Salad Crops & Greens Crops (“Leafy”) • Lettuce Lettuce – Lactuca sativa • Spinach • Family: Compositae – Spinacia oleracea • Self-pollinated annual (all varieties are self- • New Zealand Spinach pollinated inbreds, “OP”) – Tetragonia tetragoniodes • Collards & Kale • Generally considered a cool season crop o o o – Brassica oleracea Acephala group •<85F Optimum: 70 F day, 50 F night • Mustard Greens • Cultivated Types: – Brassica juncea, other Brassica sp. – Crisphead/Iceberg (L. sativa var. capitata) • Turnip Greens – Butterhead/Boston/Bibb (L. sativa var. capitata) – Brassica rapa Rapifera group – Cos/Romaine (L. sativa var. longifolia) • Swiss Chard – Looseleaf/Leaf (L. sativa var crispa) – Beta vulgaris Cicla group – Batavia – Intermediate between crisphead and • Endive, Escarole, Arugula, Cilantro, butterhead (‘loose-head’) Radicchio, Dandelions, Chicory, Parsley Crisphead Butterhead • Most popular type in • Semi-heading • Veins, midrib and stem the US not as prominent as in • Tolerate shipping crisphead types and handling better • Considered better quality than crisphead than other types • Susceptible to bruising • California & Arizona and tearing produce most of the lettuce in US • ‘Boston’ type larger and lighter green than ‘Bibb’ type Cos - Romaine Looseleaf – Leaf - Bunching • Long narrow leaves, • Forms rosette of leaves, upright growth and not a head loose head • Variable color, texture • More tolerant of and shape extreme weather • Generally more tolerant conditions than of environmental extremes crisphead or than any of the heading types butterhead – easiest to grow • Not as tolerant to • Leaves bruise easily and has short shelf-life – not shipping/handling as crisphead, but better than butterhead adapted for long-distance shipping 1 Plant Growth & Development - Plant Growth & Development - Seed Seed • Seed is a dried fruit (achene) • Visible light required for germination – Outer layer is the pericarp (ovary wall) surrounding – Degree dependant on genetics the seed coat, endosperm and embryo – At maturity, the endosperm is gen. used up – Phytochrome in the embryo can be converted to germination promoter (under visible light) or • Lettuce seed usually has dormancy (up to to germination inhibitor (under far-red several months, determined by genetics) wavelengths) – reversible process • Germination can be inhibited by high temperatures • Chemicals (plant hormones) are – Degree dependant on genetics sometimes used to treat seed to overcome – Related to seed coat or endosperm high temperature and light requirements to • When removed there is no inhibition avoid induced dormancy problems Plant Growth & Development - Plant Growth & Development - Vegetative Reproductive • Lettuce growth rates greatly influenced by • Lettuce is a “long-day” plant temperature – Photoperiod >12 hour of light required for – High temperatures = faster growth rates flowering (exact duration determined by – High temperatures = bitterness genetics) • If heading is initiated prematurely because • Premature flower initiation (bolting) can of high temperatures, smaller head sizes happen under high temperatures and long and poor quality will result days: – Genetics have influenced this for fall – Plants reach vegetative maturity quickly production in Arizona because of high temperatures, and flower because of long days Crop Establishment Crop Establishment • Primary method: Direct • Direct seeded fields seeding are overhead irrigated – Requires thinning, although to maximize soil precision planting with contact of shallow pelleted seed is reducing the need planted seed and initiate germination • Transplants used in areas where optimal growing season is short (usually due to high temperatures) 2 Crop Establishment Crop Establishment - Spacing • Plant spacing is critical for optimum yields of quality produce • Once crop is • Crispheads are typically spaced at established, furrow exactly 11” by commercial irrigation is the most growers today, but genetics play common practice an important role – Close spacing delays maturity but reduces chances of premature bolting – Doubles may not head at all • Optimum yields of the other types typically occurs with closer spacing Weed Control Diseases • Weed removal critical for quality crop • Lettuce Drop • Only effective chemical controls are pre- – Sclerotinia sclerotiorum plant herbicides (must apply before • Wide spread disease planting) organism • Hand-weeding still sometimes practiced, • Creates survival but very expensive (>$100/acre, structures (sclerotia) depending on weed pressure) that can survive for a long time under adverse conditions Diseases Diseases • Lettuce Big Vein Virus • Lettuce Mosaic Virus – Virus transmitted by – Transmitted by aphids, but primary inoculum soil fungus is infected seeds – Seed companies go to great lengths to produce LMV-Free seed • Grow seed crop in isolation where LMV is currently not found, being certain to use LMV-free seed 3 Physiological Disorders Harvest & Postharvest Handling •Tipburn • Hand harvested and field – Brown spots along the packed outer margens • Usually once-over harvest – Related to calcium (like • Commercial crop vacuum blossom end rot), because cooled to 32-34oF and high calcium in leaves is humidity abnormally low, even though • Shelf-life of crisphead types is soil levels may be high 3-4 weeks @ 32oF •Premature bolting •At 37oF, shelf-life decreases – Factors previously approximately 50% o mentioned • Freezing injury occurs at 31.7 F – Just the initiation of flowering can reduce quality • Looseleaf types respire at about twice the rate of heading types, so shelf-life is reduced proportionately – Genetics can play a strong role • Sensitive to ethylene – Exposure causes russet spotting Mesclun Mix Greens Leafy Vegetable Greens • Blend of greens • Other than Lettuce combined for their • Most are cool season crops variety of textures, flavors and colors – Best quality when grown in cool environment grown and sold – Exceptions: together • New Zealand Spinach (warm season) • May include • Swiss Chard: cool season, but doesn’t loose various types of quality as much in warmer environment lettuces with other types of greens Spinach Crop Establishment • Spinacia oleracea - Chenopodiaceae family • Center of Origin: Central Asia • All commercial production is direct seeded • The only commercially important Leafy Vegetable Green in the field • Dioecious – Two types of males: vegetative males & extreme males • Seed germinates at relatively low o • Extreme males are small plants that flower quickly temperatures. Optimum: 45-75 F • Vegetative males and females are more productive • Breeding has eliminated extreme male genetics from current • Fresh market crop is sometimes thinned varieties • Cool season annual • Processing crop is planted to stand, often – Temperatures as low as 20oF, but optimum = 60o-65oF drilled in rows 5 – 20 inches apart – Flowers in response to temperature (cool→warm, but not considered a biennial) & photoperiod (long-day: 12-15 hour • Typical plant spacing is 3” depending on genetics) – Too close and the stems grow too long 4 Weed Control Spinach Types • Much of crop is machine harvested, so weed control is critical – No one wants weed in their canned spinach! • No good chemical for broadleaf weeds, so cultivation has been the norm – But because spinach is a “quick” crop (40-50 days), using a clean field with grass herbicides and one cultivation is usually Smooth Leaf effective Savoy Leaf Processed Fresh Harvesting Postharvest • Ready for harvest when big enough to eat • Highly perishable – “baby” spinach – Shelf-life 10-14 days at 32oF and 95-100% • Processing crop tends to be harvested at maximum size, RH before yellowing or deterioration • Controlled atmospheres of 10-40% CO2 • Multiple harvest possible even and 10% O reduce yellowing and improve with machine harvest 2 • Must be harvested prior to quality bolting – loss in quality • Long-standing cultivars: resist • Usually packed in bags to maintain bolting, and “stand” in the field for a longer period of time environment and prevent wilting New Zealand Spinach Crucifer Crops as Greens • Not a true “Spinach” • Tetragonia tetragoniodes • Looks like spinach, consumed like spinach, but much more heat tolerant, not very frost tolerant • Large spreading plant 3-4’ across, 1-2’ tall • Require wide spacing between plants (12- 24” plant spacing, 36” row spacing) 5 Collards & Kale • Brassica oleracea Acephala group • Non-heading cabbage – Collards have smooth leaves – Kale has curled, savoy leaves • Collards in particular are much more tolerant of temperature extremes than cabbage (esp. warmer temperatures), but still do best as a cool season crop. • Both are biennials • Multiple harvests are made by cutting single leaves without damaging the growing point Mustard Greens Mustard Greens • May be multiple Brassica • Leaf mustard (B. juncea) species, but leaf mustard AKA India mustard – Get’s spicy hot if grown is B. juncea under stress or in hot • Spinach mustard is B. weather – Taste is milder after rapa (Perviridis group) cooking • Resemble spinach in • Spinach mustard (B. growth habit and culture rapa) accumulates less spice under warm • All are members of conditions Crucifereae, and are cool • Both are susceptible to season biennials (or bolting, especially in pseudo-biennials) spring (warm weather following cool periods) Turnip Greens Pests • Brassica rapa Rapifera • Same as for other Crucifer crops group • Worms & other leaf eaters – Same as Turnip grown for roots – Some cultivars don’t