CALIFORNIA 
 AGRICULTURAL EXTENSION SERVICE 
 
 CIRCULAR 60 
 
 March 1932 
 
 The Head-Lettuce Industry 
 of California 
 
 H. A. JONES and A. A. TAVERNETTI 
 
 Cooperative Extension work in Agriculture and Home Economics, College of Agriculture, 
 University of California, and United States Department of Agriculture cooperating. Distributed 
 in furtherance of the Acts of Congress of May 8 and June 30, 1914. B. H. Crocheron, Director, 
 California Agricultural Extension Service. 
 
 THE COLLEGE OF AGRICULTURE 
 
 UNIVERSITY OF CALIFORNIA 
 
 BERKELEY, CALIFORNIA 
 
Digitized by the Internet Archive 
 
 in 2011 with funding from 
 
 University of California, Davis Libraries 
 
 http://www.archive.org/details/headlettuceindus60jone 
 
THE HEAD-LETTUCE INDUSTRY OF CALIFORNIA 
 
 H. A. JONESi and A. A. TAVERNETTI2 
 
 FOREWORD 
 
 Within the past 12 years the production and consumption of 
 lettuce in the United States have been greatly increased, largely 
 through the education of the public regarding the health-giving prop- 
 erties of that food." Figure 1 shows the carlot shipments of lettuce 
 
 i 
 
 
 I 
 
 'ec" 'PS 'P4 -ps 'ee 'er 
 
 '2S -eg /930 
 
 Fig. 1. — Carlot shipments of lettuce for the United States for the years 
 1918 to 1930, Shaded j)ortions are California shipments. 
 
 in the United States and in California since 1917. Much of the lettuce 
 produced near the large consuming centers is now being hauled to 
 market by truck and therefore does not appear in these carlot totals. 
 In 1930 over 67 per cent of all carlot movements of lettuce in the 
 United States originated in California. During the same year this 
 state moved as many cars of lettuce as the entire country did in 1925 
 and over five times as much as the entire country did in 1918. 
 
 1 Professor of Truck Crops and Olericulturist in the Experiment Station. 
 
 2 Specialist in Agricultural Extension. 
 
 3 For a detailed discussion of the economic aspects of the lettuce industry 
 see: Wellman, H. E. Lettuce: series on California crops and prices. California 
 Agr. Ext. Ser. Cir. 5, 1926. 
 
California Agricultural Extension Service [Cir- 60 
 
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1932] 
 
 The Head-Lettuce Industry of California 
 
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California Agricultural Extension Service [Cir. 60 
 
 PRODUCTION AREAS IN THE UNITED STATES 
 
 Production areas of more or less importance are scattered through- 
 out the entire country. The New York variety is raised mainly in 
 the irrigated regions of the West, the most extensive areas being 
 located in Arizona, California, Colorado, Idaho, and Washington. At 
 present certain strains of New York are being grown successfully in 
 the East, but they are not yet cultivated there extensively. The variety 
 Big Boston is grown in the Middle West, East, and South, particularly 
 in New York, North Carolina, South Carolina, and Florida. 
 
 Table 1 gives the carlot shipments of lettuce by states for the year 
 1930. Although the shipping season of each locality varies slightly 
 from year to year with seasonal conditions, the table, nevertheless, 
 gives the approximate time when lettuce may be expected to move 
 from the different districts. 
 
 PRODUCTION AREAS IN CALIFORNIA 
 
 The two main lettuce-producing areas of California are the Im- 
 perial Valley and the Salinas-Watsonville district, comprising the 
 lower Salinas and Pajaro valleys. A number of other districts, how- 
 ever, are located along the coast and in the interior valleys. Their 
 relative importance is shown in table 2, which gives the carlot 
 shipments of lettuce by counties for the different months. 
 
 Shipping Seasons for California Lettuce. — Lettuce moves from 
 California in quantity all the year around. In 1930 the lightest ship- 
 ments were in June, with a total of 1499 cars. From the Imperial 
 Valley the lettuce movement is mainly during December to March ; 
 in the Salinas Valley, from April to November, with the spring peak 
 coming in May and the fall peak in October. 
 
 Distribution of California Lettuce. — California lettuce is widely 
 distributed throughout the United States and Canada during the entire 
 year. Most of it is shipped in carlots, but some is moved in mixed 
 cars. A considerable quantity, in addition, is moved to nearby markets 
 by truck, without ice in the containers. 
 
1932] The IIead-Lettuce Industry of California 
 
 CLIMATIC AND SOIL REQUIREMENTS 
 
 Lettuce of high quality can be produced only where the tempera- 
 ture of the soil and air is moderately cool and uniform while the crop 
 is maturing. This requirement must be kept in mind, especially by 
 those who are attempting to mature lettuce during the summer. Fluc- 
 tuating high and low temperatures are not conducive to good growth. 
 High temperatures favor the production of seed stems, cause a bitter 
 taste in the leaves, produce loose heads, and accelerate the development 
 of lettuce diseases. During the early stages of development, lettuce 
 will tolerate a considerable amount of frost; but, if severely frosted 
 when mature or nearly mature, it is more subject to slime and there- 
 fore does not ship well. Generally, frosted lettuce needs close trimming 
 and is therefore not attractive. The maturing plants make very little 
 growth dui'ing continued frosty weather: although the heads may 
 become solid, they remain small, their leaf tips are injured, and the 
 trade considers them undesirable. 
 
 Lettuce must have an adequate supply of moisture throughout the 
 growing season. An excessive amount of water in the soil is, however, 
 not desirable ; and too much fluctuation in soil moisture may cause 
 the production of small, loose heads. 
 
 Lettuce is grown successfully on a wide variety of soil types rang- 
 ing from clay loams to sandy loams and muck, but it attains its 
 highest quality on fertile loam soils rich in organic matter. Where the 
 fall crop is subject to high temperatures during its early development 
 or where it matures during warm weather, the heavier types of soil 
 should be used, for they hold more moisture and are cooler. The 
 lighter, well-drained soils may be used to produce the crop that is 
 planted and grows during the cool season of the year. Because the 
 adobe soils cannot be worked soon after a heavy rain, a definite 
 planting schedule cannot easily be followed where rainfall is heavy 
 during the period of preparation and planting. All lettuce land should 
 be well drained and properly leveled for irrigation. 
 
California Agricultural Extension Service [Cir. 60 
 
 MAINTAINING SOIL FERTILITY 
 
 About 80 to 85 per cent of the lettuce crop is grown by large 
 operators, who lease the land for periods of one to five years. When 
 the lease expires growers often find it more profitable to lease new 
 land that has been in alfalfa or other crops for a number of years, 
 than to continue to plant on a soil that shows declining yields. 
 
 The soil problems involved in lettuce growing are chiefly those 
 of maintaining a good soil in a highly productive state. Where good 
 lettuce land is almost unlimited, as in the Imperial Valley and north- 
 central districts of California, this problem is not so difficult. In 
 the central-coast district of the Salinas-Watsonville area, ideal condi- 
 tions prevail for growing of summer lettuce but the area of land is 
 limited. Here the only possible procedure is to plant the same soils 
 to lettuce year after year. 
 
 Crop Rotation. — Although as many as five or six crops of good 
 lettuce have been grown consecutively, usually no more than two are 
 profitable without some sort of rotation, because various lettuce 
 diseases accumulate in the soil and infect succeeding crops. 
 
 In the Imperial Valley, alfalfa is commonly used in the rotation. 
 Lettuce is often planted directly on alfalfa sod, but more often canta- 
 loupes or some similar cultivated crop is grown first. As a rule it is 
 difficult to make a good lettuce seed bed and to control weeds immedi- 
 ately after alfalfa. Lettuce growers of the Imperial Valley follow 
 no one system of rotation. Sometimes an early crop of lettuce and a 
 late crop of cantaloupes are grown the same year. After being in 
 cultivated crops for three or four years, the land is, as a rule, resown 
 to alfalfa. A deep-rooted legume crop followed by a series of 
 shallow-rooted nonlegume crops makes a good rotation. 
 
 In the San Fernando Valley, lettuce is grown very commonly as an 
 intercrop among deciduous fruit and English walnut trees, as shown 
 in figure 2. It is planted in the fall when the trees are bare, so that 
 extreme shading does not occur. Spring lettuce is also grown after 
 fall crops of cauliflower, tomatoes, celery, or fall lettuce. Fall lettuce 
 often follows spring potatoes. For the fall crop, seed is sown in 
 August or September; for the spring crop, in November, December, or 
 January. In Los Angeles County, where land is high-priced, it must 
 be kept occupied with highly profitable crops. 
 
 In the Salinas-Watsonville district the growing of two or more 
 crops on the same soil in a year is now an established practice. This 
 
1932] 
 
 The Head-Lettuce Industry of California 
 
 district is very fortunate because a large number of crops can be 
 grown profitably in rotation with lettuce. It is possible to work out a 
 rotation with lettuce planted for harvesting any time of the year. 
 
 Certain crops are harvested immature, require frequent irrigation, 
 and leave the soil moist at harvest time ; examples of these are lettuce, 
 spinach, green peas, cauliflower, cabbage, broccoli, Brussels sprouts, 
 endive, carrots, and celery. These should be rotated with crops that 
 are harvested mature, that require less frequent irrigation, that leave 
 
 / 
 A'- 
 
 
 -^ ^%. 
 
 %.. 
 
 
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 Fig. 2. — Lettuce growing between English walnut trees in 
 Los Angeles County. (From Circ. 295.) 
 
 the soil dry at harvest time — such as dry beans, sugar beets, fall pota- 
 toes, onions, garlic, tomatoes, barle}^, wheat and vetch, garden pea seed, 
 and sweet pea seed. 
 
 The following crops can be grown for spring harvest and still allow 
 sufficient time to mature a crop of lettuce during the summer or fall : 
 lettuce, garden peas, carrots, spinach, sugar beets, sweet pea seed, 
 onions, garlic, green peas, vetch seed, wheat, and barley. The follow- 
 ing crops can be grown for fall harvest: lettuce, green peas, sugar 
 beets, tomatoes, potatoes, carrots, cauliflower, spinach, and celery. 
 
 Though there are a large number of crop rotation systems, the 
 individual must determine the exact procedure to meet his particular 
 needs. A few suggestions, however, may serve as a guide. One plan is 
 to alternate two crops of lettuce with one rotation crop, an arrange- 
 
10 California Agricultural Extension Service [C^ir- ^o 
 
 ment whereby lettuce can be grown on two-thirds of the available 
 acreage. Another plan now being practiced successfully by a few let- 
 tuce growers is to carry out the above rotation, but in addition to keep 
 one-fourth of the land in alfalfa for three to four years. Alfalfa, how- 
 ever, does not fit well into the general lettuce-farming plan in the 
 Salinas-Watsonville district and can be grown profitably only by those 
 who have means of marketing or using the hay. Lettuce growing in 
 conjunction with dairying and alfalfa growing is an ideal combination 
 but one which, unfortunately, is practiced to only a limited extent. 
 
 The refuse of all crops, such as straw, stalks, or unharvested plants, 
 adds organic matter and should therefore be returned to the soil. If 
 large amounts of straw or similar material are turned under, com- 
 mercial fertilizers are usually needed to offset temporary decreased 
 fertility during decomposition. 
 
 With 80 to 85 per cent of the California lettuce grown on leased 
 land, the establishment of crop rotation as a practice is not alone the 
 problem of the grower and shipper, but also that of the landowner. 
 As rentals are based mainly on the ability of the land to produce 
 marketable lettuce, landowners who wish continuously to enjoy a satis- 
 factory income from their land obviously must use farming practices 
 that will keep their soil highly productive. 
 
 A lease should not dictate just what crops are to be grown; but it 
 might be well to stipulate in the lease the number of crops of a single 
 commodity to be grown in succession on the same soil, the disposi- 
 tion of crop by-products having fertilizer value, and other similar 
 conditions of soil management. 
 
 Need for Organic Matter. — Active organic matter in the soil is 
 essential to lettuce production. This term is applied to organic mate- 
 rial which is decomposing and is capable of sustaining bacterial life. 
 The amount required varies with the soil type. Sandy and porous 
 soils usually have a very high rate of decomposition and become 
 depleted much faster than the heavy soils. If sufficient active organic 
 matter is maintained, additional fertilizing may not be required. 
 
 Organic matter in the soil may become inactive through constant 
 wetting or from cultural practices used in connection with growing a 
 specific crop. A crop rotation that allows moderate drying and airing 
 of the soil appears to stimulate decomposition of organic matter which 
 has become inactive. Organic matter lightens the heavier soils, thereby 
 improving aeration and water joenetration. It is usually supplied to 
 the soil in the form of barnyard or other types of manure or by the 
 growing of green manure crops. 
 
1932] The Head-Lettuce Industry of California 11 
 
 Manures. — Probably the best fertilizer for lettuce is barnyard or 
 other types of animal manure. If they are well pulverized, the manures 
 are usually applied and worked into the soil just before the beds are 
 listed. Fresh and coarse manure should usually be composted before 
 being- applied to the land, especially if lettuce is to be planted immedi- 
 ately. In composted manure, more of the plant food elements are in 
 an available form, there is no coarse material to interfere with plant- 
 ing and cultivation, many of the noxious weed seeds have been 
 destroyed, and there is no heating of the soil. In composting, however, 
 one should try to prevent leaching of the soluble salts and the loss of 
 ammonia by heating. Fresh or unrotted manure, if used, should be 
 plowed or disked under in time to decompose partially before the crop 
 is planted, or should be used in light applications. Decomposition of 
 the manure after it has been plowed under may be accelerated by 
 flooding the land. In tests conducted in the Imperial Valley, an appli- 
 cation of 10 tons of barnyard manure to the acre increased the total 
 yield 54 per cent, caused the lettuce to mature two to four weeks 
 earlier, and resulted in the production of larger heads, better in 
 quality, than the adjoining unmanured plots. Applications of manure 
 on land in the Salinas Valley and other districts have produced a 
 striking response. Excessive applications, however, especially in warm 
 weather, often cause the formation of loose heads. 
 
 Green Manure Crops. — Where manure cannot be obtained in suf- 
 ficient amounts to supply the needed organic matter and plant food, 
 green manure crops, alone or in conjunction with commercial ferti- 
 lizers, may be used. To grow green manure crops is better than to let 
 the fields lie idle during a part of the year. Such crops keep down the 
 weeds, add to the total organic content, and help conserve the soluble 
 mineral elements of the soil, especially in regions of heavy winter 
 rainfall. They prevent erosion, help aerate the subsoil, and increase 
 the favorable bacterial flora of the soil. They improve the texture 
 of sandy soils and to some extent increase their moisture-holding 
 capacity. 
 
 The covercrop, or the green manure crop (preferably a legume) 
 that is chosen, should be adapted to the local climatic conditions and 
 should produce a good tonnage of vegetable matter. The choice of a 
 crop will depend upon the planting time and the growing season. 
 Usually a thorough disking is given before the green manure crops are 
 plowed under. If the soil is dry, irrigation after plowing will hasten 
 decomposition. This must be fairly complete before the next crop is 
 planted ; otherwise, injurious results may follow. 
 
12 California Agricultural Extension Service [Cir- 60 
 
 In the Salinas-Watsonville district, green manure crops, such as 
 vetch or Melilotus indica, are planted in early fall after the lettuce has 
 been harvested. One must usually irrigate the land to germinate the 
 seed; thereafter, the winter rains are sufficient to mature the crop. 
 The following spring, the growth is disked and plowed under. Garden 
 peas are also used extensively for green manure purposes, the vines 
 being turned under as soon as the crop has been picked. 
 
 In the Imperial Valley, alfalfa is used rather often in the rotation. 
 Green manure crops are also employed to supply the necessary organic 
 matter. In one small test, Hubam clover appeared to offer promise as 
 a spring covercrop. When planted from March 15 to April 10, it can 
 
 Fig. 3. — Brabliam cowpeas in Imperial Valley. This crop will yield about 24 
 tons of green tops to the acre. It is resistant to the attacks of nematodes. (From 
 Cir. 295.) 
 
 be plowed under late in June. Brabham cowpeas (fig. 3) and Laredo 
 soybeans have been shown to be good summer green manure crops : 
 they produce a heavy growth and are resistant to nematode attack. 
 They are usually planted from April 15 to May 15 and require about 80 
 days to mature. Guar is another heavy-producing, summer-growing, 
 nematode-resistant legume. It is planted in June and requires about 
 100 days to mature. The green manure crop now used in Imperial 
 Valley almost to the exclusion of all others is the common legume 
 Seshania macrocarpa. In trials at the Meloland Field Station, a red- 
 stemmed species, Seshania cannabina, appears to offer equal if not 
 greater promise. Sesbania is usually broadcast at the rate of 40 to 60 
 pounds of seed per acre, between May 15 and July 15, on land pre- 
 pared flat for flood irrigation. It produces a crop that can be plowed 
 under in 40 to 60 days. 
 
1932 
 
 The Head-Lettuce Industry of California 
 
 13 
 
 The advantages of sesbania are its suitability to Imperial Valley 
 conditions, its rapidity of growth, its cheapness of production, its 
 adaptability to flood irrigation, and its rapid decay. It outgrows most 
 weeds. Most of the other summer crops, such as cowpeas, soybeans, 
 and guar, grow more slowly and require cultivation to keep down the 
 weeds. One 40-acre planting of sesbania in Imperial Valley in 1931 
 cost $5.38 per acre up to the time that it was plowed under. Sesbania 
 is plowed under without being disked previously. Notched disk plows 
 are commonly used to turn the rank growth under. The growing of 
 truck crops in beds and the "subbing" of the moisture to the plants 
 
 Fig. 4. — Plowing under sesbania in the Imperial Valley. Notches in the disk 
 are for catching and turning under the sesbania stalks. (Courtesy, F. G. 
 Beyschlag.) 
 
 tend to accumulate salts in the ridges. The flood irrigation required in 
 growing the sesbania counteracts this tendency by leaching the salts to 
 lower levels in the soil. Sesbania planted early in the season, plowed 
 under in July or August, and then irrigated, is practically all decayed 
 by the time lettuce is planted in October. 
 
 Sesbania also has certain disadvantages. It is susceptible to nema- 
 todes, requires high temperatures, an abundance of water, and does 
 not produce quite so much dry organic matter per acre as the other 
 summer legumes mentioned above. It may also serve as a breeding 
 ground for alfalfa caterpillars and cucumber beetles. Lettuce, how- 
 ever, being grown during the cool season of the year, suffers very little 
 from nematode attacks. The insects, particularly the alfalfa cater- 
 pillars, can be prevented from spreading to adjoining fields if the 
 
14 California Agricultural Extension Service [<^R- 60 
 
 sesbania is plowed under at a medium stage of maturity, before it 
 attains its full growth. The ease and cheapness of growing sesbania 
 may overbalance its lower production of dry organic matter. 
 
 Commercial Fertilizers. — Some growers plant green manure crops 
 and in addition use commercial fertilizers to keep the soil in a state of 
 high productivity. The three constituents supplied in a complete ferti- 
 lizer are nitrogen, phosphorous, and potassium. Any one or all of these 
 may be supplied in the organic or inorganic form. In the latter, the 
 elements are immediately available to the plant, while in the organic 
 form, the complex compounds must undergo decomposition into more 
 simple forms before they can be absorbed by the plant. This decom- 
 position or change is effected by different bacterial groups in the soil. 
 When the temperature of the soil is low, these bacteria function slowly 
 or not at all ; so it is better, during the cooler season at least, to apply 
 the fertilizers in the inorganic form. 
 
 No single kind or uniform amount of fertilizer can be specified for 
 the entire state or for any large district within the state. Each grower 
 should make a number of tests on his own farm to determine the kind 
 of fertilizers to use and the most profitable amount to apply. In gen- 
 eral, lack of nitrogen is usually what limits the growth of the lettuce 
 plant. Nitrogen can be applied in the inorganic form as nitrate of 
 soda, sulfate of ammonia, or calcium nitrate ; or in the organic form in 
 such compounds as tankage, fish meal, cottonseed meal, and dried 
 blood. A complete fertilizer is often broadcast, or drilled in after 
 plowing and before the beds are made, but may be drilled in the center 
 or in the sides of the bed before the seed is planted. Some growers 
 drill the fertilizer one or two inches below the seeds at the time of 
 planting, by use of special attachments on the seeders. Inorganic 
 nitrates may be applied immediately after the plants have been 
 thinned and until about a month before harvest. Their application 
 just after thinning and before the next irrigation, is usually to be 
 recommended. In the Imperial Valley, a side dressing, after thinning, 
 of 200 to 300 pounds of nitrate of soda per acre is the general prac- 
 tice. Often there is a second application of 150 to 200 pounds to the 
 acre. In the Los Angeles district nitrogenous fertilizers seem to be the 
 only kind needed. They may be drilled in along the side of the bed, as 
 shown in figure 5, or spread in the furrows before irrigations. One 
 should usually not apply large amounts of nitrogen after the heads 
 have started to form. The use of inorganic nitrogenous fertilizers 
 should be so timed as to pi'oduce a good growth before the heading 
 period. Too much available nitrogen at heading time may cause the 
 production of large, soft heads. Many of the soils of the state respond 
 
1932] 
 
 The Head-Lettuce Industry of California 
 
 15 
 
 more definitely to the addition to organic matter than to commercial 
 fertilizers. Even the nitrates cannot always be depended upon for the 
 desired results. 
 
 Some of the large growers in the Imperial Valley are now using 
 200 pounds per acre of treble superphosphate, analyzing 46 per cent 
 phosphorous pentoxide (PoOg). Heavier applications have, in many 
 cases, given even better results. This phosphate is broadcast on the 
 ground before the beds are listed or on the plowed sesbania ground 
 before it is disked and floated. 
 
 Fig. 5. — One type of drill used to apply fertilizer to the sides of the lettuce 
 beds. A plumber's "Y^' of two-inch pipe is fastened to the frame underneath the 
 fertilizer hopper of an ordinary combination corn planter and fertilizer drill. This 
 device facilitates a uniform distribution of the fertilizer along the sides of the 
 bed. (From Cir. 295.) 
 
 PREPARATION OF LAND PREVIOUS TO PLANTING 
 
 Leveling. — In the growing of lettuce under irrigation the land 
 must be level (fig. 6) and the beds of uniform height so that water can 
 be applied without flooding certain areas and leaving others high and 
 dry. Any leveling necessary should be done well in advance of the 
 planting season. If much soil has to be moved, a test irrigation had 
 best be made in order to settle it and to reveal the depressions and 
 elevations. The necessary retouching can be done after the soil has 
 become sufliciently dry. After leveling, manure or a commercial ferti- 
 lizer is often added to the places where the top soil has been removed, 
 so that a satisfactory crop will be produced. 
 
16 California Agricultural Extension Service [C^ir- 60 
 
 Preparatory Tillage. — In general, the soil should be plowed and 
 then disked and harrowed to a fine, mellow condition before the seed 
 beds are made. To make good beds or do good seeding on a cloddy soil 
 is difficult. When seeding is done during very hot weather, however, 
 aeration is facilitated and better stands are obtained if the soil is left 
 a little crumbly. 
 
 When alfalfa land in the Imperial Valley is broken up for lettuce, 
 it is given a deep plowing several months in advance and left in a 
 rough condition until about a month before planting. The land is next 
 floated, replowed, again floated, and then given a quick irrigation. 
 Sufficient time should be allowed after the first plowing to kill the 
 
 F^g. G. — A float used in leveling lettuce land in the ISalinas Valley. 
 
 Bermuda grass and alfalfa, and sufficient time after the second plow- 
 ing to float, border, flood, dry out the soil, disk, float, and make seed 
 beds in advance of the desired planting date. A common sequence of 
 operations for land that has just grown a cultivated crop is plowing 
 about eight inches deep, double disking and floating, and then replow- 
 ing, disking, cross-disking, floating, and bedding. In some districts 
 more operations may be necessary, the method of handling depending 
 a great deal on the type of soil. Chisel cultivators, adobe harrows, and 
 ring rollers are sometimes used in heavy soils. 
 
 Planting Practices. — Three general planting practices are employed 
 in growing lettuce in California. The crop may be seeded on level 
 ground, on raised beds in dry soil, or on raised beds in moist soil. 
 Planting without beds is. used only in a limited way in certain coastal 
 valleys where rain is the only source of moisture available. Under those 
 conditions seeding is done in rows 20 to 24 inches apart after the first 
 rains in the fall, and harvest is in the early spring. 
 
 Almost all the lettuce in California is planted on raised beds, which 
 facilitate irrigation and drainage and give good aeration about the 
 plants. The general custom is to grow two rows on a bed. 
 
1932] 
 
 The Head-Lettuce Industry of California 
 
 17 
 
 Making the Beds. — The width of bed, distance between beds, and 
 depth of furrow vary in different regions, according to the climatic 
 conditions and type of soil. The beds are 18 to 20 inches or more in 
 width, and the fnrrows 18 to 22 inches or more (fig. 8). Seldom are 
 the beds less than 3 feet from center to center, and usually they are 
 
 I- 
 
 Fig. 7. — Preparing the soil in the Salinas Valley for the fall crop of lettuce 
 after liarvest of the spring crop. The land is first disked and then either plowed 
 or deep-cultivated, as sho-svn above, to loosen the soil before the beds are made. 
 
 ^^ inches 
 
 -H<- - 20 mcfies 
 
 rour 
 
 rour 
 
 3"->| 14- inches ^ 3' 
 
 Ridqe or Bed 
 
 Fig. 8. — General tyj^e of bed and furrow used in the growing of lettuce in Cali- 
 fornia. Dimens'ons vary according to local conditions. (From Cir. 295.) 
 
 still farther apart. They should be 4 to 10 inches high after smooth- 
 ing. If the furrows are not sufficiently deep, there is danger of flood- 
 ing the beds. Inexperienced growers, as a rule, have a tendency to 
 make them too shallow. 
 
 The rough beds are made with a single lister pulled by two horses, 
 or with a double or triple lister pulled by a tractor, as shown in figures 
 
18 
 
 California Agricultural Extension Service [C^ir- 60 
 
 9 and 10. The rough beds may be shaped with a harrow or sled just 
 before seeding or with the planter sled at time of seeding. For very 
 hard and cloddy soil, special equipment must often be devised to 
 pulverize the beds so that they can be seeded. 
 
 Fig. 9. — Making lettuce ridges with single and double listers. (From Cir. 295.) 
 
 Fig. 10. — Making lettuce beds for a fall crop in the Salinas Valley with a triple 
 lister. The beds are irrigated before seeding. 
 
1932] 
 
 The Head-Lettuce Industry of California 
 
 19 
 
 VARIETIES AND STRAINS 
 
 The only variety of lettuce grown for commercial shipment in Cali- 
 fornia is the New York, known to the trade as "Iceberg." The true 
 Iceburg variety, however, although similar to New York in habit of 
 growth, has leaves of a reddish tinge. 
 
 No less than ten different strains of New York lettuce are now 
 being offered for sale, and new ones are constantly being added (fig. 
 
 Fig. 11. — A specimen of New York lettuce, the only variety shipped from 
 California in quantity. (From Cir. 295.) 
 
 11). Though all these strains have certain desirable characteristics, 
 they do not all thrive equally well under the same set of conditions, 
 and the grower often has difficulty in selecting the best strain for his 
 particular conditions. 
 
 The commercial New York strains can be grouped into three gen- 
 eral classes, based on disease resistance: (1) those susceptible to 
 mildew and brown blight; (2) those resistant only to brown blight, or 
 "single resistant"; and (3) those resistant to both mildew and brown 
 blight, or "double resistant." All the resistant strains are designated 
 
20 California Agricultural Extension Service [Cir. 60 
 
 by the name Imperial; numbers indicate the single-resistant and 
 letters the double resistant types. 
 
 Strains Susceptible to 3Iildew and Brown Blight. — New York 
 Eegular : For many years what was generally known as New York 
 Eegular or New York Special was the only seed planted. It has been 
 improved from year to year and under favorable conditions produces 
 a high percentage of uniform, good-quality heads. It is grown to some 
 extent in all districts where the soil is not infected with brown blight. 
 
 New York No. 12 : This, a selection out of New York Regular, is an 
 early low-heading strain, slightly lighter in color than New York 
 Regular. It is very uniform in appearance and in time of heading. 
 The head is exposed, as there are very few wrapper leaves. It heads 
 well during warm weather and stands considerable heat. Although not 
 so subject to tipburn and slime as some other strains, it is by no means 
 immune. No. 12 has been a great favorite with growers during the last 
 few years. 
 
 New York No. 41 : This, a selection out of New York Regular, has 
 an abundance of wrapper leaves of a deep green color. In early 
 growth, the head formation is well covered and has a pointed appear- 
 ance. It requires a few days longer to mature than No. 12, and it 
 yields best if matured during the winter and for the main spring and 
 fall crops. 
 
 Strains Resistant to Brown Blight .—Thefie strains and those of the 
 following group have been developed mainly by Dr. I. C. Jagger of the 
 United States Department of Agriculture. 
 
 Imperial No. 2 : One of the first strains developed for resistance to 
 brown blight was Imperial No. 2. This strain has produced satisfac- 
 tory yields in the Imperial Valley, but not along the coast. It is very 
 irregular in heading and will not stand warm weather. 
 
 Imperial No. 3 : This strain, which is slightly larger than Imperial 
 No. 2, has a tendency to be puffy. Satisfactory yields have been 
 obtained in the Imperial Valley, but not under warm weather con- 
 ditions. It is very little grown at the present, even in Imperial Valley. 
 
 Imperial No. 6 : The outer leaves of this strain tend to spread and 
 to grow close to the ground, exposing the head. It has a dark green 
 color and it matures late. Like Imperial No. 2 and No. 3, it heads best 
 under winter conditions. A few excellent crops have been produced on 
 the coast in the early spring and late fall, but in general it does not 
 produce satisfactorily under warm conditions. 
 
 The above strains of Imperial are distinct lines, having originated 
 from three individual parent plants. 
 
1932] The Head-Lettuce Industry of California 21 
 
 Imperial No. 2-50 : This, a selection out of Imperial No. 2, is very 
 uniform in size and heading" characteristics, has given good results 
 in the Imperial Valley for winter harvest and on the coast for early 
 spring and late fall harvest. Like the other single resistant strains, it 
 will not stand high temperatures and should not be planted for 
 harvest during warm weather. 
 
 Strains Resistant to Both Mildetv and Brown Blight. — These 
 strains, which are double-resistant, are designated by letters. 
 
 Imperial C : This is a black-seeded strain, 100 per cent resistant 
 to both brown blight and mildew; it attains good size but will not 
 stand warm weather. 
 
 Imperial F : This strain is slightly smaller than C but more 
 uniform in heading; it stands warm weather better than any of the 
 other resistant strains, enduring heat as well as New York Regular 
 and possibly as well as No. 12. Satisfactory yields have been obtained 
 under late spring conditions in the Salinas-Watsonville district. 
 Imperial F is very similar to New York Regular in type and soil and 
 climatic adaptations. 
 
 Imperial D : This is one of the latest double-resistant strains still 
 being tested in an experimental way. It is dark green in color, large, 
 and very firm. The texture is rather coarse. 
 
 TIME OF PLANTING 
 
 Lettuce requires from 70 to 150 days to mature, according to soil 
 and climatic conditions. The longest time is required for lettuce 
 planted in early winter ; and the shortest time for plantings made for 
 late summer or early fall harvest. 
 
 In the Imperial Valley, seeding is done during the fall, and 
 harvest takes place in the winter. During the remainder of the year 
 the land is used for other crops. 
 
 In the interior valleys and south coastal districts an early spring 
 and a late fall crop is possible ; the spring crop being planted during 
 the winter months and the fall crop in late summer. 
 
 In the Salinas-Watsonville district, where cool, foggy conditions 
 prevail during the summer, lettuce can be successfully matured during 
 any time of the year except from late December to the latter part of 
 March. In this district three crops of lettuce can be matured on the 
 same land in a single year; usually, however, only two crops are grown. 
 
22 
 
 California Agricultural Extension Service [Cir. 60 
 
 SOWING THE SEED 
 
 Various tools have been devised for sowing. The two rows on top 
 of the bed may be sown in a single operation by implements similar to 
 those shown in figures 12 and 13, but a gang of four planters can be 
 used if the two beds have been made at the same time, as shown in 
 figure 14. This system spaces the rows evenly and thereby facilitates 
 cultivation on top of and between the beds. 
 
 Fig. 12. — Planting two rows at one time. Sleds should be designed to smooth 
 the top of the bed, to firm the soil so as to provide a good seed bed, and to carry 
 the seed drills so that the seed is planted at a uniform depth, and at a uniform 
 distance from the center of the furrow. (From Cir. 295.) 
 
 Lettuce seed, being very small, should be sown shallow, but suffi- 
 ciently deep to be in contact with moisture. It will not germinate at 
 high temperatures unless the soil is well aerated. During warm 
 weather this aeration is accomplished by leaving the seed bed slightly 
 coarser than during the cool season of the year. According to Borth- 
 wick and Robbins,* if lettuce seed is to be planted in a soil which has 
 a temperature of 86° Fahrenheit or more during many hours of the 
 day, good germination can be obtained by placing the seed in thin 
 layers between moist burlap and then storing on ice for four to six 
 days. Good aeration must be provided during this storage period. 
 When the seed is dried and planted in moist soil, a high percentage of 
 germination is obtained. 
 
 4 Borthwick, H. A., and W. W. Bobbins. Lettuce seed and its germination, 
 Hilgardia 3:275-304. 1928. 
 
1932] The Head-Lettuce Industry of California 
 
 23 
 
 Fig. 13. — Two-row lettuce planting sled. Note the four rolling cutters and the 
 two shoes in front of each seed drill. The former pulverizes the clods, and the 
 latter firms the soil in front of the drill. (From Cir. 295.) 
 
 Fig. 14. — Four-row lettuce planter in operation in the Salinas Valley. 
 The beds were irrigated before seeding. 
 
24 California Agricultural Extension Service [^^- ^^ 
 
 Very thick seeding is objectionable. The labor cost of thinning 
 the thick stand of plants is expensive, and there is the additional waste 
 of high-priced seed. From 1 to IV2 pounds of seed to the acre is 
 sufficient if all the seed is viable and if the soil temperature and 
 moisture conditions are favorable. Even under favorable conditions, 
 however, the use of a little more seed may give a better stand. 
 
 The distance between rows should not be less than 10 inches. 
 Some growers space the rows from 15 to 17 inches apart to give room 
 for the development of large heads. When the rows are too close 
 together on top of the bed, cultivation is more difficult, various 
 diseases are likely to develop, and the mature heads are usually 
 smaller. On the other hand, the plants usually grow better if not too 
 near the edge of the bed. 
 
 If a large acreage is being grown, successive sowings should be 
 made at intervals of 10 to 14 days throughout the lettuce-planting 
 season. In some lettuce-growing projects, planting is continuous 
 throughout the planting period, except when interrupted by adverse 
 weather. 
 
 IRRIGATION AT PLANTING TIME 
 
 The system of irrigation used at the time of planting varies with 
 the locality and with the climatic and soil conditions. In some 
 regions the land is flood irrigated, the beds are made, the seed planted, 
 and no further irrigation is given until the seedlings are through the 
 soil. This system can be practiced where the soil dries out slowly. 
 Beds of moist soil settle more evenly after irrigation than those made 
 of loose, dry soil, so that preliminary flooding is advantageous. 
 
 Where evaporation is very high it is customary, in addition to the 
 preliminary flood irrigation, to irrigate immediately after planting or 
 as soon as germination is desired. 
 
 Rough beds are sometimes made in land that has not received a 
 preliminary flooding. The beds are wet by running water in the 
 furrows, as shown in figure 15. This irrigation moistens and settles 
 the beds, which, when sufficiently dry, are smoothed and planted. 
 This is the general practice in the Salinas-Watsonville district. 
 
 The fall crop of the interior valleys is usually planted in dry 
 soil and then not irrigated until the grower desires to start the 
 germination of the seed. 
 
 The following plan is sometimes used for the early plantings in 
 the Imperial Valley : a preliminary flood irrigation is given, the beds 
 
1932] 
 
 The Head-Lettuce Industry of California 
 
 25 
 
 are made, and then irrigated. The tops of the beds, as soon as suffi- 
 ciently dry, are harrowed with a special tool equipped with runners 
 which slide in the furrows and prevent their being filled with clods. 
 
 Fig. 15. — Irrigating lettuce beds before seeding, in the Imperial Valley. Water 
 enters the furrows from the head ditch through small conduits. Usually only one 
 is used for each furrow. The piece of shook beside the opening is used to regulate 
 the flow. (From Cir. 295.) 
 
 Fig. 16. — The seed has been planted, and the beds are being irrigated. Irriga- 
 tion immediately after planting is an important operation in most of the lettuce- 
 producing areas of California. (From Cir. 295.) 
 
 Seeding is started a few hours later, as soon as the soil is dry enough 
 for the planter to operate. The land is irrigated again, as soon after 
 seeding as possible. 
 
26 
 
 California Agricultural Extension Service [CiR- ^^ 
 
 In furrow irrigation, the water should be allowed to *'sub" until 
 it finally moistens the entire bed. Irrigating the beds immediately 
 after planting, as shown in figures 16 and 17, is usually preferred in 
 warm, dry weather. The water is often kept running in small streams 
 down the furrows until the plants are up, in order to cool the soil 
 and produce a high percentage of germination if the water is cooler 
 than the soil. In cool weather such heavy irrigation immediately after 
 planting is unnecessary. In heavy clay soils, deep furrows are used 
 
 Fig. 17. — Irrigation and drainage ditches. The drainage ditch at the right is 
 carrying off the water which has passed down between the beds. The irrigation 
 ditch at the left is ready to receive water and conduct it to the furrows between 
 the beds. A more uniform control of moisture conditions can be obtained if the 
 rows are not too long. Cross ditches for irrigating and drainage facilitate the 
 equable distribution of water. (From Cir. 295.) 
 
 with a small head of water. If the water comes up close to the top of 
 the bed, the soil will bake and crack when it dries, and the seedlings 
 will not come through. 
 
 Regardless of location, however, the surface soil should be kept 
 moist until after the seedlings are through the ground. In the hot 
 interior valleys more care is needed to keep the surface soil moist than 
 along the coast, where the moist air and cool temperatures prevent 
 rapid evaporation. The time of irrigation depends mainly upon the 
 size of the plant and upon the climatic and soil conditions. 
 
1932] The Head-Lettuce Industry of California 27 
 
 THINNING AND HOEING 
 
 Lettuce should be thinned before the plants begin to crowd. In 
 warm weather this time may be three weeks after planting, but in 
 cool weather thinning may be delayed as long as eight weeks. The 
 plants are blocked out 12 to 15 inches apart in the row with special 
 short-handled hoes and at the same time are thinned by hand to one 
 in a place, as shown in figures 18 and 19. Plants not true to type 
 should be removed at this time. The plants should have plenty of 
 room in the row. 
 
 Fig. 18. — Thinning lettuce in the Salinas Valley. Plants are spaced 
 about 12 inches apart. 
 
 Thinning is a very important operation; and in many cases when 
 it is done under contract, a part of the money is withheld until the 
 job is finished in a satisfactory manner. Beds and furrows are usually 
 cultivated before thinning. Growers often stipulate that all weeds 
 left by the cultivator shall be removed by those doing the thinning, 
 that the plants shall stand at a specified distance in the row, and that 
 no doubles shall be allowed to remain (fig. 20). Many growers, how- 
 ever, have the weeds and doubles removed in a separate operation. 
 When there is danger of damage by insects, thinning should be 
 delayed, if possible, until the pests have been destroyed. 
 
28 
 
 California Agricultural Extension Service [Cir. 60 
 
 k^t f'^^'^2 
 
 Fig. 19. — ^Thinning lettuce. Single plants are left at distances of about 12 inches. 
 Blocking is done with a short-handled hoe. (From Cir. 295.) 
 
 Fig, 20. — An excellent stand of young lettuce for early fall harvest in the Salinas 
 Valley. The plants have been thinned and the beds cultivated. 
 
1932] The Head-Lettuce Industry of California 29 
 
 IRRIGATING THE GROWING CROP 
 
 The details of irrigation vary considerably in different localities 
 and at different times of the year. Small plants need much less water 
 than large ones. Less water is required when the weather is cool and 
 humid than when it is hot, dry, and windy. The frequency of irri- 
 gation also depends on the water-holding capacity of the soil: as a 
 rule, more frequent irrigations are needed on light, sandy soils than 
 on silt or clay-loam soils, which are more retentive of moisture. Most 
 growers believe that water should not be applied when the heads are 
 maturing, since it has been observed that they are likely to be soft 
 and loose. Heavy rains just before cutting time also may cause the 
 development of open, spongy heads. 
 
 It takes some experience to know just when to irrigate, but as a 
 rule the plants are in need of water when they become dark green 
 and the leaves look and feel tough and leathery. "When the moisture 
 supply is plentiful, the leaves are crisp and are of a lighter green. 
 During frosty weather, some growers practice night irrigation in the 
 belief that the temperature of the air around the lettuce is raised. 
 
 Most growers use a series of wooden conduits or flumes to carry a 
 small stream of water from the end ditch to the furrows between the 
 beds. A conduit is made of four laths or slightly wider strips, such 
 as cantaloupe shook, 20 to 24 inches long, nailed together. The conduit 
 should be sufficiently long to fit well in the ditch bank. Pieces of 
 shook or lath can be placed in front of the conduits to regulate the 
 flow. Galvanized or iron pipes cut to the same length as the wooden 
 conduits are often used. Iron lasts longer. Sizes from li/o to 1% 
 inches in diameter are generally used. 
 
 CULTIVATION 
 
 It is often desirable to cultivate in order to open the furrow and 
 in order to replace the soil around the young plants after thinning 
 (fig. 21). Later cultivations may be necessary to destroy weeds which 
 rob the soil of moisture and soil nutrients but, beyond this point, 
 cultivation is not necessary or even beneficial. Certain soil conditions, 
 however, may require special consideration. The ordinary beet or 
 bean cultivator gauged for either one or two beds is satisfactory. 
 Power cultivators covering as much as three beds at a time are coming 
 
30 California Agricultural Extension Service [Cir. 60 
 
 into use. To insure close cultivation to the plant without injury, the 
 grower must make the number of beds cultivated in a single operation 
 correspond to the number of beds seeded at one time. 
 
 Fig. 21. — A four-row or two-bed cultivator in operation in the Salinas Valley. The 
 number of rows cultivated corresponds to the number seeded at a single operation. 
 
 YIELD 
 
 According to the Federal and State Market News and Crop Report- 
 ing Service covering the past few years, production of lettuce for 
 California has averaged slightly in excess of one-half carload for each 
 acre seeded. A total crop failure because of insects, diseases, loose 
 heads, or poor market conditions is not uncommon. 
 
 HARVESTING 
 
 Harvesting should not take place until the heads are hard. Growers 
 show a tendency at times to harv^est lettuce too soon, especially if the 
 price is high. Most of them now realize, however, that money is 
 usually lost by premature harvesting: immature heads wilt more 
 readily, and not only sell for less but also ruin the market for the 
 high-grade product. When ready to cut, the tops of the mature heads 
 are lighter colored than those of the immature, and have a silvery 
 appearance. 
 
 Lettuce should not be cut for shipment immediately after a rain 
 or an irrigation, or before the frost and dew are gone in the morning. 
 
1932] 
 
 The Head-Lettuce Industry of California 
 
 31 
 
 Harvesting should, furthermore, not be done when the field is muddy. 
 Then the plants are gorged with water, the leaves are crisp and 
 brittle and break easily in handling ; if just slightly wilted, they are 
 injured less in handling and packing, and consequently will carry 
 better in transit. 
 
 
 Fig. 22. — Harvesting lettuce, showing the type of knife used and the method 
 of cutting off the root just below the ground. (From Cir. 295.) 
 
 Fig. 23. — Harvesting summer-grown lettuce in the Salinas Valley. The heads 
 are cut and placed in rows. They are then packed in field crates for hauling to the 
 lettuce-packing sheds. 
 
 Lettuce should be cut just below the surface of the ground, as is 
 shown in figure 22. Most of the trimming of the outer leaves should 
 be done at the packing shed. 
 
32 
 
 California Agricultural Extension Service [Cir. 60 
 
 Harvesting is usually done by contract labor. A gang of men go 
 down the rows, cutting the matured heads and tossing them into the 
 furrows (fig. 23). A second crew then pack the heads tightly into 
 crates with the stems up ; the crates are then loaded on trucks and 
 hauled to the packing shed (fig. 24). 
 
 Lettuce heads that show signs of development of a seed stalk, that 
 have burst, or that have tipburn, should be discarded in the field. 
 
 1^'*' 
 
 F'g. 24. — Loading field crates of lettuce for hauling to the packing shed. 
 
 Growers should not attempt to harvest all the heads in a field at 
 one cutting. As a rule, one must make more than one cutting in order 
 to obtain all heads at the best stage of maturity. 
 
 Lettuce should not be delivered to the packing shed in a badly 
 wilted condition. When the haul to the packing shed is long, crates 
 should be covered with heavy muslin or canvas. The crates in the 
 field, furthermore, should not be filled too full, or the lettuce will be 
 bruised and crushed. 
 
 In very warm weather or when freezes are expected, lettuce should 
 be harvested as soon as it is hard. When the weather is cool, mature 
 lettuce can remain in the field for some time without bursting. As a 
 rule, however, it should not be held long at any time, if it is to be 
 marketed in good condition and with a minimum of waste. 
 
1932] 
 
 The Head-Lettuce Industry of California 
 
 33 
 
 PACKING FOR SHIPMENT 
 
 At the packing" shed, the loose, diseased, and damaged leaves are 
 trimmed off, as shown in figure 25, and the small heads and loose 
 heads are culled out. The tendency at present is to remove more of 
 
 Fig. 25. — Trimming lettuce. The butts and damaged or diseased leaves are 
 trimmed off. The waste leaves are used for poultry, cattle, or hog feed. (From 
 Cir. 295.) 
 
 the wrapper leaves than was formerly the practice. When trimmed, 
 the heads are tossed to the packing table, where they are placed in 
 the Standard California lettuce crate, as shown in figure 26. Twenty- 
 
34 
 
 California Agricultural Extension Service i^^- ^^ 
 
 four, 30, 36, 42, 48, 60, 75, or 90 heads are put in each crate, depend- 
 ing upon their size. The growers and shippers, however, usually 
 prefer to have heads that pack 4 and 5 dozen to the crate. 
 
 rig, 26. — Packing- and trimming in the packing shed. In the background the 
 men are cutting back the stems and removing the diseased and damaged leaves. 
 The trimmed heads are then tossed to a low table in reach of the packers. (From 
 Cir. 295.) 
 
 Fig. 27. — Cracked ice is placed between the layers of lettuce when packed. 
 From 25 to 30 pounds of ice are used in each crate. This cools the lettuce and 
 tends to insure its reaching the eastern markets in good condition. (From Cir. 
 295.) 
 
 The lettuce crate is lined with two strips of heavy waterproofed 
 paper, which cover the bottom, sides, and ends, and fold over the top. 
 This lining protects the heads from dirt and infection, keeps them 
 
1932] 
 
 The Head-Lettuce Industry of Caltfornia 
 
 35 
 
 cool and fresh, and guards them against mechanical injury. Three 
 layers of heads are packed tight in the crate with stems up, generally 
 with cracked ice between the layers, as shown in figure 27. Usually 
 not over 30 pounds of ice is used in each crate. The crates should be 
 placed in the refrigerator car as soon as they are packed. From 
 4,500 to 7,500 pounds of ice, depending upon the weather, is placed 
 in the car, usually on top of the crates (fig. 28) instead of in the 
 bunkers. The use of ice on top of the load preserves the ice in the 
 crates, thus keeping the lettuce fresh for a long time. 
 
 Fig. 28. — Loading car with lettuce. Crates are stacked 4 deep, 5 wide, and 16 
 long, and are held firm by wooden strips. Ice is placed on top of the upper tier of 
 crates. The figure also shows a packed crate with the desirable bulge. (From 
 Cir. 295.) 
 
 FEDERAL STANDARDS FOR HEAD LETTUCE 
 
 The U. S. Standard grades for lettuce formulated by the Bureau 
 of Agricultural Economics, United States Department of Agriculture, 
 as of December 1, 1926, are as follows : 
 
 * ' U. S. No. 1 shall consist of heads of lettuce of similar varietal characteristics 
 which are fresh and well trimmed; which are not decayed, split or burst, and 
 which are free from seed stems and doubles and from damage caused by dirt, 
 wilting, freezing, tipburn, disease, insects, or mechanical or other means. The 
 appearance of the wrapper leaves shall not be seriously affected from any cause. 
 Not less than 75 per cent of the heads of Iceberg type lettuce shall be firm and 
 the remainder shall be fairly firm. Heads of Big Boston type lettuce shall be 
 fairly firm. 
 
 In order to allow for variations, incident to proper grading and handling, 
 not more than 10 per cent by count, of any lot, may be soft or otherwise below 
 
36 California Agricultural Extension Service [Cir- 60 
 
 the requirements of this grade, but this tolerance shall not permit in any lot of 
 Iceberg type lettuce fewer than 75 per cent of heads which are firm and free 
 from defects not allowed in U. S. No. 1. 
 
 U. S. No. 2 shall consist of heads of lettuce of similar varietal charaeteristics 
 which are fresh, which are not decayed, split, or burst, and which are free from 
 seed stems and from damage caused by wilting, tipburn, disease, insects, or 
 mechanical or other means and from serious damage caused by freezing. 
 
 In order to allow for variation incident to proper grading and handling, 
 not more than 10 per cent, by count, of any lot may be below the requirements 
 of this grade. 
 
 U. S, Fancy shall consist of heads of lettuce of similar varietal characteristics 
 which are fresh and well trimmed, and which are not decayed, split or burst, 
 and which are free from tipburn, seed stems, and doubles, and from damage 
 caused by dirt, wilting, freezing, disease, insects, or mechanical or other means. 
 The wrapper leaves shall be of a good green color and free from damage from 
 any cause. Not less than 50 per cent of the heads of Iceberg type lettuce shall be 
 hard and the remainder shall be firm. Heads of Big Boston type lettuce shall 
 be firm. 
 
 In order to allow for variations incident to proper grading and handling not 
 more than 10 per cent, by count, of any lot may be soft or otherwise below the 
 requirements of this grade, but this tolerance shall not permit in any lot of the 
 Iceberg type lettuce fewer than 50 per cent of heads which are hard and free 
 from defects not allowed in U. S. Fancy. ' ' 
 
 CALIFORNTA STANDARDS FOR HEAD LETTUCE 
 
 All head lettuce offered for sale in California must comply with 
 the provisions as set forth in the California Fruity Nut and Vegetable 
 Standardization Act of 1931. 
 
 "Section 32. — Standard for head lettuce. Head lettuce shall not be leafy 
 without head formation and shall be free from slime, decay or rot affecting leaves 
 within the head, internal insect injury, and free from seed stems which have so 
 developed that they are apparent upon external examination ; and free from 
 serious damage, as defined in this section caused by bursting or freezing. Damage 
 caused by bursting shall not be considered serious unless the head is burst 
 open or is materially misshapen from this cause. Damage caused by freezing 
 shall not be considered serious unless it affects any portion of the head inside 
 the six outer leaves. 
 
 In order to allow for variation incident to proper grading and handling, not 
 more than 10 per cent by count, of the heads of lettuce in any one container 
 or bulk lot may be below these requirements, but not to exceed one-half of this 
 tolerance, or 5 per cent, shall be allowed for any one cause. 
 
 In addition to the other requirements specified in this section head lettuce, 
 when packed, shall be virtually uniform in size which shall mean a variation 
 in any container of not more than 10 per cent of heads which would pack a. 
 size, larger or smaller, than the size marked, and they shall be tightly packed 
 which shall mean that it is not possible without damaging or injuring the lettuce, 
 to place additional heads in any of the layers of heads in the container. 
 
1932] The Head-Lettuce Industry of California 37 
 
 Head lettuce packed in ice shall be in standard container number 45, section 
 thirty-eight to the contrary notwithstanding'; however, other size containers may 
 be used if conspicuously marked on the outside of the end which bears any marks 
 intended to describe the contents of such container, in letters and numbers not 
 less than one-half inch in height with the inside width in inches directly preceded 
 by the word ''width" and the inside length in inches, directly preceded by the 
 word * ' length. ' ' 
 
 Section 38. — Head lettuce, when packed as a standard pack and so marked, must 
 in addition to other packing requirements of the California Nut, Fruit and Vege- 
 table Standardization Act of 1931, contain either two dozen, two and one-half 
 dozen, three dozen, three and one-half dozen, four dozen, five dozen, seventy-five 
 or ninety heads of lettuce per standard container number 45, with a slight bulge 
 of crates when lidded. Each crate of three and one-half dozen count shall have 
 each layer arranged with four rows of three, four, and four and three heads. 
 In the case of sizes seventy-five and smaller per crate, a bridge of from three to 
 six heads shall be permitted and in the five dozen size a bridge of four heads 
 shall be permitted. 
 
 The standard lettuce crate number 45 has an inside depth of 13 inches, inside 
 width of 18 inches, and an inside length of 21% inches." 
 
 FEDERAL-STATE INSPECTION 
 
 The following brief synopsis of the history, function and scope of 
 the Federal-State inspection service is taken from Special Publication 
 32 of the California State Department of Agriculture : 
 
 "In July, 1920, there was established in California a commercial shipping- 
 point inspection service carried on by the Bureau of Standardization of the 
 State Department of Agriculture. This service employs a corps of experienced, 
 highly trained men who are authorized to inspect and certify to the exact 
 quality and condition of the produce at time of packing and shipping. The 
 demand for this service has increased steadily, and its scope and importance has 
 been greatly enlarged .... On July 1, 1922, this service was federalized, each 
 inspector being deputized by the federal government, and certificates are now 
 prima facie evidence in all courts of the United States. 
 
 This inspection is available in all of the leading vegetable-produ,eing sections 
 of the state. The certificate shows the hour and date of inspection, inspection 
 or shipping point, name and address of the shipper and consignee (when given), 
 car initials and number, kind of car and its condition ; if a refrigerator, the 
 amount of ice in the bunkers ; the quantity of the products inspected ; description 
 of load and container ; condition of pack ; sizing, quality, and condition of the 
 product at the time the car is loaded, although he may be at a considerable 
 distance from the shipping point. These shipping-point certificates are valuable 
 to the grower, as they protect his interests in the adjustment of claims or on a 
 declining market. On the other hand, the buyer is assured that he will receive 
 the quality of produce for which he has paid before seeing it. Whenever requested, 
 a telegram giving the substance of an inspection will be sent ''collect" to the 
 buyer or any other interested party, so that the exact condition of a carload 
 can be ascertained before the sale is even consumated. ' ' 
 
38 California Agricultural Extension Service l^^^ ^^ 
 
 UTILIZATION OF CULL LETTUCE 
 
 In the process of packing, large quantities of leaves and cull heads 
 accumulate. The leaves analyze 94.7 per cent water, 1.27 per cent 
 protein, 0.3 per cent fat, 2.9 per cent carbohydrates, 0.7 per cent fiber, 
 and 0.9 per cent ash. Although this material is usually dumped as 
 waste, it has proved to be a fair feed for range cattle during the 
 season of the year when there is a shortage of feed on the range. In 
 August, September, and October of 1930, H. and N. Silacci, cattlemen 
 of the Salinas Valley, fed 500 head of mixed range cattle entirely 
 
 Fig. 29. — Feeding beef cattle in the Salinas Valley on cull lettuce 
 and leaves obtained from the packing sheds. 
 
 on cull lettuce (fig. 29). The animals made fair gains, and the only 
 harmful effect noticed was that a few of them bloated ; there were no 
 losses. After about 70 days on this feed, 90 cows were sold for beef, 
 these dressing out approximately 52 per cent. These 90 cows gained, 
 according to an estimate, about 200 pounds per head during this 
 period. Mature cows eat from 100 to 125 pounds of lettuce per day, 
 when on full feed. 
 
 Cull lettuce is also being used successfully as a food for dairy 
 cows. C. Higgins, a dairyman in the Salinas district, fed his cows 
 for three months on cull lettuce supplemented with oat hay. The cows 
 milked well on this ration and maintained fair condition. The butter- 
 fat content of the milk remained about the same as when the herd 
 was fed on silage and oat hay. 
 
1932] The Head-Lettuce Industry of California 39 
 
 Not only is lettuce a desirable feed for cattle, but it is also economi- 
 cal. The problem which confronts most cattlemen in feeding" cull 
 lettuce is to secure a continuous supply to carry their herd for a 
 period of two or three months. 
 
 INSECT PESTS AND THEIR CONTROL 
 
 Cutworms. — Probably the most serious pest of lettuce is the cut- 
 worm, which usually cuts off the young plants at the ground level. 
 The best control has been obtained by the use of poisoned bait. The 
 following formula is recommended : 
 
 Paris green (or white arsenic) 1 pound 
 
 Molasses (cheap blackstrap) 2 quarts 
 
 Water 15 to 20 quarts 
 
 Dry bran 25 pounds 
 
 The poison should be thoroughly mixed with the bran. Each 
 particle of bran must carry some poison in order to get a good kill. 
 When making small quantities, one can mix the bait in a bucket with 
 a paddle, adding the poison slowly and stirring in the bran at the 
 same time. Or, the poison and bran can be mixed with the hands if 
 the latter are free from cuts, scratches, or other wounds. When 
 making large quantities, one can mix the poison with the bran on 
 some flat, smooth surface, using a shovel and rake as in mixing 
 concrete. 
 
 The syrup should be mixed with the water, then well stirred into 
 the bran and poison mixture. Large quantities of liquid added at 
 one time will wash the poison from the bran, resulting in an uneven 
 mixture; only enough should be added to make a crumbly mash. A 
 little of the mixture of dry bran and arsenic may well be set aside 
 so that if too much liquid is added the dry reserve can be used to 
 give the proper consistency. 
 
 This mash should be spread on top of the beds near the plants in 
 the early evening, as cutworms do most of their feeding at night. 
 Ten to fifteen pounds of the wet bait per acre is enough for one 
 application. Two or three applications at two-day intervals may be 
 needed to rid the field of the pest. When young, the plants may be 
 dusted or sprayed with calcium arsenate, but not when approaching 
 maturity. 
 
 Grasshoppers. — Grasshoppers sometimes eat entire fields of young 
 fall-planted lettuce. Damage from them may be expected where 
 lettuce fields are adjacent to alfalfa or pasture lands; these fields 
 
40 California Agricultural Extension Service [C^ir- 60 
 
 should, if possible, be thoroughly disked or harrowed during the 
 winter. Alfalfa land which is being broken up for lettuce, should be 
 disked and harrowed before plowing, to destroy the eggs of grass- 
 hoppers and other insects and the pupal stages of cutworms. All 
 growers, in addition, should make a regular practice of burning the 
 grass and weeds, and working the ground along the roads and ditch 
 banks adjoining their fields, for the grasshoppers lay their eggs in 
 the surface of the soil of these untilled areas. 
 
 When grasshoppers appear in the field, a heavy irrigation should 
 be given to moisten the ground thoroughly. The best means of control 
 is to use the poison bran mash recommended for cutworms, with the 
 addition of 18 chopped lemons and 1 pound of salt. The substitution 
 of 14 pound of sodium arsenite for the paris green is also recom- 
 mended. This mash should be spread in the early morning, because 
 grasshoppers do most of their feeding during the day. 
 
 Alfalfa Senii-l 001)67'. — In the coastal districts, serious damage is 
 often done by the alfalfa semi-looper {Autographa calif ornica) . Eggs 
 are laid by the adult moth directly on the plant. In about ten days 
 these hatch into green larvae that propel themselves by looping the 
 body. In from four to six weeks the larvae attain their full size, 
 three-fourths to one inch in length, and leave the i^lant to pupate in 
 the soil. This insect is sometimes present in small numbers before 
 thinning. After thinning, the larvae congregate on the remaining 
 plants, often devouring all the foliage. The most serious injury is 
 destruction of the terminal bud, which prevents the development of 
 new leaves. 
 
 Unless the larvae are present in large numbers when the lettuce is 
 heading, they usually cause only slight damage, because they leave 
 the plant before it matures, so that the head develops normally. On 
 mature plants injury is primarily from the dead tissue of the leaves, 
 which makes the plant susceptible to slime rot. 
 
 Control of the semi-looper can be effected by spraying with a mix- 
 ture made of 3 pounds of lead arsenate to 100 gallons of water, or 
 by dusting with a 20 per cent lead arsenate, calcium arsenate, or zinc 
 arsenite mixture at the rate of 30 pounds per acre. Barium fluosilicate, 
 6 pounds in 25 pounds of talc dust, has given excellent control and 
 has an advantage over arsenical compounds in that it is not poisonous 
 to human beings and can be used on much older plants without 
 danger. Sodium fluosilicate is not recommended because under certain 
 climatic conditions it is likely to cause burning. Poisonous dusts and 
 sprays should not be applied after the lettuce heads are more than 
 one-third developed. 
 
1932] The Head-Lettuce Industry of California 41 
 
 Caterpillars, — Injury from caterpillars is usually confined to 
 lettuce planted adjacent to alfalfa fields, ditch banks, or weed patches. 
 The caterpillars hatch in these areas and when mature move into the 
 lettuce field in search of a place to pupate, devouring' plants in their 
 path. Control by poisoning" is difficult because of the maturity of 
 the larvae. Barium fluosilicate, 30 per cent in talc, has at times given 
 control. If abundant, caterpillars can be trapped in a trench dug 
 with the steep side toward the lettuce. 
 
 Aphis. — Of the two species of aphis prevalent on lettuce, one is 
 found on the leaves and the other on the roots. Both are somewhat 
 similar in appearance. The leaf aphis, if abundant, checks the growth 
 of the youn^ plants by sucking" out the juice. In the mature plants, 
 the honeydew secretion deposited on the leaves by the aphis makes 
 the lettuce unfit for market. 
 
 The root aphis is found clinging in cotton-like masses to the roots 
 or in the adjacent soil. As the numbers increase the plants become 
 yellowish and unhealthy in appearance. During the warm part of 
 the day, they may wilt. Koot aphis are more abundant in heavy soils 
 that tend to crack and crumble than in the lighter, more sandy soils 
 that remain compact. 
 
 New infestations of both the leaf and root aphis start from winged 
 forms produced at certain stages of the life cycle. The female gives 
 birth to living- young in large numbers. If unchecked, the infestation 
 may become general in the course of a few weeks. 
 
 Normally the leaf aphis is controlled by natural enemies. Preda- 
 ceous insects such as the larvae of the common ladybird beetle and 
 syrphid fly feed upon it. Some aphis are parasitized by insects and 
 thus destroyed. Under warm, humid conditions certain fungi likewise 
 tend to hold them in check. As a rule, serious outbreaks oecur only 
 during long- periods of cloudy, damp, or foggy weather which make 
 the natural enemies inactive. 
 
 The grower can control the leaf aphis by spraying with a nicotine 
 solution made of one pint of Blackleaf 40 to 100 gallons of water, or 
 by dusting with an 8 to 10 per cent nicotine dust. In the application 
 of dust mixtures, the dragging of a canvas trailer 8 to 12 feet long- 
 behind the duster to confine the dust to the plant for a few seconds 
 will be found advantageous. In both spraying and dusting-, one must 
 bring the material in direct contact with the insect. This procedure 
 is often difficult, because most of the insects oecur on the underside 
 of the leaf. 
 
 The control of root aphis is extremely difficult because one cannot 
 apply any material direct to the insect at a reasonable cost. Damage 
 
42 California Agricultural Extension SERAacE l^^^- ^o 
 
 can be held to a minimum by frequent irrigation given to keep the 
 soil in an expanded condition and in close contact with the roots. An 
 abundance of moisture also allows the unaffected roots to keep the 
 plants in a good growing condition. Immediately after harvest, the 
 grower should plow or cultivate the field to destroy all plants that 
 might serve as a host to insects. 
 
 Wireivorms. — Wireworms are the larvae of click beetles. They are 
 yellowish-brown, segmented, and are from one-half to two inches long. 
 During the spring and summer they are close to the surface of the 
 soil and can be found feeding on a wide range of weeds and cultivated 
 plants. They pass the winter months deep in the soil. They injure 
 lettuce by burrowing and feeding in the taproot. If they find suffi- 
 cient food during the spring months, they may go deep into the soil 
 early in the year and not feed upon the fall crop. 
 
 The grower can control wireworms by attracting them with a trap 
 crop or bait and then destroying them with poisonous gas. The field 
 should be clean-cultivated and the soil well pulverized. The trap crop 
 or bait, such as old peas and beans, is drilled into the soil about four 
 inches deep ; and the wireworms soon congregate about it. In five to 
 eight days, granular calcium cyanide is drilled just over the bait at 
 the rate of 75 to 100 pounds per acre. The moisture in the soil reacts 
 with the calcium cyanide to form hydrocyanic acid gas which destroys 
 the wireworms. 
 
 Vegetable Weevil. — The vegetable w^eevil {Listroderes ohliquus) 
 is not a pest in any of the main lettuce-shipping districts of California. 
 It interests the lettuce grower only from the standpoint of certificates 
 of weevil inspection that must accompany shipments within the state. 
 
 In California, the weevil is found only in a limited area, being 
 confined to districts in the San Francisco Bay region. 
 
 The first adults of the vegetable weevil appear in March and feed 
 on the tops of various vegetable plants until June, when they enter an 
 aestivation period. They emerge from aestivation about September 
 and begin their egg laying, which usually continues, with varying 
 activity, until March and April. The larvae are present from October 
 to April, feeding on the tops and crowns of most vegetables. The most 
 destructive period is the winter, when the greatest number of larvae 
 are present. When mature, they enter the soil and form pupae in 
 small earthen cells, usually in the top soil. The adults emerge during 
 the spring. 
 
 Corn Earworm. — In the coastal district, at certain seasons of 
 the year, considerable damage is done to lettuce by the corn earworm 
 {Chloridea ohsoleta). The adult is a night-flying moth that emerges 
 
1932] The Head-Lettuce Industry of California 43 
 
 from the soil in the late spring. Eggs are deposited on lettuce and 
 other host plants. The eggs hatch in a few days and the young pro- 
 ceed to burrow into the host plant. In from 15 to 20 days the mature 
 larvae leave the plant and enter the soil to pupate. The moth emerges 
 in about 10 days to start a new generation. There are three or more 
 broods during the year, the last probably doing the most damage to 
 lettuce. 
 
 It is questionable if the corn earworm will multiply very rapidly 
 on lettuce alone, as it is one of the least attractive host plants. How- 
 ever, if other host plants, such as corn and tomatoes, are present it 
 will probably multiply rapidly. 
 
 Fig. 30. — Dusting lettuce in the early morning by airplane for the control 
 of leaf -eating insects. (Courtesy, Britton Eey.) 
 
 Materials that have showed promise in the control of the corn 
 earworm are zinc arsenite, and the fluosilicates. On the young beds 
 a 20 per cent zinc arsenite dust is used while on the older beds the 
 25 per cent dust mixtures of fluosilicates are used. The dusts are 
 applied at the rate of 35 pounds to the acre. It is necessary to have 
 a covering on the plant almost continuously during the growing 
 season because when once the insect penetrates the outer leaves it is 
 impossible to obtain control. The airplane is coming into use as a 
 means of spreading dusts for this and other leaf-eating insects, 
 (fig. 30). 
 
 After harvesting, infested fields should be plowed to turn under 
 the remaining plants. This will prevent the larvae in the heads from 
 maturing. Disking of infested fields is not sufficient because if the 
 heads are merely cut and allowed. to dry the conditions within them 
 are ideal for pupation. 
 
44 California Agricultural Extension Service [CiR. 60 
 
 BIRDS 
 
 In some sections of the state English sparrows often destroy many 
 acres of young lettuce. Probably the best method of control is to 
 place a large number of small scarecrows throughout the field in the 
 form of bright pieces of cloth or paper fastened to laths or sticks. The 
 use of a shotgun for a day or two will help to scare the birds away. 
 
 DISEASES AND THEIR CONTROL 
 
 Lettuce is no exception to the rule that with intensive propagation 
 of one crop, one or several serious diseases gradually become epi- 
 demic. In California, four diseases have become serious within the 
 past 18 years. Brown blight (cause unknown) has been present in 
 Imperial Valley since 1912. Downy mildew {Bremia lactucae) occurs 
 in Imperial Valley but is usually more prevalent in the coastal sec- 
 tions. Tipburn (actual cause unknown) occurs annually in most of 
 the important lettuce districts and is thought to be induced by certain 
 unfavorable climatic conditions. Slime (caused by Boirytis spp. and 
 certain bacteria) usually attacks plants previously injured by tipburn. 
 In addition to these four diseases, others of minor importance occur 
 annually but do not usually cause heavy losses. Drop (Sclerotinia 
 spp.), mosaic, and yellows have been found in California. Fortunately 
 for lettuce growers, brown blight and mildew are now under control 
 through the utilization of resistant strains, and some progress has 
 been made with tipburn. Strains which resist tipburn are not likely 
 to become slimy; hence slime control depends to a large extent upon 
 the success in breeding tipburn-resistant strains. 
 
 Brown Blight. — Lettuce brown blight is known to occur only in 
 California and Arizona. At present it is more prevalent in Imperial 
 Valley than in the Salinas-Watsonville or the Santa Maria sections, 
 but it is likely in time to become epidemic in the two latter districts 
 also. Although the cause is as yet unknown, the inducing agent has 
 been found able to persist in infested soil for long periods, even 
 though nonsusceptible crops are grown. Occasionally the first lettuce 
 crop on ''new" land is slightly attacked, the disease gradually becom- 
 ing more severe with succeeding lettuce crops (fig. 31). The disease 
 has been thought to develop more rapidly in fine, silty, water-deposited 
 soil types than in loamy soils. In some fields of the silt type in 
 Imperial Valley, brown blight has made it impossible to grow more 
 
1932] 
 
 The Head-Lettuce Industry of California 
 
 45 
 
 than one or two lettuce crops, while in the Salinas-Watsonville district, 
 five to ten profitable crops have been produced on loamy soils. 
 
 The disease may manifest itself at any time after the seedlings 
 have developed five leaves, usually after thinning. Plants attacked 
 when small assume a somewhat mottled, sickly yellow color, become 
 rosetted, and never head. If attacked after heading, the entire plant 
 may become yellowish ; and dead, brown irregular streaks and blotches 
 may develop in the outer leaves. Infected leaves usually dry up 
 and turn brown. 
 
 s«^ <i i k^l'^r^ 
 
 
 '^'^ 
 
 »«ww *.^^— ^ ^ '. -" I 
 
 Fig. 31. — Fields of lettuce showing increase in severity of brown blight as the 
 number of lettuce crops grown successively on the same land increases. The field 
 on the right shows from 75 to 100 per cent brown blight infection. Lettuce was 
 grown in this field the two preceding years. The field on the left shows from 20 
 to 40 per cent brown blight infection. This field produced a lettuce crop the 
 preceding year. (From Cir. 295.) 
 
 Although brown blight threatened to become so severe in Imperial 
 Valley that lettuce could no longer be profitably grown, the disease 
 is now under control through the efforts of Dr. Ivan C. Jagger of 
 the United States Department of Agriculture. Dr. Jagger began his 
 investigations in California in 1922 and has now distributed six 
 brown blight-resistant strains which succeed on infested soil where 
 other strains of New York are a total loss (fig. 32). The adaptability 
 and resistance of these six strains (Imperial Nos. 2, 3, 6, and Imperial 
 C, F, and D) are discussed elsewhere in this circular. 
 
46 
 
 California Agricultural Extension Service 
 
 [CiR. 60 
 
 Downy Mildew. — In the coastal sections downy mildew {Bremia 
 lactucae) is usually present every season; in Imperial Valley, only 
 during an occasional season when there is an unusual amount of rain 
 and dew. The disease also attacks endive, chicory, and certain weeds. 
 Plants may be attacked at any stao^e of development, depending on 
 certain environmental conditions, such as relatively low air tempera- 
 ture and periods of cloudy or rainy weather or heavy dews. Symptoms 
 are evident on the leaves or seed stalk. On the leaves, yellowish or 
 light green areas develop on the upper surface; the corresponding 
 lower surface is usually covered by a dense, white or greyish, fluffy 
 growth of the fungus which produces the spores capable^ of infecting 
 
 Fig. 32. — Comparison of brown blight-resistant and nonresistant lettuce. The 
 two center rows are 100 per cent infected. The outer rows of resistant strains 
 show normal growth. 
 
 other leaves. Infected spots may enlarge or several grow together 
 until much of the leaf may be killed. Under California conditions, 
 infected plants seldom die prematurely, but continue to grow more 
 or less salable heads. Irregular white blotches may appear on infected 
 seed stalks. When infected heads are shipped under refrigeration to 
 distant markets, decay may follow mildew injury. 
 
 The causal organism is able to persist in the soil for a short time 
 but will not withstand the freezing and thawing of winter in the 
 North. Wild lettuce serves as a host in the ''off season," enabling 
 the organism to live over until lettuce is again planted. How long the 
 organism is able to persist in the soil in either the Imperial Valley 
 or the coastal districts is not definitely known. 
 
 Preventive measures include destruction of wild lettuce and other 
 weed hosts and prompt removal or destruction of infected plants as 
 
1932] The Head-Lettuce Industry of California 47 
 
 soon as the cutting* season is over. Dr. Jagger has developed three 
 resistant strains, Imperial C, D, and P, through hybridization and 
 selection. In 1922 he crossed New York, a susceptible variety, with 
 a resistant French variety of Romaine. These hybrids were then 
 crossed with Imperial Nos. 2 and 3 in 1925, and continued selection 
 resulted in the isolation of strains C, D, and F, which are resistant 
 to both mildew and brown blight. These strains are further discussed 
 elsewhere in this circular. 
 
 Tiphurn. — Tipburn is a nonparasitic disease generally prevalent 
 when warm, bright days follow periods of foggy or cloudy weather. 
 It is characterized by dark brown discoloration near the margin of 
 the upper, more tender, exposed leaves. The development of these 
 small dead spots seems to prevent the passage of water to edges of 
 the leaf ; and that portion outside the spots becomes wilted and yellow 
 and soon dies, leaving a dead, brown strip around the edge of the leaf. 
 New York No. 12 is somewhat resistant, but not immune, to tipburn. 
 
 Slime. — Lettuce heads which have been subjected to tipburn in the 
 field often develop a slimy soft rot or grey mold in the field or during 
 transit and storage. This condition is caused by Botrytis and a number 
 of different bacteria. Heads subjected to frost injury often develop 
 slime. Infection usually starts on a protected, injured spot, from 
 which the causal organisms may spread by means of water, wind, or 
 insects to other plants. Sometimes the outer leaves tend to hide 
 infected areas within the head. If injured leaves at the base of the 
 plant are attacked, Botrijtis often enters the stem, causing a rot at 
 the soil surface ; and the plant wilts. 
 
 Slime develops most rapidly during warm, damp periods; its 
 development is checked by cold, dry weather. In the field, the control 
 of slime usually resolves itself into prevention of tipburn. Strains 
 resistant to tipburn are likewise less subject to slime. Where slime is 
 a serious factor, plantings should be regulated so that the crop will 
 mature in cool weather. Harvested heads showing any indication of 
 slime should not be packed for long distance shipment, as slime is 
 likely to spread during transit. 
 
 Yellows. — The nature and effects of lettuce yellows indicate that 
 it is potentially a serious disease, although it has not caused appre- 
 ciable loss in California to date. The disease is induced by a virus 
 that is spread from diseased to healthy plants by the six-spotted 
 leafhopper, Cicadula sexnotaia, an insect extensively distributed in 
 California. Infected leaves become yellowed and elongated ; and the 
 leaves of infected plants often turn outward instead of inward and 
 
48 California Agricultural Extension Service [C^R- ^^ 
 
 fail to head. Diseased plants had best be removed from the field and 
 destroyed. 
 
 Big-veined Lettuce. — This disease has been observed in the Im- 
 perial Valley for a, number of years. As the name indicates, the 
 veins become large and coarse. While the lettuce usually heads, it is 
 smaller than normal. Apparently this is a soil-borne disease as it 
 persists year after year in the same ground. The acreage affected as 
 yet is small, but is steadily increasing. The present strains of Imperial 
 are susceptible to this disease but selections are now being made by 
 Dr. Jagger for resistance. 
 
 Other Diseases. — Lettuce drop {Sclerotinia minor and 8. liher- 
 tiana), mosaic, and mottle leaf are known to occur in California but 
 do not yet rank as serious diseases. 
 
 SHOOTING TO SEED PREMATURELY 
 
 Some loss is always caused by plants going to seed prematurely. 
 This trouble usually results from unfavorable soil, moisture, and 
 climatic conditions. It is difficult to determine in all cases just what 
 the contributing factor or factors have been in bringing about this 
 condition. The best lettuce seed available should be purchased; but, 
 above all, growers should not attempt to grow lettuce under high 
 temperature conditions, on steep slopes, or on light sandy or gravelly 
 soils that are not retentive of moisture. 
 
 ACKNOWLEDGMENTS 
 
 The authors are indebted to the following men for help in the 
 preparation of this circular : T. I. Storer, F. H. Wymore, I. C. Jagger, 
 J. B. Scherrer, F. G. Beyschlag, W. 11. Nixon, F. 11. Ernst, D. R. 
 Porter, and Luther Sigmon. 
 
 15m-3,'32