CALIFORNIA AGRICULTURAL EXTENSION SERVICE CIRCULAR 7 DECEMBER, 1926 Suggestions on Grapefruit Culture in Imperial Valley RAYMOND ELLIS PUBLISHED BY THE COLLEGE OF AGRICULTURE UNIVERSITY OF CALIFORNIA Cooperative Extension work in Agriculture and Home Economics, College of Agriculture, University of California, and United States Department of Agriculture cooperating. Dis- tributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. B. H. Crocheron, Director, California Agricultural Extension Service. UNIVERSITY OF CALIFORNIA PRINTING OFFICE BERKELEY, CALIFORNIA 1926 Digitized by the Internet Archive in 2011 with funding from University of California, Davis Libraries http://www.archive.org/details/suggestionsongra07elli SUGGESTIONS ON GRAPEFRUIT CULTURE IN IMPERIAL VALLEY EAYMOND ELLISi INTRODUCTION Present Status of the Industry. — The growing of grapefruit in Imperial Valley is an industry which is in the purely developmental stage at the present time, but which has a bright future in so far as the production of good quantities of desirable fruit is concerned. The acreage involved is increasing each year, most of the development having taken place since 1920. At the present time there are approxi- mately 5100 acres planted, with about 1500 acres bearing. Of the bearing acreage only about 200 acres have reached maturity. Growers should receive some returns from their young groves about four years after planting and the production will normally increase until the trees reach full bearing, which is at about twelve years of age. Marketing Situation.— To date very little Imperial Valley grape- fruit has been shipped outside of California, the larger cities of this state absorbing a large percentage of the production. The time is fast approaching, however, when new markets will have to be developed and the people educated to the high quality of the desert grown fruit. This campaign of education can best be carried on by actually placing the fruit in new markets and in that way creating a demand for it. There is no reason to believe but that, with high-quality fruit, raised on medium-priced land, with cheap water, low fertilizer costs, and practically no expense for insect pest and disease control — the growers of Imperial Valley can compete with any other citrus section, especially in the markets west of the Mississippi River. SOILS FOR GRAPEFRUIT Selection of Land. — The selection of a suitable piece of land is one of the first and most important problems which the prospective grower is called upon to face. Although citrus fruits will do well on a fairly wide range of soil types, there are certain ideals toward which it is well to work, as well as conditions to be avoided. The ideal soil is a sandy loam, reasonably free from alkali, having good underground drainage and containing a good supply of plant foods. The very heavy soil types which contain a high percentage of injurious salts should be avoided. 1 Assistant in Agricultural Extension. 2 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [ClRO. 7 Land which has grown alfalfa for three or more years is desirable, especially from the standpoint of soil fertility. A good stand of alfalfa is also an indication of low alkali content, and shows as well the possibility of good root penetration and distribution. Soil Types. — The Holtville series of soils^ is the best suited to grapefruit culture, of those found in Imperial Valley. This series is made up of a medium to heavy surface soil underlain at varying depths by a sandy subsoil. This last feature is desirable from the standpoint of efficient drainage. The Meloland series is also suitable, being composed of a light surface soil, underlain by a stratum of heavier materials. The presence of this heavy layer sometimes causes trouble, especially where there is a tendency to over-irrigate. The Rositas series is also used considerably and is suitable, although not found in as large bodies as the two first mentioned. This series is of lighter texture and requires the addition of much organic matter for best results. There are numerous other minor soil types and phases which are suitable, but the three mentioned are the ones of major importance. The Imperial series is, generally speaking, not so well suited and should be avoided. This series is made up of solid columns of heavy soil, varying from a heavy clay loam to a very heavy clay and gener- ally contains a considerable amount of objectionable salts. Precautions in Handling Imperial Valley Soils. — Citrus growers should use great care in handling any of the Valley soils, especially the heavier types which contain much silt. If cultivated too wet or too dry a cloddy condition will result, and if irrigated too fast proper penetration of moisture is not secured. Over-irrigation and water- logging must be watched very closely on those soil types which are underlain by strata of heavier materials. The prospective grower should never think of planting trees until a study has been made of the various underlying strata of his soil ; observation made on rapidity and depth of water penetration; and whether or not there is any indi- cation of a rising water table. This investigation can be made very easily with a soil auger. Alkali. — Practically every tract of land in Imperial Valley con- tains considerable white alkali or other salts, which if allowed to 2 Soil surveys describing soils in the Imperial Valley, and containing maps showing their occurrence can be obtained, by request, from Division of Soil Technology, University of California, Berkeley, California. Surveys are available for the Brawley Area, the El Centre Area, and the Palo Verde Area. Grapefruit is grown in Palo Verde Valley, although that district is not discussed in this circular. 1926] SUGGESTIONS ON GRAPE FRUIT CULTURE IN IMPERIAL VALLEY 3 accumulate around the roots of the trees, will cause trouble. The danger point of concentration has not been determined, as it depends on the soil type and the nature of the salt mixture. SELECTION OF STOCK Variety. — The Marsh seedless grapefruit is the most popular variety because of a market demand for a seedless fruit. It develops a high sugar-acid ratio in this region, earlier than in the cooler dis- tricts, and for that reason has developed a special reputation in Pacific Coast markets as a fruit of high quality in early season. Type of Tree. — The prospective grower should exercise great care in the selection of his young trees, in order to insure, if possible, a uniform grove, with each tree producing a good crop of high-quality fruit. An investigation of the source of the buds used is advisable, and is a point which should not be overlooked. These buds should be inserted on good thrifty seedlings. All factors being considered, the sour orange seedling is the most satisfactory, with the sweet orange and pomelo root also iairly good. All trees should be budded high, preferably six to eight inches above the ground, in order to preclude any possibility of disease which might develop from contact between the soil and the grapefruit scion. Quarantine Regulations. — Inasmuch as Imperial Valley is free from all scale insects, except the unimportant cottony cushion scale, it is to be hoped that all growers will take every precaution to prevent the introduction and spread of these pests. Before importing any trees, it is advisable to get in touch with the County Horticultural Commissioner and get the latest quarantine regulations. These regu- lations should be obeyed to the letter if trouble is to be avoided and the citrus industry of the Valley kept on a permanent basis. In case any insect pests are found in Valley groves, they should be eradicated at once. PLANTING Date of Planting. — Planting time in Imperial Valley corresponds very closely wdth that of other citrus districts of California, except that the high summer temperatures make summer planting impossible. The best planting date is March 15 to May 1, inclusive. Fall planting has been found not satisfactory. Preparation of Soil. — Land which is to be planted to citrus fruits ought to be thoroughly plowed during the fall or winter previous to planting. This is especially true of old alfalfa land, as it gives the material which is plowed under a chance to decompose before planting 4 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [CiRC. 7 time. After plowing, the land can be harrowed or disced and floated to proper grade for irrigation. High or low spots must be eliminated before planting as it is almost impossible to do satisfactory retouch- ing after the grove has been planted. Laying OtU the Grove. — Apparently the trees should be set at least twenty-four feet apart each way, in order to insure ample work- ing space when they are grown. In laying out the tract for planting, a planting wire with markers soldered on it is very useful. The markers are placed on the wire at whatever distance the trees are to be set. This wire is stretched across the field and a stake set at each marker where the trees will later be planted. The laying out and digging of the holes should be done at least two weeks before planting. This gives the soil around the holes a chance to become well aerated. Holes are dug at each one of the stakes, with the center of the hole at approximately the position of the stake. Each man who is digging carries with him an extra supply of pegs as well as a small planting board, about four feet long, with a notch at each end and one in the center. The center notch is placed over the stake which has previously been set and then pegs are driven in the two end notches. The board and center stake are then removed and the hole dug. Holes should be about two feet in diameter and about the same depth. Setting the Trees. — When trees arrive from the nursery it is imperative that they either be planted, or placed where they can be supplied with water. Loss of moisture takes place very rapidly, especially when the wind is blowing, and a great deal of damage may be done if the trees are not cared for immediately. When planting is going on, the same planting board which was used at digging time is again carried. The board is placed over the two stakes, and the tree set in the hole with its trunk in the center notch of the planting board. This insures a straight line of trees. If the hole is too deep it should be filled in with moist surface soil and not with grain, straw, fertilizer, or any other material which might damage the young tree roots. The tree should be set about two inches higher than it was in the nursery so that settling will be allowed for. Where balled trees are used it is advisable to cut the sacking at the top and let it fall back into the hole and the ball broken slightly. With bare rooted trees, all broken or deformed roots should be removed before setting. Planters ought to have a stream of water following them closely at all times and after each tree is set and the soil thoroughly tamped around it, the water should be turned in and the roots and soil around 1926] SUGGESTIONS ON GRAPE FRUIT CULTURE IN IMPERIAL VALLEY 5 them given a good soaking. Too much emphasis cannot be placed on proper firming of the soil around the tree in order to secure a proper contact between the roots and soil. This firming should be done before the water reaches the tree. Balled vs. Bare Boot Trees. — Generally speaking balled trees are the more satisfactory under Valley conditions. Drying out of the root system is not so apt to take place and the hazards of planting are not so great, providing the operations are properly carried out. There are some things to be said in favor of bare rooted trees, however. In the first place it allows for an inspection of the root system and the removal of undesirable roots, as well as doing away with the payment of freight charges on large quantities of soil. Provided the grower, himself, is to superintend the planting operations, and with weather conditions just right, then bare rooted trees may be used. PROTECTION AGAINST UNFAVORABLE CLIMATIC CONDITIONS Wind and Windbreaks. — The prevailing winds in Imperial Valley come from the north and west, reaching their greatest intensity during February, March and April, and doing most of their damage during that time. Every year growers lose heavily through partial defolia- tion of their trees, as well as scarring of the fruit, and the resultant lowering of the grade. The actual damage in dollars and cents is hard to estimate, but it has been officially stated that, of the fruit entering the packing house of the Imperial Valley Citrus Association during the 1924-25 season, 25 per cent was cull fruit, 35 per cent second grade, and the remainder first grade. According to the house manager, 90 per cent of the cull and second grade fruit was so placed because of wind injury. Add to this the injury done to the trees and the loss due to fruit being blown off and one can readily see the need for adequate protection. The best means of protection is an efficient windbreak of some variety of evergreen tree. There are several varieties of trees which do well in the Valley and are also suitable for windbreak purposes. Among these is the athel {Tamarix articulata) , a fast growing ever- green, well suited to desert conditions (see fig. 1). It is easily propa- gated from cuttings and when well cared for makes a dense growth very quickly, even though somewhat low for an ideal windbreak. Some of the varieties of eucalyptus are also very good, among these being the gray gum {Eiicalypius tereticornis) , red gum (Eucalyptus rostrata), and blue gum (Eucalyptus globulus). A very effective and desirable windbreak is one of eucalyptus interset with athel. CALIFORNIA AGRICULTURAL EXTENSION SERVICE [CiRC. 7 Regardless of the variety of tree used, growers should cut to a minimum the competition between the windbreak and the orchard trees. This can best be accomplished by proper fertilization and irrigation of the windbreak, as well as a proper system of root prun- ing. Subsoiling deeply between the windbreak and the first row of orchard trees is an effective method of root pruning. This operation should be carried out at least twice each year, with the cut being made at the same place each time. Fig. 1.— Typical athel windbreak. Providing the grower is desirous of protecting his young trees, it is best to plant the windbreak at the same time as the grove is set out, or even before, depending on the growing habit of the trees selected. Windbreak trees should be set approximately six feet apart and then as they overlap in later years, part of them may be removed. Plenty of space must be left between the orchard trees and the windbreak, so that turning with cultivating tools and root cutting will be facilitated and root competition reduced to a minimum. Sunburn. — The protection of the trunks of young trees from the sun is one of the first considerations after planting. The young trees, for the first two or three years, have no natural protection on the trunks in the way of foliage, consequently they must be taken care of artificially. This protection may be accomplished in several different ways. Yucca and waxed paper protectors, placed around the trunks, are very effective, but are not used very largely because they create a harbor for insects which often damage the young trees. Whitewash is also good and is to be recommended under Valley conditions. It 1926] SUGGESTIONS ON GRAPE FRUIT CULTURE IN IMPERIAL VALLEY 7 scales off to some extent, but by getting a good mixture and making two or three applications during the summer, very satisfactory results can be obtained. Several mixtures of whitewash may be used. Cold water paint, a white powder much like kalsomine, is very good because of its tendency to stick to the tree trunks. This powder should be mixed with water until a thick, creamy mixture is obtained. A formula made up of ten pounds of quicklime and three pounds of sulfur has also proved satisfactory. The quicklime should be slaked with water and the sulfur added while the heat is being given off. The mixture must be cool before being applied to the tree. The maintenance of a good coat of tree whitewash throughout the first two or three years is a task, but is undoubtedly worth while, not only from the standpoint of tree protection, but also because it fur- nishes opportunity for better acqaintance with individual trees. Frost. — The hazard of freezing temperatures is considerable in the Valley, especially with reference to the young trees. Fruit is also damaged at times and considerable loss sustained by some growers. During the winter of 1924-25 this was especially true, as a good part of the fruit which remained on the trees at the time of the low temperatures was lost. Although young trees are often damaged considerably by cold weather, the mature trees, providing they are in a healthy condition, are very seldom affected to any great extent. Sometimes a few leaves and small branches are lost, but the recovery is rapid with the advent of warm weather. The cold waves which visit Imperial Valley correspond very closely to those in other parts of southern California, both as to duration and intensity. Growers should be concerned largely with bringing their groves through the first three years as that is the critical period in so far as frost damage is concerned. There are several rules to follow if this damage is to be reduced to a minimum. The trees must be kept healthy through proper moisture supply and soil fertility, as well as free from insect pests and diseases. Providing the trees are in good physical condition, the problem then resolves itself into one of protecting the small tree trunks with some such insulating material as cornstalks, tules, or arrow weed (see fig. 2). This material, a bundle about ten inches in diameter, should be set in place during the latter part of November and left on until about the first of March. It is imperative that the bundle be tied snugly around the tree trunk, once near the ground, again half- way up the trunk, and a third time just below the head of the tree. 8 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [CiRC. 7 The wrapping material is allowed to go up through the head of the tree in order to protect the main framework branches, but no attempt should be made to pull the foliage inside the bundle. The tree and its protecting material, during the first winter at least, should be staked to prevent blowing over by the wind. Ordinary redwood grape stakes are very satisfactory for this purpose. The stakes are driven into the ground, preferably on the west side, after the insulating material has been set in place. The tree and bundle need to be tied to the stake in only one place, that being as high up on the tree as possible. Fig. 2. — Showing proper method of protecting young tree trunks from frost damage. Note stake to prevent blowing over. The initial cost to growers for this system of protection, including stakes, wrapping material and labor, will be approximately ten cents per tree. The exact cost will depend largely on the kind of stakes used and the speed with which the work is done. It remains to be seen whether or not Imperial Valley growers will install orchard heating systems when these young groves come into bearing. A careful study of the economics of the situation should be made showing a comparison of the annual losses sustained, with the cost of installing and maintaining an adequate heating system.^ 3 Figures on costs of orchard heating have been given in California Agr. Exp. Sta. Bui. 398, Orchard Heating in California, by Warren E. Schoonover and Eobert W. Hodgson, in cooperation with Floyd D. Young of the United States Weather Bureau. 1926] SUGGESTIONS ON GRAPE FRUIT CULTURE IN IMPERIAL VALLEY IRRIGATION The proper irrigation of a citrus grove is an important operation, especially in a region where the average annual rainfall is about three inches and the evaporation very high. Irrigation does not mean the application of great quantities of water at regular stated intervals, but is rather the judicious wetting of the root zone at such times as the tree needs it. This does not mean that it is either necessary or desirable to have the soil kept evenly wet. On the other hand, it seems that the trees do better if the soil moisture fluctuates from very wet to very Fig. 3. — Showing furrow irrigation, using only two inside furrows. near the wilting point. Trees should not be allowed to suffer for water, but soil aeration is facilitated as the moisture content grows less, and as a consequence root growth is benefited and the tree invigorated, providing the soil does not become too dry. Very early in the life-history of the grove, the owner should make a study of his soil with reference to water penetration and holding capacity. On this study will be based the frequency and amount of water to be applied, length of run, size of head and to some extent the method of application. This study can be made by cutting trenches across the irrigation furrows and also by the use of a soil auger. The system of irrigation to be used will depend to some extent on the soil type as well as on the age of the grove. With young trees it is not necessary to wet all of the soil between the tree rows at every irrigation. Two furrows, one on each side of the row, may be used for four or five irrigations (see fig. 3). The entire area should be thoroughly wet two or three times during the year. A combination 10 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [CiRC. 7 of furrow and flood irrigation is especially desirable where there is any amount of objectionable salts or alkali present. Flooding is not so desirable as a general practice, but can be used to good advantage to redistribute any of the salts which might be present. Flooding can be done at almost any time of the year, but preferably in the winter. Fig. 4. — Showing after effects on soil of flood irrigation. Note center border. It is best done by throwing up a border midway between the tree rows and running the water between the borders and directly down the tree row (see fig. 4). Groves planted on the sandier soil types are best not flood irri- gated, as these soils have a tendency to take too much water. This not only causes a waste of water, but also may cause trouble from a 1926] SUGGESTIONS ON GRAPE FRUIT CULTURE IN IMPERIAL VALLEY 11 local water table, especially if there is a heavy subsoil present. The sandier soils, as a general rule, do not contain any great amount of alkali, so that flooding is not necessary from the standpoint of redistribution of salts. CULTIVATION Cultivation to conserve soil moisture is important only in so far as it controls weeds or eliminates large cracks in the soil. If culti- vation is done at the proper time, soil aeration is helped to some extent. It is not necessary to cultivate the grove after each irrigation. On the other hand, it seems desirable that, at least three or four times each year, the grove be left uncultivated between irrigations, so that the soil will dry out and crack, thus permitting the entrance of fresh air into the soil as well as assisting the water penetration at the next irrigation. This practice is to be especially recommended on the heavy soil types. Practically all of the Imperial Valley soils contain large amounts of such very fine materials as silt and clay, consequently must be handled with great care. If plowed when either too wet or too dry, huge clods will be turned up and if disced or shallow-cultivated when too wet, an impervious plowpan may be formed. The proper time at which to cultivate is an individual problem and must be studied by each grower. It is .not necessary to take so many precautions with the sandier soil types. MAINTENANCE OF SOIL FERTILITY The Imperial Valley citrus grower should adopt and follow an adequate fertilizer program from the very first if best results are to be obtained. Nitrogen is the element which is most likely to be deficient in the Valley soils, and any program adopted should provide especially for the addition of this element. Cover Crops. — During the first three or four years, while there is considerable space between the trees, soil fertility can best be main- tained by means of leguminous cover crops. These crops may be grown either in summer or winter, or both if the land is none too fertile. The grower has a number of satisfactory legumes from which to choose. It is desirable that one be selected which is deep rooting, especially on the heavier soils. Production of a large tonnage of green tops is also desirable. Among the winter crops which are satisfactory, are the garden pea, sour clover {Melilotus indica), and berseem or Egyptian clover. 12 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [ClRC. 7 The first named is very good, as it not only serves as a cover crop, but also promises some financial return, providing it is planted early in the fall and a normal year encountered (see fig. 5). Some of the summer legumes which are satisfactory are sesbania (wild hemp), Brabham and Iron cowpeas, and several varieties of soybeans. All of these produce good tonnages of green tops and root deeply. Where a summer crop is grown the grower should watch his soil moisture conditions very closely, so that no competition for water takes place between the trees and the cover crop. This holds true for a winter crop, also, but to a lesser extent. Fig. 5. — Winter cover crop of garden peas in young grapefruit grove. Other Fertilizers. — When the trees have grown to such a size as to cut down materially the available growing space for cover crops, then other fertilizers must be used. Organic matter is always necessary, so that manure, bean straw or alfalfa hay should be used. The amount to be applied will depend on the material and its nitrogen content. Sufficient material should be applied annually to furnish each tree with one to one and a half pounds of available nitrogen. The application of these bulky organics is best made in the early fall, preferably in October. In order to supplement the fall application of organic matter, a quickly available nitrogenous commercial fer- tilizer should be used in the early spring. An additional pound of available nitrogen per tree should be added in this way. The above outlined program should care for the ordinary grove and keep its production at a good level, providing other conditions are normal.* 4 Further information bearing on special conditions may be found in California Agr. Exp. Sta. Cir. 283, Fertilizing Citrus Trees in California, by Eobert W. Hodgson. 1926] SUGGESTIONS ON GRAPE FRUIT CULTURE IN IMPERIAL VALLEY 13 PEST CONTROL Cottony Cushion Scale. — The pest control problem among citrus growers of Imperial Valley is as yet comparatively simple. None of the scale insects so common in other citrus districts have yet been introduced, except the cottony cushion scale. There are several infes- tations of this insect, but it can be controlled by the use of the Australian ladybird, which feeds upon it. These ladybirds may be secured on application to the County Horticultural Commissioner. Fire Ant. — The fire ant {Solenopsis gemi- nata) is the most important of the insects at- tacking citrus trees in this region. This is a small red ant which appears with the warm weather in late spring or early summer, and works only on the young trees. The ants make their nests among the roots of the small trees, coming out onto the limbs and trunks to feed on any fresh sap which might break out over the tree. They not only feed on the sap, but eventually start to work on the tender bark and if left un- molested for a few days will completely girdle a young tree (see fig. 6). Certain control measures can be recom- mended which, if followed, will materially lessen the danger from these insects. Tree whitewash is preferable to protectors, because it does not afford a harbor behind which the ants can work. The application of two or three coats of whitewash also gives the grower the occasion to inspect each individual tree for evidences of any damage. When an ant nest is found, the application of two or three teaspoonfuls of calcium cyanide dust or flakes around the base of the tree will destroy a large percentage of the ants. This material should be placed at least two inches away from the tree trunk and on the surface of Fig. 6. — Damage to young grapefruit shoot by fire ant. 14 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [CiRC. 7 the ground. Infested trees should be marked, and at the next irri- gation, which should not be sooner than twenty-four hours after the application of cyanide, the irrigator should cut the water in around these trees and drown out any of the remaining ants. Tree tanglefoot has been used to good advantage by some growers, but with the advent of cool nights the material has a tendency to harden and lose its effectiveness. Tlirips. — There are several species of thrips found in Imperial Valley, chief among them being the grain thrips. This insect is often found on the citrus trees, but is of little economic importance to the growers because the damage done by it is negligible. However, some growers are desirous of trying control measures at times, in which case a 2 per cent lime-sulfur solution may be used experimentally. This solution should be applied as a spray at blooming time. DISEASES None of the diseases common to citrus trees are of any importance in Imperial Valley, except possibly brown rot gummosis {Phythiacistis citrophtho7^a) . Even this is of little importance under the existing weather conditions. It develops best in a cooler, more humid environ- ment. However, it is found occasionally, but can be cured rather easily by cutting out the diseased portion and applying some dis- infectant such as Bordeaux paste or a good whitewash. This disease always appears on the lower part of the trunk and is characterized by the presence of a rather dark colored gum. Under no circum- stances should growers confuse this disease with the light colored gum often found on the trunk and limbs of young trees. This latter is not a disease, but is probably due to improper soil moisture conditions, and should cause no worry except that ants may be attracted by the fresh sap. PRUNING General Pruning. — The pruning of healthy, growing trees is a very minor operation. After being properly headed when young, it should not be necessary to touch them for at least four years. After the trees come into bearing, there will be some pruning to do each year. Dead wood and interfering branches are best removed. If the tree is very dense, a small amount of leaf surface should be removed, in order to admit more air and sunlight and thus promote the growth of more inside fruit. The removal of any leaf surface should be done in the winter time, when the trees are as nearly dormant as possible. Growers 1926] SUGGESTIONS ON GRAPE FRUIT CULTURE IN IMPERIAL VALLEY 15 should not remove too much growth from the south side of any tree, as sunburning of the trunk or main framework branches might result. Water sprouts coming on the trunk and main framework branches ought to be removed when small, so that the resultant wounds will be of minor importance and will heal quickly. Fig. 7 Fig. 8 Fig. 7. — Young grapefruit tree before pruning out dead wood and suckers, after being frozen. Fig. 8. — Same as figure 7, after pruning. Special Pruning for Frost Injured Trees. — Occasionally trees are severely injured by low temperatures and require special treatment during the following year. This applies to young trees, especially, as none of the older ones have as yet been injured to any extent by cold weather. This treatment should consist only of proper irrigation and cultivation for two or three months after the removal of the protecting materials. Care must be taken not to over-irrigate, as the new growth should be as healthy as possible. In those cases where all the foliage has been frozen but the trunk and main framework branches unhurt, it is best to force growth as rapidly as possible. No pruning should be done until June or later. By that time all of the frosted wood will have died back and can be removed (see figs. 7 and 8). Any water sprouts on the trunk may also be removed. If, in the judgment of the 16 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [CiRC. 7 grower, the removal oi all the sprouts or suckers will be too great a reduction of leaf surface for the good of the tree, some of them may be left on until the following winter. Some of them may also be cut half way through and bent over so as to reduce the rapidity of sap flow and then entirely removed the following fall. This practice is known as lopping and works to advantage in many cases. As soon as the protecting materials have been removed in the spring, any exposed trunl^s and main branches should be whitewashed to prevent sun- burning. Oftentimes trees, especially those in their first year, are more severely frozen, necessitating either removal or the building up from a new shoot. There seems to be some advantage in this latter method-, as the root system is already well established and growing. There will be some trees, however, which are so severely frozen that the new growth will be weak and spindling, in which case replanting is advis- able. It is not practical to try to save and rebud trees frozen below the bud union. Kebuilding a frosted tree from a shoot which has arisen from the trunk, above the bud union, can be accomplished by careful handling and considerable work. All new shoots which come out should be allowed to grow until about April, when the most vigorous one is selected and tied up loosely, either to a stake or to the old stump. This is done in order to train the new tree trunk in an upright habit of growth. About a quarter of the new shoots may be removed in June and the remainder lopped over until the following winter, when they can be removed. It is advisable that an extra shoot besides the one selected be left, in case the latter should be broken off. This extra branch may also be removed during the following winter. If possible, the new tree trunk should be brought out on the west side of the old one, so as to lessen the possibility of breaking off by the wind. When the new tree trunk has attained a height of about three feet, it should then be headed back to the desired height. When it has become strong enough to support itself, then the old stump should be removed and the wound covered with grafting wax. Subsequent treatment should be the same as for any other young tree. INTERCROPPING WITH CASH CROPS Inasmuch as there is considerable unused land between the rows of young grapefruit trees, the grower can sometimes make a part of his expenses by growing some cash crop between the rows. The trees will not be harmed in any way, providing the grower always keeps 1926] SUGGESTIONS ON GRAPE FRUIT CULTURE IN IMPERIAL VALLEY 17 in mind the fact that the grapefruit is the chief crop under consider- ation and is guided accordingly, especially in his fertilization and irrigation programs. Garden Peas. — This crop, which was mentioned briefly under winter cover crops, is a very satisfactory and desirable intercrop. Planted as soon as the weather breaks in September, it will, under normal conditions, produce a crop of peas during the early winter. These peas are generally sold for a fair price at that time of the year, thus returning to the grower some of his expenses, as well as building .up the fertility- of the soil. Fig. 9. — Alfalfa intercrop. Showing also proper method of irrigating trees separately from intercrop. Alfalfa. — Some growers have used alfalfa to advantage as an inter- crop (see fig. 9). The crop should be planted in October, before the grove is to be set out. About December the grower should plow strips through the alfalfa for his tree rows. These strips ought to be at least five to six feet wide. The trees are then set in the bare strips during the following spring. The alfalfa may be safely left in the grove for at least three years, provided the strips are widened each year, so as to preclude any possibility of competition between the intercrop and the trees. Miscellaneous Cash Crops. — There are a number of non-leguminous intercrops which may be used, provided competition for water and plant food is cut to a minimum. Some of these annual crops are cantaloupes, lettuce, watermelons, tomatoes, and corn. In the case of corn the stalks are later used in frost protection. All of these crops take much plant food from the soil, a point to be borne in mind when determining upon the cash crop. They also are very different from the trees in their fertilizer, soil moisture, and other cultural require- ments. However, they do offer some promise of a cash return each year until the trees come into bearing, and will not injure the trees if proper care is taken. 18 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [CiRC. 7 CONCLUSION The future of the grapefruit industry in Imperial Valley will depend to a large extent on the growers themselves. They should not expect the high prices to continue which have prevailed during the past five years, especially after the new acreage in Texas, Florida, and Arizona comes into bearing. However, there is every reason to believe that the grower may expect a fair profit on his investment, providing the trees are kept at a high state of production by means of proper orchard practices and the cost of operation kept at a minimum by means of good business methods. The growers must also cooperate with each other in advertising and selling their product if they are to secure the best results.