LETTUCE October 1983 (New)
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Commercial Vegetable Recommendations Extension Bulletin E-1746, LETTUCE October 1983 (new) Bernard H. Zandstra, Department of not cover the heads well, leaving them peratures of 70° to 80° F. Tempera Horticulture; Darryl D. Warncke, subject to sun scald. Leaves are fre tures above 85°F result in sun scald Department of Crop and Soil quently quite ribby (i.e., very large (wrapper leaves break down and stick Sciences; Melvin L. Lacy, Depart midribs) which results in cracked to the head) and tipburn. Tempera ment of Botany and Plant Pathology midribs at harvest. Ithaca is very tures below 30° F will cause severe susceptible to brown rib. frost damage to the heads. Production Raleigh is a recently released varie ty that has done well in Michigan A good yield of head lettuce is 800 Water and Irrigation trials for 3 years. It produces large, 50-lb. boxes per acre; under ideal con firm, uniform heads with good flavor. Lettuce deteriorates rapidly under ditions, production can exceed 1,000 Large wrapper leaves give protection wet soil or very humid air conditions. boxes per acre. Other types of lettuce from sun scald. It has some tolerance Several foliar and root diseases thrive yield 600 to 800 25-lb. boxes per acre. to corky root rot. Ribs may become in a damp atmosphere. However, brittle and crack as heads become lettuce seeds need an adequate supply Use oversize. Because of its large size, of moisture to germinate uniformly, Raleigh may be a substitute for Ithaca. and the plants need a constant supply Approximately 80% of the head let Growers should try it on a trial basis of water throughout their growth and tuce grown in Michigan is packed in only. development to produce marketable cartons for the fresh market; 20% is heads. Balancing the need for mois shredded for use in restaurants. Montello, Green Lake, and Ithaca are also suitable for production on ture and the susceptibility to too Types and varieties mineral soil. much water is probably the most dif Butterhead: Bibb, Summer Bibb, ficult aspect of lettuce production in Several types of lettuce (Lactuca Buttercrunch, White Boston Michigan. sativa) are commonly grown commer Romaine: Parris Island, Lettuce seeds should be planted in cially: crisphead (iceberg), butterhead Valmaine, Rubra (red) moist soil. If the weather is hot at (bibb, Boston), romaine (cos), loose- seeding, irrigate with Vz inch of water Leaf: Domineer, Grand Rapids, leaf, and stem lettuce. Endive and immediately after seeding, and main Waldmann's Green escarole (Cichorium endivia) are close tain a moist soil surface until the ly related to lettuce and grow similar Stem lettuce: Celtuce seedlings emerge. ly in the field. Endive: Salad King, Green Curled After thinning", lettuce grown on The following crisphead varieties Escarole: Broad Batavian, Florida deep muck usually does not require are suitable for production on muck Deep Heart more irrigation before harvest. For soil: lettuce grown on lighter soils, and Montello forms uniform medium- Climatic Requirements during extended hot periods without large heads. Medium-size wrapper rain on muck soils, subsequent irriga leaves provide partial to good protec Lettuce requires a moderate climate tions may be needed. Irrigate with 1 tion for the head. The midribs are to grow well. It is sensitive to both inch of water every 10 to 14 days fairly smooth with little ribbiness, but high and low temperatures, and wet before heading and every 7 to 10 days they are quite subject to cracking. and dry conditions. Lettuce seed ger during heading. Irrigate in the morn Mature heads are firm with a light minates at temperatures as low as ing so that leaves dry out quickly. Be green basal color. Flavor is acceptable 40°F, but germinates best at 60° to conservative, and do not irrigate if to good. It has some tolerance to 70°. However, it is subject to thermo- rain is expected. corky root rot. dormancy at temperatures above Lettuce is often seeded on the outer Green Lake is a sister line of 80°F; i.e., the seed will not germinate, edges of raised beds, to avoid a Montello. The heads tend to be slight or will germinate erratically. saturated root zone in case of heavy ly larger but less firm than Montello. Lettuce grows best in sunny, dry rain or rain following irrigation. This Wrapper leaves provide good cover weather, with daytime high tem planting system also allows for better over the head. Flavor, midrib char acteristics, basal color and tolerance to corky root rot are similar to The authors acknowledge the help of Robert E. Lucas, Department of Crop and Montello. Soil Sciences (retired) and Edward J. Grafius, Department of Entomology, in Ithaca forms large firm heads with preparing this publication. good flavor. The wrapper leaves do Cooperative Extension Service • Michigan State University air circulation around the base of the symptoms disappear. On new mucks hand, using a small hoe or com plants, which helps avoid foliar testing below 20 ppm copper (Cu), parable tool. At 18 inches between diseases and bottom rot. apply 3 to 5 lb. copper per acre (12 to rows and 12 inches between plants, 20 lb. copper sulfate) in the broadcast there is a potential for 29,000 plants or Soil Requirements fertilizer each year until a total of 30 about 1,200 cartons of head lettuce to 40 lb. total copper has been applied. per acre. Lettuce grows well on both well- Cu deficiency should not subsequent Sow seeds V* to Vi inch deep into drained muck and mineral soils. It is ly be a problem. moist soil. During hot, sunny weather, usually grown on muck in Michigan Lettuce is susceptible to tipburn (see sow in the late afternoon or evening because muck maintains uniform below). To help avoid tipburn, spray so that seeds germinate before moisture levels better than mineral lettuce plants twice weekly during hot thermodormancy sets in. soil. Heavy soils hold moisture too weather with 10 lb. calcium chloride Sowing begins as soon as fields can long and result in root and bottom or 15 lb. calcium nitrate in 50 to 100 be worked in the spring. Plant twice a rots. gallons of water per acre. Direct the week until May 10 and 3 times a week Lettuce should be rotated with other spray into the center of the plant. thereafter until August 1. At each crops to avoid a buildup of soil-borne Once heads form, this will not help. date, plant an area of land that will diseases. Leafy type lettuce and endive and provide enough lettuce for 2 days of escarole are more susceptible to tip- harvest. After sowing, irrigate with Vi Fertilization burn than are heading types, and inch of water, unless soil is uniformly calcium sprays will be more effective moist. An 800-box per acre crop of head on them. lettuce uses approximately 125 lb. N, Harvest and Post Harvest 50 lb. P20B, and 200 lb. K20 from the soil. To maintain soil nutrient levels, Spacing and planting Head lettuce takes 55 to 75 days add 100 lb. N, 75 lb. P205, and 200 lb. from sowing to maturity, depending K20 per crop. On muck soil, maintain Land to be planted to lettuce should on temperatures. Lettuce sown in a pH of 5.2-6.0. On mineral soils, be plowed shortly before planting, to April matures in about 75 days; May maintain a pH of 6.0-6.8. a depth of 8 to 10 inches. Plowing too or August—70 days; July—60 to 65 Phosphorus and potassium ferti early results in loss of soil moisture. days; June—55 to 60 days. lizer rates should be based on soil test Plow deep enough to turn all trash Lettuce is cut and packed in the results. The following recommenda completely under. Disc or roll the field. If possible, harvest in the morn tions can be followed if a soil test is land to make a firm, smooth seedbed ing to avoid field heat. Head lettuce is not available. and sow immediately. If planting on packed 18 or 24 heads to a 1% bushel To prepare muck soil for planting beds, form the beds and sow in the carton, weighing about 50 lb. full. A lettuce, broadcast 300 lb. 0-0-60 (180 same operation or the same day. field is mature when most of the lb. K20); band at seeding (2 inches to Plant head lettuce in rows 15 to 18 heads have reached desirable size and the side and 2 inches below the seed) inches apart, with 12 to 14 inches be are solid. Most commercial fields are 300 lb. 8-32-16 and 25 lb. manganese tween plants in the row. Large-headed harvested only once. sulfate (24 lb. N, 96 lb. P205, 48 lb. varieties, such as Ithaca, need the To maintain quality, lettuce should K20, 6 lb. Mn). At thinning, sidedress wider spacing. Leaf lettuce may be be vacuum cooled for 30 minutes. If with 50 lb. N. An alternative method planted 6 to 10 inches apart. It takes % lettuce is dry, it should be sprinkled is to broadcast 1,000 lb. 5-20-20 before to Vz lb. of seed to plant an acre of with water before vacuum cooling. It planting, sidedress with 50 lb. N after lettuce. Planters that drop 3 to 4 seeds can be stored for 2 to 3 weeks at 32 to thinning, and apply manganese as per hill use about % lb. of seed per 34°F and 95% R.H. (relative humid foliar spray. acre in 18 inch rows with 12 inches ity).