vol. IX, No. 3, 1920, p. 64. 
 
204 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 In discussing the control of the codling* moth and aphis before 
 the Third Annual Convention of the Walnut Growers at Whittier, 
 California, in January, 1920, Professor H. J. Quayle of the Citrus 
 Experiment Station made the following recommendations : 27 
 
 THE CONTROL OF THE CODLING MOTH ALONE 
 
 Where the codling moth has been present in orchards in past years and the 
 amount of infestation has been about 5 per cent or greater, the trees should 
 be dusted or sprayed with basic arsenate of lead between May 25 and June 20. 
 
 1. Busting. — Five or six pounds of dust 28 per tree is required for trees of 
 medium size, and 7 to 10 pounds for the largest trees. A thorough application 
 should be made to cover all the nuts on all parts of the tree. 
 
 2. Spraying. — Use 6 pounds of dry basic arsenate of lead to a 200-gallon 
 spray tank. For trees of average size, 20 to 25 gallons of the spray per tree is 
 necessary, or % of a pound per tree of arsenate of lead. For the largest trees, 
 30 gallons per tree of spray is necessary, or % of a pound of arsenate of lead 
 per tree. All the nuts on the trees should be reached by the spray. It is not 
 necessary to spray the trunk and branches or any pare of the tree where there 
 are no nuts. Spray guns should be used in order to reach all parts of the tree. 
 Spraying will insure a higher degree of control of the codling moth than dust- 
 ing, but the labor expense is somewhat more and it takes longer to cover a 
 given acreage. 
 
 FOR APHIS AND CODLING MOTH 
 
 Where past experience has shown that the walnut aphis, as well as the 
 codling moth, may generally be present in large numbers, use a dust combina- 
 tion containing both tobacco and arsenate of lead. If spraying is to be prac- 
 ticed instead of dusting for the codling moth, add one pint of "black-leaf 
 forty '' to each 200-gallon tank of arsenate of lead. 
 
 FOR APHIS ALONE 
 
 Where there is no codling moth, but the aphis is generally present in 
 serious numbers, use Nico-dust, a material especially prepared for aphis control. 
 From 2 to 6 pounds of this material is necessary per tree, according to the 
 size of tree. The best general time for such treatment is during the last week 
 of May and the first two weeks of June. During years when the aphis occurs 
 in great numbers, it may be advisable to dust a second time, during July or 
 August. 
 
 RED SPIDER 
 
 In some years the red spider does much damage to walnut trees in isolated 
 instances. Injury is not usually apparent until the middle of the summer, 
 when the leaves turn a dull but decided yellowish hue. A close examination 
 at this time will show the presence of a countless number of red spiders, barely 
 
 *7 From an unpublished manuscript. 
 
 28 Arsenate of lead is mixed with kaolin, which acts as a diluent and a carrier. 
 Use only the standard commercial brands. 
 
Bulletin 332] 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 205 
 
 visible to the naked eye. If the injury goes on unchecked, the leaves will drop 
 prematurely, injuring the quality of the current crop and the development of 
 fruit buds for the future crop. 
 
 The most practical control measure is dusting with dry sulfur and hydrated 
 lime, three parts to one, respectively. Spraying during the dormant period has 
 not been advisable in the past, because outbreaks of this insect have not been 
 frequent. 
 
 Fig. 27. (From "The California Walnut.") 
 
 (a) Appearance of green nut after worm has entered on open side, (b) Codling 
 moth worm usually enters green nut on the stem end as here shown, (c) A round 
 or oval opening on the stem end of the cured nut is almost a sure sign that the 
 worm has paid his respects inside, (d) Section of walnut showing the codling moth 
 worm. 
 
 WALNUT BLIGHT 
 
 The walnut blight is by far the most destructive disease affecting 
 the walnut crop. The prevalence of this disease, as previously stated, 
 varies considerably from year to year, and is usually much worse in 
 the foggy coastal districts than in the inland valleys. In years of 
 
206 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 bad outbreaks, the blight has probably destroyed from 15 per cent to 
 20 per cent of the crop. It is a bacterial disease which attacks the 
 young and tender growth and spreads to the more mature wood, 
 causing the affected areas to turn black and die. Under favoring 
 conditions, the disease is especially destructive to the nuts. If it 
 attacks the nuts early, it causes them to turn black and drop off when 
 one-eighth to one-half of an inch in diameter. It causes mature nuts 
 to remain undeveloped, and may make full-grown nuts unmarketable, 
 except as culls. It shows on the nut as black spots most prevalent at 
 the calyx end, but often scattered over its entire surface. 
 
 At present there is no control known for this disease. Attempts 
 to lessen the prevalence of the blight by spraying and by the com- 
 bination of spraying and pruning off the old blight cankers from the 
 twig growths, have had no measurable effect upon the disease. 29 
 
 Some of the varieties now being propagated are more resistant to 
 blight than the average seedling tree. At present the greatest likeli- 
 hood of relief from this disease lies in securing resistant or immune 
 varieties. 
 
 MELAXUMA 
 
 This troublesome disease of the walnut tree has occurred in isolated 
 and serious outbreaks in Santa Barbara, Ventura, Los Angeles, and 
 Orange counties. Careful studies of this disease were made and 
 reported in 1914 to 1915 by Fawcett. 30 The nature and treatment 
 of the trouble may best be summarized by quoting from the above 
 author. (For a detailed discussion of the disease, see the original 
 publication.) 
 
 Because of the oozing of dark watery material to the surface of the 
 affected areas, this disease is often confused, under the name of "black sap," 
 with sunburn, frost injury, injuries to the bark in cultivation, injury from the 
 decay of wood at places where limbs have been cut off, and other troubles in 
 which a "black sap" may ooze out during the active growing period of the 
 tree. It should not be taken for granted, therefore, that, because a black ooze 
 is seen on the trunk or larger limbs of a walnut tree, Melaxuma is necessarily 
 present. 
 
 As the term "black sap" has already been used by E. E. Smith to designate 
 a result of sunburning, this name was not considered suitable for the disease 
 here being considered. The word Melaxuma, derived from two Greek words 
 meaning "black" and "juice" was therefore adopted, and is now in fairly 
 common use to designate the disease herein described. 
 
 29 An Attempt to Control Walnut Blight. H. S. Fawcett and L. D. Batchelor. 
 Monthly Bulletin, California Dept. Agri., vol. IX, No. 5-6. 1920. 
 
 so Melaxuma of the Walnut, H. S. Fawcett, Univ. of Calif. Experiment Station 
 Bull. No. 261, 1915. 
 
Bulletin 332] WALNUT CULTURE IN CALIFORNIA 207 
 
 Description of the Disease 
 
 Melaxuma shows its effect most strikingly during the summer after the 
 growth is well started. On trees severely affected at this time, there will be 
 seen large black sunken cankers on the trunk and larger limbs and often a 
 sudden wilting of the smaller limbs and twigs. This sudden wilting of the 
 smaller limbs is so different from the effects of walnut blight or bacteriosis, 
 that it is easily distinguished from that disease. 
 
 The most common location for Melaxuma cankers is at the crotch of the 
 tree where the first limbs join the trunk. The first evidence of the disease 
 is often a black area on the otherwise grayish bark which looks like a dab of 
 tar, as shown by Fig. 28. This is due to the staining of the bark by a black 
 watery substance that forms under it. The diseased area later becomes slightly 
 sunken, shrinks, and cracks. The ' ' black sap ' ' then oozes out in considerable 
 quantities and stains the bark as it runs down the limb or trunk. The wood 
 underneath is discolored for a short distance and this discoloration usually 
 extends beyond the margin of the killed bark. The diseased areas, as a rule, 
 do not extend entirely around a limb in one season, but affect only about one- 
 third or one-half the circumference of the bark. Later in the summer or fall 
 the increase in the size of the areas is slower and often appears to be stopped. 
 One part of the margin of the canker may dry out and begin to heal over, while 
 the other continues to advance or remains stationary until the next spring, when 
 it begins to advance rapidly again. A few cankers on large limbs of vigorous 
 trees may even heal over without treatment. More often there is an enlarge- 
 ment from year to year which in two or more years extends entirely around a 
 large limb, causing it to wilt and die. These limbs occasionally wilt suddenly, 
 the dried-up nuts and leaves remaining attached for some time. When cankers 
 occur on the trunks they generally follow some injury to the bark made by a 
 plow, cultivator or other instruments used in the cultivation of the orchard. 
 
 From the observations and results of experiments so far made, the following 
 tentative treatment is suggested: 
 
 Cut out the cankers that have not gone too far on the trunk and larger 
 limbs and disinfect the wounds thus made. (See Fig. 29.) The dead and 
 discolored bark should be cut away, getting a little beyond the margin of dead 
 tissue. If the cankers are not large and the wood underneath has not been 
 stained deeply, it will pay to dissect all the discolored wood as well as the 
 bark. Probably one of the best disinfectants to apply to the wound is the 
 Bordeaux paste, 31 that is recommended for lemon gummosis. If the canker is 
 
 si Bordeaux Paste. The formula for Bordeaux paste is as follows: 12 pounds 
 of Milestone (copper sulfate) dissolved in 8 gallons of water in a wooden, earthern 
 or glass vessel; and 24 pounds of quick-lime slaked in 8 gallons of water. When 
 the lime is cool, stir together about equal parts by volume of each, for making 
 enough mixture to last for one day only. The Milestone is most easily dissolved 
 by suspending it in a sack at the top of the water over night. If the Milestone is 
 pulverized and suspended in warm water, it dissolves rapidly. Good lime that is 
 not air-slaked should be used, and after slaking it with the water, it should be 
 allowed to cool before being used in making paste. If covered to avoid evapora- 
 tion each ingredient will keep indefinitely, but after mixing, the paste slowly 
 deteriorates. Where it is being used over a number of days or weeks, just enough 
 of the wet slaked lime and the Milestone solution should be mixed to make paste 
 enough to last for one day, leaving the remainder unmixed in separate vessels. It 
 may be applied with large brushes, as in whitewash. 
 
208 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 large and has been in the tree a long time, the wood may be stained so deeply 
 as to render the work of cutting out all discolored wood too expensive. If the 
 canker has practically girdled the limb, the limb had better be cut out. 
 
 WINTER INJURY OR DIE-BACK 
 This trouble of the walnut tree has been made the subject of con- 
 siderable study by Smith 32 and Batchelor and Reed. 33 Perhaps it 
 can be summarized best at this time by quoting from the last men- 
 tioned authors. 
 
 Winter injury or die-back of walnuts is characterized by a sudden death 
 of the tops of the trees. Such injury is usually first noticeable during the 
 early spring following the dormant period. 
 
 The most common causes of the winter injury or die-back are given below. 
 
 1. Early autumn frosts kill the immature, growing shoots. Young walnut 
 trees are more subject to injury from this cause than older trees, because they 
 are usually later in maturing their new wood. Such frosts cause the foliage 
 to drop prematurely and injure the growing tips of the twigs. The denuded 
 twigs are subject to further injury from subsequent fall and winter sunburn. 
 The presence or extent of this injury is usually overlooked until the following 
 spring. 
 
 To reduce the danger from autumn frosts it is advisable to withhold the 
 late summer irrigation in order to promote the early maturity of the trees. 
 
 2. Winter drought causes die-back in either young or bearing walnut groves. 
 Trees suffering from this condition fail to make new growth in the spring, 
 except from the trunks or main limbs. The new growth on such trees has lost 
 so much water during the winter that the buds are unable to develop in 
 spring. The cause of the die-back has been found to be due to an extremely 
 low moisture content of the soil during a large part of the winter. Under such 
 conditions, the water lost from the young shoots during the winter cannot be 
 replenished by the root system, and the shoots die from desiccation. 
 
 Fall and winter irrigation of the walnut groves has been found to eliminate 
 the injury from winter drought. The amount of irrigation will depend upon 
 the type of soil, the amount of soil moisture present at the end of the harvest 
 season, and the rainfall which may be expected later in the season. 
 
 Figure 30 shows a walnut tree thus affected and afterward cured 
 by winter irrigation. 
 
 The late fall or early winter irrigation of the walnut groves, 
 especially in the inland valleys, may be looked upon as an insurance 
 policy against this form of die-back. To be effective it should be 
 applied in December and January. In some years subsequent rains 
 will show that the die-back insurance policy was unnecessary. The 
 
 32 R. E. Smith, Walnut Culture in California, Univ. Calif. Experiment Station 
 Bull. No. 231, 1912, p. 372. 
 
 33 L. D. Batchelor and H. S. Reed, Winter Injury or Die-back of the Walnut, 
 Univ. of Calif. Experiment Station Circ. No. 216, 1919. 
 
Bulletin 332 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 209 
 
 Fig. 28. — One of the first evidences of Melaxuma. The black sappy ooze has 
 appeared at the outer edges of the killed bark at the crotch. The bark between 
 has been killed and pycnidia of Dothiorella have already appeared on the surface 
 of part of the killed bark. (From Fawcett, Bulletin 2 til.) 
 
210 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 same apparent objection, however, applies to fire insurance on the 
 barn or house, during the years that there are no fires on the property. 
 
 3. A high water-table may be a contributing factor in die-back. A perma- 
 nently high water-table causes the trees to prolong their growing season, with 
 the result that they are killed by frosts. The sudden rise of a fluctuating water- 
 table may kill a large part of the root system and produce a typical die-back 
 in the tops, even though the wood is mature. 
 
 4. Alkali soils containing such a high salt content as to injure the root 
 systems of walnut trees, also cause the tops of the trees to die back in response 
 to the root injury. In the initial stages of alkali injury, the leaves turn brown 
 at the margin and fall prematurely. The denuded shoots sometimes put out a 
 new set of leaves in the fall. The top of the tree gradually dies back until 
 the entire tree is lost. 
 
 If injury is being caused by irrigation water containing too much 
 alkali, obviously the use of such water should be discontinued. 
 
 HARVESTING, CURING, PACKING, AND COST OF PRODUCTION 
 
 HARVESTING 
 
 During favorable seasons and in well-cared-for groves the husks 
 of the nuts crack open and adhere temporarily to the twigs, while the 
 nuts drop clean-shelled to the ground. This natural dropping of the 
 great bulk of the nuts occurs with most varieties between September 1 
 and November 7. There are usually enough nuts on the ground to 
 justify the first picking by the second week in September. The 
 natural falling of the nuts is hastened by the shaking of the trees 
 by means of long poles with hooks attached to the ends. 
 
 During the harvest period the nuts are picked up three or four 
 times before the total crop has matured and dropped. It is not con- 
 sidered good practice to allow the nuts to remain for a long time on 
 the ground. Nuts thus neglected are subject to the work of ants in 
 the kernels, and may be rained on by the autumn showers. The 
 effect of rain upon the nuts may be entirely superficial if they are 
 picked up promptly after they are dry again. At the best, however, 
 they will be dirty and more or less stained, causing extra work of 
 washing in preparing them for the packing house, and making proper 
 bleaching more difficult. Nuts long neglected on the ground after a 
 rain become mouldy and stained on the outside of the shells, especially 
 those which have a portion of the husk adhering to them. If the 
 stain of the mould is pronounced, it will be impossible to bleach it, 
 and the nut must be graded as a cull. If further neglected, the mould 
 from the outside of the nut may spread to the kernel, through the 
 base of the nut, and thus lower the value even as a cull nut. 
 
Bulletin 332] 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 211 
 
 A certain percentage of the nuts will drop with the husks adhering 
 to them. These are commonly known as ' ' stick-tights ' ' and are likely 
 to be inferior to the clean shelled nuts in their plumpness and in the 
 appearance of the kernels. There is usually a high percentage of 
 
 
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 I 
 
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 fZ**< 
 
 
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 Ws&'t- " 
 
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 ' 1 
 
 Fig. 29. — Walnut trees showing the location of Melaxuma cankers that had 
 been cut out and treated with Bordeaux paste the year previous. Notice the rows 
 of holes in the bark of one tree, made by sapsuckers. These probably served in 
 this case as a partial means of infection. (Fawcett, H. S., Bulletin 261.) 
 
 blanks, shriveled, mouldy, and dark-colored kernels among the stick- 
 tight nuts. The percentage of stick-tights is greater during seasons 
 of abnormally high temperatures, when the nuts are sunburned and 
 when the husks are affected with blight. Again, trees which suffer 
 
212 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 from drought during the latter part of the growing period, or which 
 are subject to the attacks of aphis, red spider, or for any other reason 
 lose their leaves prematurely, produce a high percentage of stick- 
 tights and inferior nuts. 
 
 In general, the stick-tight nuts are husked by hand, especially those 
 on which the husks are actually green, although several large ranches 
 have made devices to husk them by machinery. The portions of the 
 husks which have dried on the nuts, as in the case of sunburning, and 
 blighted husks, are removed by the washing machine, described later. 
 
 The nuts are usually picked up and sacked by Mexican and Jap- 
 anese families who contract to perform this work. 
 
 WASHING AND CUEING 
 
 After being picked up and sacked, the nuts are ready for curing. 
 If the majority of them are dirty from lying on the ground during 
 showers, it is necessary to wash them. This washing is done in large 
 cylindrical drums made of coarse wire netting, in which the nuts are 
 slowly revolved under a stream of water, grinding against each other 
 and against the wires which form the sides of the drum. They are 
 thus cleansed of all loose foreign material. This washing process will 
 not remove the stains on the shells due to sunburned and blighted 
 husks sticking to the nuts. There is practically no need for washing 
 the clean-shelled nuts. 
 
 The curing is accomplished by spreading the nuts out in shallow 
 trays, with bottoms made of slats spaced about one-half an inch 
 apart. The nuts should not be left exposed to the sun during the 
 entire day if the weather is especially clear and hot, for the drying 
 will be so rapid that many of the nuts will crack open. If the trays 
 are spread out in the morning and the nuts thoroughly stirred several 
 times, the trays may be piled up when the nuts are well warmed up. 
 The slow drying which goes on while the trays are in piles of course 
 prolongs the length of the process, but is good insurance against the 
 splitting of poorly sealed nuts and their rejection as culls by the 
 packers. Figure 31 shows a yard full of trays ready to be piled up 
 after being thoroughly warmed up by the morning sun. The trays 
 should be so piled up as to allow ventilation between them. 
 
 If the walnut grove is large enough, it will save expense to use 
 a "drying house" for the curing process. Such "dry houses" are 
 built with outer walls of lath to give good ventilation as shown by 
 Fig. 32. The drying bins are arranged one above another. The nuts 
 are carried away from the washing machine by a belt and thence 
 
Bulletin 332] 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 213 
 
 m ■ .$ht+ 
 
 ^r-^m^^^, ^ ~; "*» 
 
 Fig. 30. — Showing the effect of winter drouth and recovery of the tree two 
 years later after irrigation. 
 
 Fig. 31. — Drying walnuts by means of spreading them on trays placed on low 
 racks. 
 
214 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 elevated to the upper bin, as shown in Fig. 33. The nuts are dumped 
 mechanically from one bin to the bin below it. Thus the nuts work 
 through the whole series of bins from the top down. There may be 
 seven or eight of these bins and by dumping them each once a day, 
 the nuts will be passed through the house in seven or eight days. As 
 the nuts leave the bins after this period, they are usually sufficiently 
 cured to be ready to go to the packing house, to be bleached, graded, 
 and bagged for shipment. If the weather is warm and the atmosphere 
 very dry, the nuts may pass through the drying house in four or five 
 days. Much will depend also upon the condition of the nuts when 
 they go into the house, as well as upon the exposure of the house to 
 breezes, sunshine, etc. 
 
 As the nuts pass along a belt when they come from the drying bins, 
 or as they are sacked from the trays, they should be carefully sorted 
 to pick out the culls. Nuts are thrown into this cull class if they are 
 cracked, perforated, badly stained by blight or sunburn, wormy, or 
 if a part of the shuck is adhering to the shell. The good nuts are now 
 ready for the packing house, while the culls are kept separate to go 
 finally to the cracking plant. 
 
 PACKING 
 
 Although the packing and selling of the walnut crop in California 
 is quite distinct from its production, it is nevertheless desirable for 
 each grower to know how his nuts are to be graded and packed, in 
 order that he may realize more fully the importance of delivering 
 high-grade nuts to the packing house. About 85 per cent of the walnut 
 crop of California is packed and sold through the local houses which 
 are affiliated with the California Walnut Growers' Association. It 
 may therefore be proper to relate briefly the processes followed in 
 these houses in preparing the crop for shipment. Mr. W. T. Webber 
 has clearly described the stages of grading and packing in the words 
 quoted below. 
 
 ELIMINATING IMPERFECT NUTSs* 
 
 After being properly cured, the nuts are delivered to the local packing house 
 by the grower, where they are first run over a rough screen which frees them 
 from dirt and all foreign matter. From this screen the nuts pass through a 
 suction machine, a device which lifts the blank or imperfectly filled nuts over 
 a trap and allows the full-meated nuts to pass through. From the suction 
 machine the full-meated nuts pass on to an endless belt where girl cullers, 
 seated on each side, remove the ill-shapen and bad-appearing nuts. 
 
 34 The California Walnut, 1919, pp. 47-57. 
 
Bulletin 332] 
 
 WALNUT CULTURE IN CALIFORNIA 
 
 215 
 
 Fig. 32. — "Drying houses'' are built with outer walls of lath to give good 
 ventilation. 
 
 Fig. 33. — The nuts are carried away from the washing machine (shown in the 
 right background) by a belt, passing before the inspector who removes the culls. 
 Thence they are carried by the elevator, shown in the center, to the bins shown at 
 the right center of illustration. 
 
216 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 
 
 BLEACHING 
 
 The next treatment is that of bleaching. The nuts are given a bath of 
 from one to two minutes' duration by passing them through large drums par- 
 tially filled with a liquid bleaching solution, for the purpose of removing dirt 
 and stain and brightening the appearance of the shells. 
 
 From the bleaching drums they are passed over another shaker which frees 
 them from accumulated drops of the solution, and they are then elevated and 
 graded to size. 
 
 GRADING 
 
 For this process large galvanized-iron cylindrical graders are used. Each 
 grader is 10 feet long and 40 inches in diameter, set on a 6-inch pitch and has 
 a capacity to properly grade one and one-half tons of walnuts per hour. A 
 soft-shell walnut grader contains somewhat over 8000 li£ 2 incn square openings 
 and the walnuts which pass over the grader without falling out at one of these 
 openings are known as No. 1 Grade. Those which fall out comprise the No. 2 
 Grade. 
 
 Budded graders contain somewhat less than 8000 1% 6 inch square openings, 
 and the nuts passing over constitute the Fancy Grade and those falling through 
 the Standard Grade. 
 
 From the grader the walnuts again pass on to a grading-belt, where those 
 that have not been bleached properly, or have been broken by the bleaching 
 and grading operations, are removed. The perfect nuts then go into the drying- 
 bins, and after a period of from 24 to 48 hours are packed, 100 pounds net 
 weight, in burlap bags, ready for shipment. 
 
 THE STANDARD FOR FIRST-GRADE NUTS 
 A nut is considered satisfactory if its size is in accordance with the speci- 
 fications for the No. 1 or the No. 2 grade; if its kernel is plump and sound, 
 not too dark in color; if it is not wormy, mouldy, or rancid; and if one portion 
 of the shell has not split and fallen away from the other. The shell must have 
 no material outward blemish and must show a clean bright color. 
 
 In most seasons the California Walnut Growers' Association guar- 
 antee that at least 90 per cent of the nuts in each sack sold by them 
 comply with the above standard. 
 
 SELLING THE CROP 
 As noted heretofore, about 85 per cent of the walnut crop is sold 
 by the California Walnut Growers' Association. This central organ- 
 ization is a non-capital, non-profit, cooperative association, composed 
 of approximately forty local packing associations. The local associa- 
 tions are also organized on the cooperative principles. The local 
 plants grade and pack the nuts of their members in accordance with 
 the standard agreed upon by the central association. The central 
 association, by a rigid inspection, maintains the standards set and 
 performs its prime function of selling the crop. The walnut growers, 
 affiliated as above noted, thus receive the actual selling price of their 
 nuts minus the bare cost of grading, packing, and selling the nuts. 
 
Bulletin 332] WALNUT CULTURE IN CALIFORNIA 217 
 
 The walnut growers who do not belong to the cooperative associa- 
 tions usually sell their crops to the various independent packing firms, 
 who later grade and pack the nuts according to their own standards. 
 
 INCOME TO BE DERIVED FROM CALIFORNIA WALNUTS 
 
 In order to assist the beginner in considering the probable profits 
 to be derived from growing walnuts the following table has been 
 prepared. 
 
 The average yield for the state varies from year to year. Numer- 
 ous statistical publications indicate that a ten-year average yield for 
 bearing orchards is approximately 800 pounds per acre. It follows, 
 therefore, if an orchard is picked at random the chances are even 
 that the average yield for ten years is 800 pounds or less. This figure 
 has been used as a conservative estimate for business purposes in the 
 calculations below. 
 
 Goodspeed 35 found from a survey of nearly a thousand groves that 
 the cost of operation of a bearing grove was approximately $50.00 
 per acre under conditions similar to those set forth in the following 
 table, exclusive of depreciation. This figure has been increased 
 slightly from the above mentioned calculations in order to cover depre- 
 ciation and, in the especially heavy producing groves, to also cover 
 the extra cost of harvesting big crops. 
 
 Hunt 30 writes that, "A competent farmer should expect, and no 
 one should undertake to farm unless he may reasonably expect, to 
 produce 50 per cent more than the average. On this basis, the gross 
 income per annum may be estimated at 25 per cent of the capital 
 invested. This does not mean that every legitimate farm enterprise 
 will, or should bring in just 25 per cent of the capital invested. This 
 statement is only meant to give one a 'yard stick' with which to 
 measure any definite farming enterprise." 
 
 The average annual gross income from walnuts, as shown by the 
 preceding table, amounts to approximately 19 per cent of the capital 
 invested. This does not necessarily mean that the table indicates 
 an inflated capitalization of the industry, because this return has 
 attracted adequate capital to the walnut industry in competition with 
 general farming, owing to the facts that walnuts have required less 
 investment in farm machinery than many other crops; the trees are 
 long-lived, and therefore there is a smaller annual depreciation than 
 
 35 "The California Walnut," published by California Walnut Growers' Asso- 
 ciation, 1919, p. 20. 
 
 so ' ' Suggestions to the Settler in California, " T. F. Hunt, Univ. of Calif. 
 Experiment Station Circ. No. 210, 1919, p. 4. 
 
218 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 with many fruit crops and animal industries; walnuts are less perish- 
 able during the harvesting, packing, and marketing operations than 
 many crops ; and the annual prices of walnuts received by the growers 
 have gradually increased during the past twelve years, without any 
 great speculative fluctuations from year to year. 
 
 Estimate of the Average Returns which may be Expected from 
 California Walnut Groves 
 
 Yield per acre. 
 
 Safe estimate] 
 for business " 
 purposes 
 
 800 lbs. 
 
 (approximate 
 average in California) 
 $700.00 
 
 130.98 
 
 Income which 
 competent 
 ggTmen may hope 
 to obtain 
 
 1200 lbs. 
 
 Possible, 
 but 
 extra- 
 ordinary 
 
 2000 lbs. 
 
 Valuation per acre $700.00 $1000.00 $1700.00 
 
 Gross income per acre 1 130.96 196.44 327.40 
 
 Annual cost of operation 
 
 per acre 2 $55.00 $60.00 $70.00 
 
 Annual cost of packing and 
 
 marketing, per acre 16.00 24.00 40.00 
 
 Total charge per acre against 
 
 crop $ 71.00 $ 84.00 $110.00 
 
 Net income per acre 3 $59.96 $112.44 $217.40 
 
 Interest at 4% on valuation 4 28.00 40.00 68.00 
 
 Profit per acre 5 ..., $31.96 $72.44 $149.40 
 
 (Above what might have been 
 realized, with the capital in- 
 vested in safe securities and the 
 owner working out for wages). 
 
 1 Based on selling price of No. 1 nuts for ten years, 1907-1918 (16.37 cents). 
 All nuts would not be No. 1, therefore, the above returns are slightly exaggerated. 
 
 2 Includes irrigation, pruning, cultivation, harvesting, depreciation and taxes. 
 
 3 Gross returns minus all expenses. 
 
 4 The rate of 4 per cent is used here to charge against the grove as the return 
 which might have been made had the owner invested in securities rather than a 
 walnut grove. This rate of interest is in harmony with investments made with 
 a. minimum of risk and a minimum of skill and effort on the part of the investor. 
 
 5 The gross returns minus all expenses and 4 per cent of the valuation of the 
 property.