A3788

K.A. DelahautA.C. Newenhouse

Growingsalad greensin WisconsinA guide for fresh-market growers

ContentsPlant description, 1

Site selection, 3

Cultivar selection, 4

Planting, transplanting, and culture, 6

Season extenders, 11

Soils and nutrient management, 12

Irrigation, 13

Harvest, handling, and storage, 14

Insect management, 16

Disease management, 19

Weed management, 22

Additional reading, 23

Successful fresh-market gardening involves

more than just a talent for growing high-quality

vegetables. You also need to find a market for

them. Before you start, visit other growers,

develop a marketing plan, and evaluate the

feasibility of your proposed business. Think

about what is unique about your product. Are

you promoting the product for taste, freshness,

health benefits, value-added, or time of avail-

ability? For assistance determining your

market, consult with your county Extension

agent or refer to Extension publication Direct

Marketing of Farm Produce and Home Goods

(A3602).

�

1p

lant descrip

tion

Salad greens provide market gardeners a highvalue crop that brings a premium price if grownand marketed successfully. Salad mixes have

become particularly popular among customersseeking convenience. Salad mix is a collection ofleafy greens pre-mixed and sold together. This ideaoriginated in France centuries ago where a mix ofimmature “baby” greens was called “mesclun.” Thegreens can be grown as a mixture in the field orcombined after harvest.

Because of their highly perishable nature, saladgreens are better suited to local production than longdistance shipping. Growers should be aware that theinputs necessary to produce a quality crop can behigh and include a lot of hand labor.

The crops discussed in this publication include fourtypes of lettuce (crisphead, butterhead, romaine, andleaf), spinach, endive, escarole, radicchio, witloof,and Swiss chard.

Plant descriptionMost of the salad greens grown in Wisconsin belongto one of three plant families: Asteraceae (compositefamily), Brassicaceae (mustard family), orChenopodiaceae (goosefoot family). The majority arecool-season annuals, although some varieties cantolerate summer heat. As a result of the naturalgrowing conditions suited for salad greens, somemarket gardeners only offer them early in the seasonand again in the fall when temperatures cool down.

LettuceLettuce (Lactuca sativa) is a cool-season, herba-ceous annual in the Asteraceae family, native to theeastern Mediterranean and Asia Minor. Early recordsof lettuce cultivation have been found on Egyptiantombs dating back to 4500 B.C. Lettuce was culti-vated for the medicinal properties of its milky sapand for its seed oil. Lettuce is thought to have arisenfrom Lactuca serriola, a widely dispersed, primitive,spiny form. The word “lettuce” is derived from lactis(Latin for “milk of plants”). Despite the low level ofvitamins and nutrients in most lettuce varieties,lettuce is considered the fourth most significant U.S.crop from a nutritional standpoint because of thelarge volume consumed. Lettuce contains fiber,vitamins A and C, calcium, and iron. Leaf lettuce hasmore nutritional value than head lettuce, and darkgreen leaves have more nutritional value than lightcolored leaves.

The different varieties of lettuce have a huge variationin leaf shape, texture, color, and overall plant form.

2SpinachSpinach (Spinacia oleracea) originated near Iran andwas introduced into China via Nepal in 647 A.D., andinto Spain via N. Africa in 1100 A.D. Spinach is amember of the goosefoot family, Chenopodiaceae.The genus name Spinacia refers to the prickly seedcapsule and is derived from spina which means“spiny” in Latin. This hardy, cool-season annual is animportant source of vitamins A and C as well ascalcium, phosphorus, iron, and potassium. Spinachis also high in fiber and relatively high in protein.Spinach leaves are borne in a rosette with manyleaves attached to a short fleshy stem. Leaves maybe smooth or savoy (crinkled). Savoy types have alayer of cells that continue to grow between the leafveins causing a puckering effect. Spinach cultivarsmay be upright or spreading.

Endive and escaroleEndive (Cichorium endivia) is a hardy annual orbiennial with two forms: curly and broadleaved.Endive is a member of the composite family,Asteraceae. Records of its cultivation date back toancient Egypt. Curly endive is also known aschicorée or frisée and has narrow, lacy, deeply cutcurly leaves. Broadleaved endive is called escaroleand has large, crumpled, smooth-edged leaves. Bothcurly endive and escarole have a slightly bitter taste,although much less so than radicchio. Curly endivewithstands heat better than escarole, radicchio, andwitloof. Escarole is more cold tolerant than witloof orcurly endive and also tolerates low light conditions,making it potentially well-suited for winter greenhouseproduction.

Radicchio and witloofRadicchio (Cichorium intybus) is native to theMediterranean region and is a cultivar of chicory.Radicchio forms loose, small heads similar to apointed cabbage. It typically has red leaves that arewhite along the midrib and near the base. The bitterleaves sweeten slightly in cooler weather. Radicchiois somewhat frost tolerant.

Witloof (Cichorium intybus) is closely related to radic-chio and is a common European salad crop that canbe grown in the Midwest. It is also sometimesreferred to as Belgian endive or chicon. Witloof isFlemish for “white-leaf.” It does not form heads butproduces a tight cluster of individual upright leaves inthe second year of growth. Plants are grown in thedark to blanch the leaves so they’ll remain tender andless bitter. Witloof is eaten raw in salads and alsosteamed, boiled, or baked. Witloof is very perishableand does not ship easily. Since it is not commonlygrown in Wisconsin, you may need to test your poten-tial market before you plant a lot of it. Try forcing afew roots on a small scale, eating them yourself soyou can describe the flavor, and then visiting poten-tial customers with your sample product. Witloof doesnot contain many vitamins or nutrients.

Swiss chardNative to the Mediterranean region, Swiss chard(Beta vulgaris var. cicla) is a member of theChenopodiaceae family and technically a variety ofbeet (Beta vulgaris). Swiss chard is grown for itslarge crinkled edible leaves and fleshy leaf stalks(petioles) which taste similar to spinach. It is anherbaceous biennial which is grown as an annual.Unlike most other salad greens, chard does not bolt(form a premature seed stalk) when exposed to hightemperatures. Therefore, chard is often grown duringthe heat of summer.

3Site selectionBecause salad greens are planted early in thespring—in most cases as soon as the ground can beworked, it is important to select a site where the soilwarms rapidly. Salad greens transpire a lot of waterand also have shallow root systems, so soil withgood moisture retention is beneficial for these crops.Adequate drainage helps prevent diseases. Earlyseason crops are often planted on sandy soils whichwarm up quickly and can be worked early. Mid- tolate-season crops should be planted on heavier soilsor soils with a high organic matter content so theyhave better moisture-holding capacity. Growing leafycrops on muck soils reduces the amount of gritcaught in crinkled leaves such as those of spinach.Salad greens respond well to rich, friable soil high inorganic matter. Small seeds common to salad greenscannot germinate in crusted soil.

Salad greens are especially attractive to deer.Consider using portable electric fencing to protectyour crop. Consult your county Extension office forinformation.

site selection

Specialty greens Numerous crops are grown as salad greens in theMidwest. Some, such as arugula, mizuna, and dan-delion, are used in small quantities to add flavor tosalad mix. Others, such as New Zealand spinachand purslane, grow well in hot weather and are usedto fill out summer salads, while cold-tolerant cropssuch as mâche, claytonia, and cress extend thegrowing season. For more information about thesecrops, consult the resources list at the end of thispublication.

Common name(s) Scientific name

amaranth Amaranthus tricolor

arugula Eruca sativa

cilantro Coriandrum sativum

collards Brassica oleracea

corn salad, lamb’s Valerianella locustalettuce, mâche

cress Lepidium sativum

dandelion Taraxacum officinale

kale Brassica oleracea andBrassica napus pabularia

miner’s lettuce, winter Claytonia perfoliata or purslane, claytonia Montia perfoliata

mizuna Brassica rapa var. japonica

mustard Brassica juncea

New Zealand Tetragonia spinach tetragonioides

orache Atriplex hortensis

purslane Portulaca oleracea

sorrel Rumex acetosa

tat soi Brassica rapa var. narinosa

Cultivar selectionThere are four main types of lettuce commonly grownin the Midwest: crisphead, butterhead, romaine, andleaf. Lettuce is bred for disease resistance, leaf orhead color, size, shape, texture, flavor, earliness, uni-formity, and heat tolerance (resistance to bolting).Some varieties of lettuce perform better under longday conditions while others are day-neutral and notaffected by day length. Table 1 lists some recom-mended cultivars for Wisconsin.

Crisphead lettuce cultivars (Lactuca sativa var.capitata) are often synonymous with “iceberg”lettuce, which is the name of a cultivar. Leaves arelarge, heavy, and brittle. The outer leaves are greenwhile the interior leaves are white or yellow. Afterinitial rosette development, leaves begin to overlapeach other and become tightly folded to form adense head which is usually more than 6 inches indiameter.

Butterhead lettuce cultivars also belong to L. sativavar. capitata, but the heads are smaller and morecompact, the leaves are loosely crumpled and haveless prominent veins and midribs, and the lettucehas more flavor and a buttery texture compared tocrisphead lettuce. There are two distinct types of but-terhead lettuce: Boston—a day-neutral cultivar whichproduces large heads with light green leaves, andbibb—a smaller, dark green, short-day cultivar. Bibblettuces do not travel well since their leaves bruiseand tear easily, so these types are well suited to localproduction. A third type, Batavia, has characteristicsthat are intermediate between Boston and bibb.

Romaine, also known as cos (Lactuca sativa var.longifolia), produces elongated upright heads withlong leaves that have prominent midribs. Romainelettuce has coarse outer leaves and tender, flavorfulinner leaves. It is more tolerant of adverse environ-mental conditions such as temperature and moistureextremes than crisphead and butterhead lettuce.

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Note: Cultivars of saladgreens perform verydifferently dependingon soil temperature, airtemperature, and daylength. Choose culti-vars according to yourown situation andneeds. Consider whatyour market demands,the length of yourgrowing season, yoursoil, pests, diseases,irrigation, cultivars othergrowers like, and culti-vars you personallylike. When trying a newcultivar, do not use itexclusively. Grow newtrials next to oldstandbys so you maycompare the character-istics objectively.

Crisphead

Cardinale

Crispino

Great Lakes

Ithaca

Loma

Nevada

Rosa

Sierra

Summertime

Butterhead

Buttercrunch

Ermosa

Esmeralda

Four Seasons

Little Gem

Nancy

North Pole

Pirat

Summer Bibb

Winter Marvel

Romaine

Athena

Cimmeron

Deer Tongue*

Freckles

Giant Caesar

Kalura

Little Caesar

Parris Island

Rouge d’Hiver

Rosalita

Rubens

Winter Density

Leaf

Black-seededSimpson

Brunia

Curly Oakleaf

Grand Rapids

Great Lakes

Green Ice

Ibis

Lollo Rossa

Merlot

Oakleaf

Prizehead

Red Sails

Royal Oakleaf

Salad Bowl

Simpson Elite

Slobolt

Sunset

Two Star

Waldmann’s

Table 1a. Recommended lettuce cultivars for Wisconsin

*Sometimes classified as butterhead.

5Leaf lettuce (Lactuca sativa var. crispa) cultivarscome in all types of shapes, colors, and textures.They are particularly well suited to local productionsince they do not ship well and would otherwise notbe available commercially from other states. Whenselecting cultivars for salad mix, keep in mind thatfrequent dense plantings are required, so you willneed a lot of seed. Since seed prices vary, you maywish to grow the more expensive varieties for matureheads or leaves and use less-expensive varieties forsalad mix.

Spinach cultivars are selected for their vigor, unifor-mity, disease resistance, nutrition, and resistance tobolting. Varieties are classified based on leaf texture:smooth or savoy (crinkled).

Endive, escarole, radicchio, and witloof cultivars arebred for less bitterness, resistance to tipburn, unifor-mity, nutrition, vigor, and appealing colors or leaftextures.

Swiss chard cultivars are bred for flavor, diseaseresistance, vigor, and color such as red, pink,orange, white, and yellow.

cultivar selection

Spinach

Avon (savoy)

Baby Leaf

Giant Nobel

BloomsdaleLong-Standing(savoy)

Melody (savoy)

New Zealand

Olympia

Space

Tyee

Viroflay

Whale

Radicchio

Adria

Carmen

Chioggia

Early TrevisoFirebird

Grumolo

Inferno

Palla Rossa

Red Surprise

Red Treviso

Rossana

Endive

Bianca Riccia

Frizz E

Full Heart

Neos

Salad King

Totem

Très Fine

Escarole

Coral

Full Heart

Nataly

Sugarloaf

Chard

Bright Lights(multi-color)

Charlotte

Fordhook Giant

Large WhiteRibbed

Lucullus

Monstruoso(white)

Rainbow

Rhubarb (red)

Ruby Red (red)

Vulcan (red)

Table 1b. Other recommended cultivars for Wisconsin

Long-day vs. short-day cultivarsSome cultivars require long days toinitiate flowering (at least 15 hours oflight) while others require short days(less than 12–15 hours). “Short day” isactually a misnomer as darkness ratherthan day length triggers blooms. Plantsthat are unaffected by day length areknown as day neutral.

Planting, transplanting,and cultureRefer to table 2 for the estimated amount of seedrequired, seed planting depth, yield, planting date,spacing, and days to first harvest.

Salad greens produce a marketable crop relativelyquickly and are typically planted in succession sothat growers can offer customers salad cropsthroughout the season. Sow seed as soon aspossible in the spring. (Figure 1 shows approximatedates of the last spring and first fall killing frosts ofthe growing season.) To help keep track of plantingsduring the hectic growing season, take some time inthe winter to make a calendar that lists proposedyearlong planting dates. Keep in mind that thenumber of days to harvest for fall crops may actuallybe longer than that listed on the seed packagebecause environmental conditions may slow growth.Some crops such as spinach can be overwintered, orgrown under shelter such as under floating rowcovers, in a cold frame, or in a tunnel or hoophousewith one to two layers of clear plastic. Escarole andsome other specialty crops such as claytonia,mâche, and land cress may also be grown underwinter protection.

If you grow heat-sensitive leafy crops in the summer,you can try to create a cooler microclimate byshading plants with a lightweight shade cloth, whichallows some light to pass through, or by plantingbetween rows of taller crops oriented in a north tosouth direction. Since high soil temperatures canprevent germination, you may wish to pre-germinateseed for late-summer plantings by soaking them inwater until the first root (radicle) just begins toemerge. Such seed needs to be planted by hand.

Soil preparationWork beds 6–7 inches deep to promote good rooting.Just before seeding, use shallow cultivation toprevent soil crusting. For early season crops on siteswhere erosion is negligible, prepare the site the fallbefore planting. Preparing the soil in the fall willprevent any planting delays caused by cold, wetsoils and will help reduce soil compaction associatedwith working wet soils. Compacted soils restrict rootgrowth, reduce the amount of oxygen available toroots, and limit water penetration, all of which canhurt yield potential.

Raised bedsRaised beds are an alternative to the conventionalfield planting method. They improve soil drainageand allow access to the crop without causing soilcompaction. Raised beds are typically 4–5 feet wideand 100 feet long. The width is determined by thetype of equipment used and by the crop. Leave a1-foot aisle on either side of each bed to accommo-date foot traffic.

SeedingSeeds for salad crops tend to be very small. Somecompanies offer pelleted seeds that are coated androlled to make them uniform and easier to handle,especially in precision seeders. Some pelleted seedsinclude pesticides in the coating. Precision seedingrequires specialized planters and uniformly sizedseeds, and prevents the need for thinning.Specialized planters include the gravity-feed coneseeder, the belt-drive seeder, and the vacuumseeder. Walk-behind plate-type seeders are alsoused. Some growers who do not use precisionseeders thin salad greens by hand and sell the thin-nings. Prevent a crust with shallow cultivation, mulch,or by supplying enough moisture to wet the soil atgermination but not to saturate it.

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7Starting seedsSalad greens can be started in the greenhouse andtransplanted outdoors to get a head start on thegrowing season. Start your transplants 3–4 weeksbefore you plant them outdoors. You can buy or mixyour own sterile potting mix for starting transplants.The mix should include peat, sphagnum, or compostto retain moisture; vermiculite or perlite for aeration;and mineral and nutrient sources to encouragegrowth after the first roots form.

Fill plastic or polystyrene cell trays with potting mix,or make individual blocks with a soil blocker. Cells assmall as 1 inch in diameter are fine. Plant seeds andcover with a fine layer of media. Label transplanttrays with cultivar and planting date. Keep mediamoist but not wet. Refer to the culture section to findthe best temperature for germination. Typically thenighttime temperature should be 10–15°F cooler.Thin seedlings to one plant per cell or plug, or oneplant per inch if grown in undivided flats. Ten daysbefore transplanting, move plants into a cold frame toharden them off, or put them outside for a few hourseach day during the warmest time of the day.

planting

, transplanting

, and culture

Last spring killing frost First fall killing frost

Figure 1. Approximate dates for first and last killing frosts

May 31–June 6

May 24–30

May 17– 23

May 10–16

May 3–9

April 26–May 2

September 13–19

September 20–26

September 27–October 3

October 4–10

October 11–17

October 18–24

8Table 2. Planting guide

Lettuce, Lettuce, Spinach Radicchio Endive and Swiss chard head leaf escarole

Planting datesa

(southern Wis.)

Indoors for transplanting March 15 variesb variesb March 20 variesb March 20

First outdoor May 1 April 15 April 15 May 20, April 15 April 15 planting also July 15

Frequency Every Every Every Everyfor salad mix — 2–3 weeks 2–3 weeks — 2–3 weeks 4 weeks

Planting notes Choose heat- Needs short Try different Tolerates Plant until tolerant days. Grows varieties higher temps 60 days varieties best at 55– for your than lettuce, before frost for summer. 65°F. Can growing but choose for mature Seed won’t . tolerate some conditions. heat-tolerant leaves and 30germinate frost, may and day length days before at soil temp overwinter. adaptable frost for >75°F. varieties for salad mix.

summer.

Plants or seeds/100 ft of row 120–150 plants 1⁄4 oz 1⁄2–1 oz 1⁄10 oz 1⁄8 oz 1⁄4 oz

Seed depth 1⁄8 1⁄8 1⁄2–3⁄4 1⁄4 1⁄4 1⁄2(inches)

Spacingc

Between plants 8 inches 1 inch apart Mature plants: 8–10 inches Mature plants: Mature plants: in single row 11⁄4 inch 8 inches 8–12 inches or in narrow Salad mix: Salad mix: Salad mix: beds (2–4 3⁄4 inch apart 1 inch apart 1 inch apartinches wide) in single rows in single row in single row

or in narrow or in narrow or in narrow beds (2–4 beds (2–4 beds (2–4 inches wide) inches wide) inches wide)

Between rows 12–18 inches 12–18 inches, 12–18 inches, 18 inches 12–18 inches, 12–18 inches,or in beds or in beds or in beds or in beds 4 feet apart 4 feet apart 4 feet apart 4 feet apart

Approximate Crisphead: Butterhead: Mature plants: 60–90 days Mature plants: Mature plants: days to first 60–120 days 21 days 35–50 days 52–90 days 50–60 daysharvestd Butterhead: Romaine: Salad mix: Salad mix: Salad mix:

42–70 days 29 days 25 days 31 days 29 days Romaine: Leaf: 50–70 days 27 days

aPlant about 1 week later along the lower lake shore and in the central part of the state and about 2 weeks later in northerncounties.

bCan be started indoors approximately 3–4 weeks before transplanting outdoors. You’ll need to experiment to find the beststarting time for your growing conditions.

cIf using a plate-type seeder, spacing between plants will be determined by the plate configuration.dCultivars will vary in time needed to reach harvest stage; extend the harvest season by planting cultivars of different maturitydates or by making successive plantings of the same cultivar.

9p

lanting, transp

lanting, and

culture

Lettuce cultureLettuce prefers temperature of 65–70°F during theday and 45–55°F at night. High light intensity andlong days increase the growth rate and hasten leafdevelopment. However, long days associated withhigh temperatures will cause lettuce to bolt. Lettuce,like most salad greens, can be planted out as earlyas April 15 in southern Wisconsin with successiveplantings made every 2–3 weeks to assure a continu-ous crop as long as cool weather permits. Someheat-tolerant varieties of lettuce can be planted aslate as early July. Under optimum conditions, lettuceseed will germinate in 2–4 days and emerge shortlythereafter. Cooler soil temperatures will slow the rateof germination, and germination stops at tempera-tures above 77–86°F (depending on cultivar). Forhead lettuce, plant three seeds every 8 inches inrows 12–18 inches apart and thin to one plant every8 inches. For leaf lettuce, plant densely and thin to 1inch between plants. Plant in rows 2–4 inches wideor in beds.

Decide whether you would like to combine seeds tomix cultivars within the planting beds or grow themseparately to be mixed postharvest. An advantage toplanting individual rows to only one cultivar is that ifdiseases or insects affect one type of lettuce, thenyou can more easily manage the problem than if theyare all grown together.

Light is required for germination so lettuce seed istypically only lightly covered with soil after planting.Sprinkle lightly for even moisture.

Head lettuce may be started from seed indoors andtransplanted out in early May to ensure adequatetime for maturity before high temperatures causeplants to bolt. Transplants can be planted in a honey-comb fashion in the field whereby alternating rows of3 plants and 2 plants equidistant from each other areplanted in the bed to maximize the use of availablespace. Transplants should be watered well at thetime of planting.

Spinach cultureSpinach leaves grow best at 55–65°F. Under longdays and warm temperature, spinach quickly boltsand stops producing large leaves. In the Midwest,spinach must be grown in the spring or fall whenshort days trigger leaf production instead of flowering.Plant spinach from mid-April through early May andagain from early August through early September. Atcolder temperatures growth is slowed. Spinach isvery hardy and if the plant is acclimated to cold it canwithstand some freezing down to 14–20°F. Spinachseeds can be sown in late fall the year before and,depending on temperature, they will grow to maturitybefore frost or grow to a size (3–4 inches diameter)that will survive the winter and begin growing newleaves early the next spring. Spinach seeds can alsobe sown in late fall or early winter and covered inmulch to sprout early the next spring.

Similar to lettuce, spinach is direct seeded in rows ormay be broadcast in beds. For salad mix, sow seeds3⁄4 inch apart in rows 2–4 inches wide and thin to 1inch between plants. Clip when small. For full-sizedleaves, plant 11⁄4 inches apart in rows 12–18 inchesapart and thin to one plant every 6–8 inches. Seedshould be planted 1⁄2–3⁄4 inch deep. Unlike lettuce,spinach is slow to emerge and temperature affectsthe percentage of seeds that germinate. In tempera-tures of 40–45°F, almost all of the seeds will germi-nate, but they will take up to 3 weeks to emerge. Inwarmer temperatures, germination is faster (7–10days) but fewer seeds will germinate.

Radicchio culturePlant radicchio by seed or from transplants in lateMay or early June, and seed a fall crop in mid-July.Plant three seeds 1⁄4-inch deep every 8 inches inrows 18 inches apart, and thin to one plant every8–10 inches. Harvest small heads in 9–10 weeks.Some growers cut back plants in late summer and letthem resprout, forming heads 4–6 weeks later.

10Witloof cultureWitloof, or Belgian endive, is direct seeded outdoorsin late June in rows 18–24 inches apart. Plantsshould be thinned to 6–8 inches apart within the row.In the fall dig the roots and place them in coldstorage. In early fall, when roots are 6–7 inches longand 1–2 inches wide at the crown, lift them from theground and trim the tops to 2 inches. Smaller rootswill not produce a tight bud of leaves, and largerroots will produce several buds that are too looseand small. Store the roots at 32–40°F to encouragedormancy and high relative humidity so they do notwilt. Check your seed package for the length of timeneeded for cold storage, since cultivars vary from afew weeks to several months. After cold storage,place roots upright in boxes or pails of damp sand,compost, or peat and cover them 1 inch deep. Keepthe boxes at 50–60°F and 95% humidity in the dark.In 30 days or so, buds form. Lower temperatures willproduce tight, round buds more slowly, and highertemperatures will produce elongated looser budsmore quickly. Cut the buds just above the soil linewith a sharp knife when they are 4–6 inches long.Keep them in the dark until consumed, since light willturn leaves green and make them more bitter. Rootswill resprout for a second and third harvest.

Endive and escarole cultureCultural practices for curly endive and escarole aresimilar to those for lettuce, but they tolerate greatertemperature extremes than lettuce. Both grow well in60–75°F weather, and unless they are bred for daylength adaptability, will tend to bolt under longsummer days with hot temperatures. Also, hotweather tends to make leaves taste more bitter. Curlyendive tolerates heat well and escarole toleratescold. Blanching (preventing light from reaching theleaves) will reduce the bitterness of endive andescarole. Planting close together helps self-blanch-ing cultivars keep out light. Plant 1⁄4-inch deep inspacings as you would lettuce, 8 inches apart forheads and 1 inch apart for salad mix. You can directseed or start transplants indoors. To blanch interiorleaves on a head, wait late enough in the day to drythe leaves and then tie the outermost leaves togetherfor 2 weeks before harvest. Endive and escarole dobest with constant soil moisture, which reduces tipburn on leaves.

Swiss chard cultureChard can be planted as early as mid-April andplanting can continue every four weeks or so until 30days before frost for salad mix and 60 days beforefrost for full sized leaves. Cold temperatures caninduce bolting which stops leaf growth and makesleaves bitter. Plant either directly in the field or usetransplants. For salad mix, seed 1⁄2-inch deep andthin to 1 inch. For full-sized leaves, space plants8–12 inches apart in the row.

11Season extendersYou can lengthen the growing season by protectingplants from late spring frosts and early fall frosts.There are a variety of ways to prolong the growingseason, including planting on a southern slope,creating a warmer microclimate using floating rowcovers, clear plastic tunnels, cold frames, or green-houses made of plastic sheeting (“hoophouses” or“polyhouses”).

Floating row covers. Floating row covers of spun-bonded polypropylene allow sunlight and water topass through the fabric. They can be used to protectlow-growing crops from frost, to serve as windbreaks,and to protect against insect pests. Depending onthe fabric weight, row covers can provide 4–8°F offrost protection. Row covers allow you to plant saladgreens 3–4 weeks earlier in the spring and extendthe season 3–4 weeks later in the fall. They can bereused two to three seasons.

To use row covers, drape them over the crop orsupport them with wire hoops. Gather the edges in aloose accordion-type fold and loosely bury them insoil along the crop row. As the crop grows it will pushup enough fabric to maintain a “floating” cover. Withcrops that will grow to market maturity under rowcovers, consider supporting the row cover fabric toprevent abrasion damage to plants. Use 9-guagewire hoops spaced 6 feet apart and buried 1 footdeep on each side of the row.

Row covers can be held in place by burying theedges with weights such as reebar. Completely sealall four edges to the ground if you use row covers asan insect barrier. If not using row covers as an insectbarrier, remove row covers when the average dailytemperature is warm enough for crop growth. Besure to vent the beds on hot days and to let plantsharden off for a few days to prevent burning beforecompletely removing the row covers. Harden plantsby removing covers on overcast days or for a fewhours on sunny days.

Tunnels and cold frames. Tunnels are large,unheated plastic-covered hoops that can be used toextend the growing season. Slitted clear poly tunnelsincrease daytime temperatures by 10–30°F andprovide 1–4°F of frost protection. Cold frames can beused to grow crops to maturity earlier in the springand later in the fall than would normally be possible.Consult the references at the end of this publicationfor more information on cold frames and tunnels.

Hoophouse, polyhouse, or greenhouse production.Salad greens lend themselves well to season exten-sion with greenhouses or plastic hoophouses. Youcan plant under shelter 4–6 weeks earlier thandirectly outdoors; some crops as early as February.Similarly, fall crops can be extended throughNovember before natural light levels become too lowand supplemental lighting becomes necessary.Floating row covers on top of crops grown underplastic can give additional insulation. Crops grown inthese structures can be grown from transplants ordirect seeded.

season extenders

Preventing high nitrate levelsSince plants require light to metabolizenitrate, higher levels of nitrate can accu-mulate in salad greens grown under lowlight. Nitrate can convert to nitrite, whichcan be toxic to humans. When growingleafy crops indoors under low light, thereare several practices you should follow tokeep leaf nitrate levels down:

■ Use minimal nitrogen fertilizer.

■ Sidedress the fertilizer instead ofbroadcasting it.

■ Apply several smaller doses of nitrogenthroughout the growing season ratherthan one large dose.

Cultivars of salad greens differ in theiraccumulation of nitrate. Spinach is espe-cially prone to accumulating nitrate.

12Soils and nutrientmanagementObtain a soil test for available nutrients beforeplanting a field for the first time and test routinelythereafter at least once every 3 years. After 3 years,soil conditions can change enough to make yourcurrent fertility management program obsolete. Forinformation on how to collect good samples andwhere to send them for analysis, see Extension publi-cation Sampling Soils for Testing (A2100).

Routine soil tests include pH, organic matter content,phosphorus, and potassium. Special tests are avail-able on request for nitrate-nitrogen, calcium, magne-sium, sulfur, boron, manganese, and zinc. You willreceive the results of your soil test along with fertilizerrecommendations based on your cropping historyand planned use of the field. You can also test yourpotting mix and the soil you intend to use for indoorproduction of salad greens.

Soil pHSoil pH varies between the various salad greens butgenerally should range between 6.0–8.0 for optimumnutrient availability and to prevent deficiencysymptoms. For lettuce, 6.0–8.0 is optimal; forspinach, chicories, endive, and escarole, 6.0–7.5 isoptimal; and for chard 6.5–7.5 is optimal. If the pH isbelow 6.0, apply aglime to raise the pH.

Fertilizer needsPlants take up nitrogen as nitrate (NO3

–) orammonium (NH4

+), phosphorus as phosphate(P2O5), and potassium as potash (K2O). Thesechemicals, as fertilizers, can come from organic orinorganic sources. With adequate environmental con-ditions, soil microbes break down organic matter andsupply the chemical nutrients that plants need totheir roots. Organic fertilizers can also improve soiltilth and health. Inorganic fertilizers can be used toquickly supply nutrients to plants.

Table 3. Annual nitrogen, phosphate, and potash recommendations for leafy crops

Nitrogen Phosphate and potash

Organic Yield Soil test Amount to applya

matter Amount to apply goal categories P2O5 K2O

Vegetable % lb/a oz/100 sq ft tons/a lb/a oz/100 sq ft lb/a oz/100 sq ft

Lettuce, endive, <2.0 120 4.4 15-20 optimum 40 1.5 160 5.9

escarole, 2.0–9.9 100 3.7 high 20 0.7 80 2.9

radicchio, 10.0–20.0 80 2.9 very high — — 40 1.5

Swiss chard >20.0 40 1.5

Spinachb <2.0 100 3.7 4–6 optimum 20 0.7 50 1.8

2.0–9.9 80 2.9 high 10 0.4 25 0.9

10.0–20.0 60 2.2 very high — — 10 0.4

>20.0 30 1.1

aIf soil test is low or very low, increase rates according to the soil test recommendations.bIf you grow spinach along with other salad greens, follow the same nutrient recommendations as for lettuce.

13Organic fertilizers can come from a variety ofsources such as manures, compost, fish meal, andbone meal. Each material contains varying amountsof specific nutrients. Table 3 provides fertilizer rec-ommendations and table 4 lists organic fertilizersand the amounts of nutrients available in each. Formore information on this subject, refer to Extensionpublication Organic Soil Conditioners (A2305).

NitrogenSalad greens have a relatively shallow and small rootsystem, so they cannot explore a wide area of soil fortheir nutrient needs. Also, rapid, continuous growthencourages crisp high-quality leaves. Frequent smallapplications of fertilizer are more effective than a fewlarge applications. Adequate nitrogen is necessaryfor optimum growth of all salad greens. On mineralsoils, broadcast no more than one half of the nitrogenduring field preparation and band or sidedress theremainder later, such as at thinning. On muck soils,apply all of the recommended nitrogen after fieldpreparation. Supplemental nitrogen may be neededthroughout the season to meet the plant’s needs,since 75% of the plant biomass is accumulated in thelast few weeks before harvest. A combined nitrateand ammonia-based nitrogen fertilizer will provideboth rapid and sustained nitrogen release.

MicronutrientsLettuce is prone to micronutrient deficiency when thelevels of the essential nutrients are low. In particular,boron, copper, zinc, and molybdenum deficienciesmay occur in lettuce grown on alkaline soils. Spinachis prone to many of the same micronutrient deficien-cies including boron, copper, molybdenum and mag-nesium. Under droughty conditions, calcium maybecome deficient, causing tipburn on salad greens.This physiological disorder occurs when high tem-perature and low water uptake causes rapid growthand decreased transpiration, reducing calcium trans-port to the developing tissues.

IrrigationBecause of the large leaf area, their high transpira-tion rate, and their small shallow root system, saladgreens require regular irrigation, particularly onsandy soils. Irrigation is often helpful prior to germi-nation to prevent a crust from forming on the soil. Ifleaves begin to wilt mid-day, plants are moisturestressed. Plants that wilt intermittently producesmaller yields than plants that are not allowed to wilt,while plants that wilt frequently or for too long willoften die due to irreversible cell damage. Lettuce isparticularly prone to wilting. Spinach is less demand-ing of supplemental irrigation, because it has a shortlifespan which occurs during the cool part of thegrowing season.

Both drip and overhead sprinkler irrigation systemsare effective. These systems include trickle tape,solid set, and traveler hose wheel. Drip irrigationsystems will reduce the incidence of foliar diseasescaused by excess leaf moisture.

Irrigation scheduling software is available from theUniversity of Wisconsin-Extension to help you deter-mine your irrigation needs. For more information onthis software, contact your county Extension agent.

soils and nutrient m

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ation

Table 4. Nutrient composition of various

organic fertilizers

Material N P2O5 K2O

———— % ————Alfalfa hay 2.0–3.0 0.2–0.6 2.0–3.2

Bone meal 0.2–1.0 12.0–14.0 —

Composta 0.5–3.5 0.5–1.0 1.0–2.0

Fish meal 9.0–11.0 5.0–8.0 0.0–3.0

Greensand — — 7.0

Manure, cow 0.5–0.7 0.2–0.4 0.5–0.8

Manure, sheep 1.0–2.0 0.7–1.0 0.5–2.0

Manure, poultry 1.1–1.7 1.0–1.3 0.5–1.0

Rock phosphate — 20.0–30.0 —

Soybean meal 7.0 0.5 2.3

aNutrient analysis of compost will vary based on the source.

14Harvest, handling, and storageAlmost all salad greens are hand harvested in theMidwest. Growers either pick the outer, older leavesfrom each plant or clip all the leaves at once. Withboth methods, new leaf growth occurs and severalharvests are possible from each planting. The daysfrom planting to harvest vary depending on the cropbeing grown and the weather conditions. Sampleyour own crop frequently to determine the best timeto harvest under your conditions. You will be yourown best sales representative if you learn to recog-nize and describe produce quality. Most leafy greenscan be harvested from immature stages until theyjust begin to lose peak flavor. Some become bitter ifharvested too late. Also, plants harvested late aremore susceptible to postharvest diseases. Somegrowers sell “micro” greens: tiny leaves harvestedwhen the first true leaves appear. Micro greens areused in salad, in place of sprouts, or as a garnish.

Harvest individual leaves by plucking them from theplant, bunches of leaves by cutting them with asharp knife or shears, and lettuce and radicchioheads by cutting them with a sharp knife. Cut headsbelow the lowest leaf and remove any damagedleaves. Harvest salad greens into a container linedwith a polypropylene mesh bag, such as a laundrybag. This will reduce handling time postharvest.

Salad greens retain their fresh crisp taste if they arehydrocooled and kept under high humidity.Hydrocool them by submerging the mesh bagfuls ofcrop in a cool water bath for several minutes immedi-ately after harvest. If the leaves are gritty or dirty,change the water for a second or third rinse. Buy ormake washtubs large enough to fit your operation.You can use barrels made of food-grade plastic,which are available secondhand from dairy supplyhouses or food processing plants. Cut the barrels inhalf lengthwise and build a wooden framework tosupport them at a good working height (see picture).Cut a hole in the short end to insert a PVC elbow andvalve (from the plumbing supply section of yourhardware store) that you can fit into a long PVC pipeto drain the water away from your workstation. Orchoose a bigger tank to wash greens, such as a

recycled stainless steel bulk milk tank from a dairyfarm. Some growers have fitted motors from whirlpoolbaths into bulk milk tanks to create a bubble-typewashing system for salad greens.

Dry greens by spinning them for a few minutes orlaying them out on screen tables. You can spin dry asmall amount of washed greens by swinging themesh bag in circles over your head lasso-style.Larger quantities can be dried by placing two meshbags of greens into a secondhand washing machineset to spin cycle for a few minutes. Some growersremove the center agitator from the machine. Othergrowers use large restaurant salad spinners poweredby an electric motor.

Pack greens into waxed cardboard boxes and storethem in a cooler. Maintain humidity and provideevaporative cooling by lining the box with a cleandamp cloth. Make sure that temperatures do not fallbelow 32°F, since freezing can harm the crops.Ethylene, a gas given off by ripening apples, melons,pears, plums, and tomatoes will also reduce thequality of salad greens and cause them to yellow. Donot store these crops in the same cooler as saladgreens. Sell greens bulk by the pound or in plasticproduce bags as soon as possible after harvest.They can be kept in a cooler for 1–2 weeks.

Washtubs made from plastic barrels.

Lettuce should be harvested when plants reach asuitable size for the cultivar grown. For crispheadlettuce, the heads should yield slightly to pressure.Crisphead lettuce is ready to harvest approximately60–120 days after planting, depending on weatherconditions and cultivar grown. Butterhead lettuce ismature in 42–70 days, romaine in 50–70 days, andleaf lettuce in 48–58 days. All of the lettuce typesexcept crisphead have excellent quality as animmature crop, and can be harvested startingapproximately 3 weeks before full maturity.Butterhead and leaf lettuce have more tender leavesand more exposed leaf surfaces, so they are moreperishable than crisphead or romaine lettuce.Lettuce should be stored at 33–35°F and 90–95%relative humidity.

Spinach matures in 35–50 days and can be har-vested once five to seven leaves have formed.Continue harvesting until the new leaves producedbecome too small or a seed stalk forms. Typically anaverage of 25 leaves per plant can be expected.Spinach keeps well if stored at temperatures of 32°Fand a relative humidity of 85–95%.

Harvest radicchio when heads are the appropriatesize for the cultivar grown, approximately 60–90 daysafter planting, and store for up to 2 weeks at 32°Fand 95% relative humidity. Endive and escarolereach full maturity in approximately 52–90 daysdepending on cultivar and growing conditions. Theycan also be harvested as immature greens beginning3 weeks earlier. Like radicchio, they should be keptat 32°F and 95% relative humidity and will keep forup to 2 weeks. Harvested witloof maintains freshnessfor only a few days. Store it in the dark at 32°F and95% relative humidity.

Swiss chard matures in 50–60 daysbut can also be harvested asimmature leaves approximately 3weeks before full maturity. Storechard at temperatures of 32°F and arelative humidity of 85–95%.

15harvest, hand

ling, and

storage

Harvesting&packing tips

Growing salad greens can involve a lot of stooplabor during thinning, weeding, and harvesting.Change your position often to minimize stress andfatigue to your body. Some growers sit on a one-legged field stool that straps on with a waist belt.Others sit on a cart that straddles the crop rows(plans for building a customized cart are availableonline at www.bse.wisc.edu/hfhp). Slow-movingtractors are available that straddle the crop row andallow workers to lie face down with their hands freeto harvest. Some growers have fitted thesemachines with a handheld power band saw andvacuum system to cut and collect leafy greens.Other options include small-scale harvesters thatare pulled behind a tractor and are either powertake-off (PTO) driven or self-propelled. Somegrowers modify lightweight hedge shears to harvestsalad greens by attaching a rectangular piece ofthin sheet metal to the bottom of each blade andbending it up at a 90° angle to form a scoop (seepicture). They use both hands to cut the greensand then tip the shears into a container to empty thegreens.

Use garden carts and wagons as much as possibleto minimize lifting and hand carrying heavyproduce. Standardized vented plastic containersthat stack are easy to load, unload, and clean.

With a smooth level floor in the packing area, a pal-letized packing and storage system can bedesigned to fit small-scale operations (small palletsmoved with a hand-pushed pallet truck) or largeoperations (pallets moved by forklift). Heavy boxesof produce can be moved from one area to anotheron roller tables.

Lay out your washing and packing area to minimizestooping, lifting, and carrying. Set up work stationsand water baths at table height. Ideally tables couldbe adjusted to match each worker, so that work isperformed at a height between wrist and elbowwhen the arm hangs at the worker’s side.

Modified hedge shears.

Insect management

AphidsDescription: Aphids are small, soft-bodied, pear-shaped insects thatcome in a variety of colors. Theycan be distinguished from all othertypes of insects by the presence ofcornicles, or tailpipes, projectingfrom the back end of the insect.

The bean, green peach, potato, and melon aphidscommonly infest salad greens. All species can bewinged or wingless and may reach 1⁄8 inch in length.Immature bean aphids are green and spotted withwhite wax while the adults are dark green or sootyblack in color. The green peach aphid has an elon-gated, smooth, soft, spindle-shaped body. Antennaeare held to the side and are longer than the body.Coloration varies from green to reddish-pink. Wingedforms are a pale green. Potato aphids have moreslender bodies and longer legs and are more active.Melon aphids are 1⁄16 inch long and vary from paleyellow to dark green or black with black cornicles. Allspecies have piercing/sucking mouthparts and feedby sucking on plant juices.

Life cycle: In Wisconsin, bean aphids overwinter aseggs on euonymous and viburnum while greenpeach aphids overwinter on the bark of peach, plum,apricot, or cherry trees. Potato aphids overwinter aseggs on wild and cultivated roses and melon aphidssurvive the winter on a whole host of woody plants.During the summer, adult female aphids produce off-spring without mating or laying eggs. In warmweather a female can give birth to as many as 12nymphs per day.

Nymphs mature in less than 2 weeks. Late in theseason, the females mate and produce eggs that willoverwinter. Individual generations may be completedwithin 1 week during the summer, and multiple gen-erations overlap. Aphids produce winged offspringwhen colonies become overcrowded and when daylength begins to shorten. Colonies live primarily onthe underside of leaves, usually in the lower canopy.

Damage, symptoms: Aphids feed by inserting a fine,needle-like stylet between plant cells into thevascular tissue. Typically, this causes little directinjury to adjacent tissues. Extremely large popula-tions may extract enough sap to cause leaf curlingand wilting or eventual plant death. Seedlings aremost susceptible to aphid damage, although saladgreens of any size may be killed by heavy aphidfeeding. Aphids excrete excess sap, calledhoneydew, which falls onto leaves, giving them asticky texture. Sooty mold fungi may grow onhoneydew secretions, making affected greensunmarketable. Aphids are capable of transmittingmany viruses that affect lettuce and other saladgreens.

Management: Scout weekly for aphids by examining30 plants per field up to 10 acres. Add 10 plants foreach additional 10 acres. Examine the entire plant,paying close attention to the lower leaf surfaces.Count the number of adult and nymph aphids. Treat ifyou find more than 3 aphids on seedling plants ormore than 10 aphids per plant on established plants.Monitor whether populations are increasing ordecreasing over time.

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Conservation of natural enemiesNot all insects are pests. Beneficial insects prey on

other insects, helping to keep popula-tions in check. You can take

advantage of this free naturalresource by minimizing the useof broad-spectrum insecticides.

For more information about biologi-cal controls, see Extension publication

Biological Control of Insects and Mites: AnIntroduction to Beneficial Natural Enemies

and Their Use in Pest Management (NCR481).

Natural controls such as heavy rains, predators, anddiseases may help reduce aphid populations.Predators include ladybird beetles, lacewings, andsyrphid flies. Often though, aphids reproduce farfaster than the parasites and predators can consumethem.

Systemic and foliar insecticides provide goodcontrol. However, insecticides often also destroy thebeneficial natural enemies, resulting in secondaryaphid problems. In addition, many populations ofgreen peach aphids have high levels of insecticideresistance. Insecticides should be applied for otherinsects only when needed, as determined byscouting.

Aster leafhopperDescription: The aster leafhopper is aserious pest of salad greens because ittransmits the aster yellows phyto-plasma. Adult aster leafhoppers areolive-green, wedge-shaped, and about1/5 inch long. Adults have six spots onthe back of the head. Nymphs aresimilar in shape to the adults, but are

cream colored and lack fully developed wings.Adults are extremely active and jump, crawl, or flywhen disturbed. Nymphs are less active but crawlrapidly.

Life cycle: The first leafhoppers that appear eachseason migrate from the Gulf states. Each year theyare carried on warm, southerly winds. Large influxesmay occur in June and early July as local popula-tions develop. Adult females lay eggs in the leaves ofsusceptible plants. Nymphs hatch 5–7 days later andmature in 20–30 days. There are normally two to fivegenerations per year.

Damage, symptoms: Both nymphs and adults feed byinserting piercing-sucking mouthparts into the plantto extract sap. If a leafhopper feeds on an infectedplant, it ingests the aster yellows pathogen. When theleafhopper moves to another plant to feed, it trans-mits the pathogen in its saliva. In lettuce, diseasesymptoms appear about one month later. Initialsymptoms of aster yellows is a generalized chlorosisfollowed by a stunting and twisting of the leaves.

Management: Aster leafhoppers may be effectivelycontrolled by excluding them from the planting usingfloating row covers. Row covers should be in placefrom the time the lettuce emerges or is transplanteduntil 30 days before harvest. (See the section onseason extenders for more information on floatingrow covers.)

If you’re not using row covers, the only effective wayto prevent the spread of aster yellows disease isthrough insecticidal control of aster leafhoppers. Tocontrol leafhoppers, you need to know both the sizeof the population and the percent of the populationthat’s infective. Place sticky cards in the field whenthe crop emerges. The cards should be just abovethe crop and a few rows in from the outer field edge.Begin scouting weekly when you find leafhoppers onthe cards. Use a sweep net to take 25 sweeps persite, and sample two sites per acre. Each spring, theUniversity of Wisconsin-Extension collects samplesof migrating leafhoppers and determines the per-centage that are infective. For current information,contact your county Extension office. If the percent ofinfectivity is not known, use 2.5% for the followingcalculations. To decide whether treatment is neces-sary, multiply the number of leafhoppers per 100sweeps by the percent infectivity of the migrant pop-ulations. Treat when an index of 25 is reached.Because it takes a month for the symptoms of asteryellows to develop, treatment may be discontinued2–3 weeks before harvest.

Remove weeds from field edges as these may be areservoir for the pathogen. Avoid planting suscepti-ble crops near untreated crops or weeds that theleafhopper uses for refuge. If not using insecticidesor row covers, consider planting an additional 30% tooffset losses due to aster yellows.

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Black cutwormDescription: Cutworms arethe larvae of nocturnalgray moths. They tend tofeed at or just below theground surface at night.Cutworms are active

feeders on young foliage and stems and will cut offmany young seedlings in an evening. The large(11⁄2–2 inches), fleshy larvae curl up into a tight C-shape when disturbed.

Life cycle: Few cutworms overwinter in Wisconsin.Beginning in late May, moths migrate into the state.Female moths lay hundreds of eggs either singly orin clusters. Most eggs are laid on low-growing,grassy vegetation or plant residue from the previousyear’s crop. Once the eggs hatch, the young larvaefeed above ground on the tips of plants. Largerlarvae feed at or just below the soil surface at nightor on cloudy days. During the day they hide in thesoil or beneath foliage. There are three to four gener-ations per year in Wisconsin, but the first generationis the most damaging because it coincides withseedling plants.

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Temperature affects the rateof development of plantsand insects. Cold weatherslows development whilewarm weather accelerates it.For this reason it is mislead-ing to describe developmentin terms of time alone. Tomonitor crop developmentand predict pest behavior,professional pest managersoften use a system thattakes into account the accu-mulation of heat withpassing time. This system isbased on degree days (DD).

A degree day (DD) is a unitof measure that occurs foreach degree above a basetemperature during a 24-hour period. The base tem-perature is the temperature

below which there is noplant or insect development.Specific insects havespecific base temperatures.Most plants use a base tem-perature of 50°F. Cool-season plants, such aspeas, grow in cooler temper-atures and have a base tem-perature of 40°F. Beginrecording degree day accu-mulations for Wisconsin onMarch 1.

To monitor plant and insectdevelopment using degreedays, you will need amaximum/minimum ther-mometer to obtain the dailyhigh and low temperatures.Calculate degree days usingtheequations below.

Example: Assume you haveaccumulated 200 degreedays to date using a basetemperature of 40°F. If yes-terday’s high temperaturewas 75°F and the low was60°F, then the daily averagetemperature would be67.5°F [(75 + 60) ÷ 2]. Tocalculate the degree dayaccumulation, subtract thedaily average from the basetemperature for a total of27.5DD (67.5 – 40). Add thisnumber to the total numberof degree days to date(27.5 + 200) for a new totalof 227.5.

(daily higha + daily lowb) ÷ 2 = daily average temperaturedaily average temperature – base temperature = degree day accumulationaUse 86°F if the high temperature for the day is more than 86°F.bIf the daily low is less than the base temperature, use the base temperature.

Calculating degree days

Damage, symptoms: One large larva may destroyseveral plants in one evening. The larvae often pullthe stem of the severed plant into their subterraneanburrows.

Management: Since female moths prefer to lay eggsin grassy areas, controlling grassy weeds lessens thepossibility of problems. Avoid planting in low, wetareas or in areas where grassy plants or weedsexisted the previous year. Insecticides may be usedin areas where cutworms historically have been aproblem. Fields should be scouted if feedingdamage is observed. Scout for cutworms by lookingfor wilted plants or plants with severed stems. Thereis no established threshold for treatment of cutwormsin lettuce but growers usually become concernedwhen more than 3% of the planting is affected.

Spinach leafminerDescription: The spinach leafminer can causespinach, chard, and occasionally other leafy greensto become unmarketable as a result of their feeding.The spinach leafminer is the larval stage of a small,gray fly with black bristles.

Life cycle: The adult flies lay one to five elongate,white eggs on the lower leaf surface of older leaves.The eggs hatch within 3–6 days and legless, yellow-white maggots burrow into the leaf and beginfeeding between the upper and lower leaf surfaces.A single larva may mine more than one leaf during its2-week life span at which time they will drop to theground to pupate. There can be three or four genera-tions a year. Damage is most severe in early planti-ngs but is possible throughout the season.

Damage, symptoms: Initial feeding damage appearsas slender, winding mines. As the maggots grow, themines become joined together to produce large,light-colored blotches that are filled with excrement.Damaged leaves are unmarketable.

Management: Floating row covers can be used toexclude the flies from laying eggs on leafy greens.(See the section on season extenders for detailsabout timing and placement of row covers.) Theremoval of weedy hosts such as lambsquarters canalso reduce the number of flies in the area and deepspring plowing will destroy any overwintering pupae.

There are no thresholds for the spinach leafminer, butif eggs are found on more than 50% of seedlingcrops, treatment should be implemented. Thresholdson established crops will vary with the market andhow much damage the customer will tolerate.Typically, if more than 5% of the leaves have mines,treatment is warranted. Note that pesticides will notcontrol maggots once they burrow into the leaves, sotiming is critical.

Disease management

Aster yellowsHosts and severity: Aster yellows is a potentiallyserious disease of salad greens as well as manyother vegetables and ornamental flowers. Thedisease is caused by a phytoplasma organism whichis similar to a virus.

Disease cycle: The phytoplasma that causes asteryellows is transmitted by at least 17 species ofleafhoppers. The pathogen overwinters in the bodiesof adult leafhoppers or in perennial host plants suchas weeds and ornamentals. Leafhopper nymphs andadults acquire the pathogen through feeding oninfected plants. Once inside the leafhopper, the phy-toplasma multiplies. An incubation period of at least10 days must pass before the leafhopper cantransmit the pathogen back to the plants. The insectmay remain infective for at least 100 days. Plants firstshow symptoms 30 days after they become infected.

Symptoms: Symptoms of aster yellows first appear asa yellowing of the leaf tissue especially of the heartleaves of heading types of lettuce. Leaves may alsobe twisted and disfigured. Infected lettuce leaveshave a bitter taste. Escarole also turns yellow, but theleaves do not become distorted. Endive becomesseverely stunted and chlorotic.

Management: There is no cure for aster yellows, socontrol is aimed at disease prevention. Controlleafhoppers or exclude them from susceptible cropsusing floating row covers. Also, remove weeds fromfield edges that may serve as a reservoir for thepathogen.

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Cercospora leaf spotHosts and severity: Cercospora can be a seriousdisease of spinach and chard in wet years, causingdeath of the entire leaf that is affected.

Disease cycle: The fungus overwinters on infectedplant debris and wild hosts such as Queen Anne’slace. Spores produced on this debris are carried bywind or water to young leaves. The fungus enters theplant through pores in the leaf (stomata). Lesionsappear after 3–5 days and new spores are producedsoon thereafter.

Symptoms: Early symptoms appear as tiny, water-soaked spots that enlarge to form larger, irregular,brown spots surrounded by a purple border. As thespots enlarge, the centers become whitish grey.Spores of the Cercospora fungus are produced inthe center of these lesions. In time, the center tissuebecomes dry and brittle and falls out. Older leavesare infected first and infection may be severe enoughto kill the entire leaf.

Management: Fall plowing to hasten decompositionof infected debris coupled with a 2- to 3-year croprotations will aid in the control of Cercospora leafblight. Balanced fertility will also reduce crop sus-ceptibility. Protectant fungicides may be necessary.

Mosaic virusesHosts and severity: Lettuce mosaic virus (LMV) is oneof the most damaging diseases of lettuce, spinach,escarole, and endive. The cucumber mosaic virus(CMV) infects both lettuce and spinach. In the caseof the latter, the syndrome is referred to as spinachblight. At least 34 plant families serve as hosts toCMV while 12 plant families are susceptible to LMV.

Disease cycle: LMV is primarily seedborne with up to3–5% of the seed being infected. The virus can alsooverwinter in weeds. The green peach aphid carriesthe virus between hosts. Aphids, most commonly thegreen peach aphid, are also responsible for thespread of CMV. This disease can be acquired fromweedy host plants by aphids and transmitted to sus-ceptible hosts within minutes. Infection is favored bywarm temperatures and symptoms progress rapidlyat temperatures above 82°F.

Symptoms: The symptoms of LMV differ dependingon age of plant, variety, and time of infection. Seed-borne infection produces plants with irregularlyshaped leaves. Under cool, cloudy conditions,infected leaves on older plants become mottled. Insome varieties, leaves turn brown.

Initial symptoms of CMV on spinach appear as amottling of the younger leaves. As the diseasedevelops, leaves become yellow and crinkled. Thegrowth of seedling plants becomes stunted. Inlettuce, leaves become stunted and mottled yellow.

Management: Early spring spinach and lettuce cropsoften escape infection. Destruction of perennial weedhosts of the virus will reduce the chance of infection.Once plants become infected with either virus, thereis no cure. Controlling the aphids that carry thedisease is often a key for successful management.Plant spinach, lettuce, endive, and escarole awayfrom previous plantings of these crops, particularly ifinfection occurred the previous year. Also, avoidplanting spinach and lettuce near cucurbits whichare also a common host for CMV. The spinach culti-vars Melody Hybrid, Tyee, and Bloomsdale Long-Standing are resistant to the cucumber mosaic virus.No lettuce cultivars are resistant to CMV, thoughresearch continues to explore this possibility. Lettucecultivars Esmerelda, Nevada, Parris Island,Prizehead, and Sierra are all resistant to LMV.

Damping OffHosts and severity: Damping off is one of the firstdiseases to appear after seedlings emerge. All veg-etable seedlings are susceptible. Two fungi arecommonly associated with damping off of lettuce:Pythium spp. and Fusarium spp. The pathogensinfect plant roots soon after germination. The tissueat or below the soil line becomes soft and can nolonger support the plant, causing it to topple. Asplants mature, the stems become more woody andresistant to infection. Damping off is often limited tolow spots of the field. Heavy, wet soils tend to havemore problems with this disease than lighter, well-drained soils. Excess nitrogen can increase the inci-dence of disease.

20

Disease cycle: The fungi that cause damping off aresoilborne and infect the roots of seedlings soon aftergermination. Pythium can live in the soil 2–3 yearswhile Fusarium can survive in the soil for 5 years ormore.

Symptoms: The first sign of infection is the presenceof small, firm, dark green spots. These spots laterturn tan or brown and collapse. In wet weather,threadlike, white to cream-colored mycelium maycover the lesions.

Management: To prevent outbreaks on transplants,use sterile, soilless potting mix. Direct-seeded plant-ings may be protected by treating the seed with afungicide prior to planting. Planting high-quality seedwhen conditions are favorable for rapid germinationand growth will reduce the chance of infection. Croprotations out of salad greens for at least 4 years arerecommended.

Downy mildewHosts and severity: Downy mildew in spinach is oftenreferred to as “blue mold” and is caused by thefungus Peronospora effusa. It is a serious diseasewherever spinach is grown. Under favorable weatherconditions, an entire crop may be lost in a matter ofdays.

Disease cycle: The fungus overwinters in infectedplant debris and in the soil. In the spring, thesespores germinate. Like other water mold fungi, itrequires free water to cause infection. When theycome into contact with a susceptible plant, infectionoccurs.

Symptoms: The initial symptoms appear as irregular,chlorotic lesions on the leaves. During cool, wetweather conditions, the fungus produces blue-grayfruiting structures on the upper and lower leafsurfaces giving the name “blue mold” to the disease.The spots continue to enlarge until they cover theentire leaf and the leaf becomes black and dies.

Management: Growers should practice a 3-year croprotation out of spinach to reduce the likelihood ofinfection. Planting in well-drained soils or raised bedsis also recommended. Resistant cultivars such asMelody, Olympia, Space, and Tyee are recom-mended for planting in areas where downy mildewhas been a problem.

Lettuce bottom rotHosts and severity: Bottom rot is a destructive fungaldisease of lettuce caused by Rhizoctonia solani. Thelower leaves of heading lettuce cultivars that comeinto contact with the soil become infected and rot. Awide range of plants can serve as host to theRhizoctonia fungus. All types of lettuce, escarole,and endive are susceptible.

Disease cycle: The fungus that causes bottom rotoverwinters as mycelium on infected plant debris oras sclerotia in the soil where it can survive indefi-nitely. The disease can be spread by any means thatmoves soil from one location to another. Warm, moistconditions favors infection. The fungus enters theplant through wounds or natural openings such asstomata. As the infection progresses, spores areproduced on the host. These spores can besplashed or blown long distances to infect otherplants.

Symptoms: Symptoms of bottom rot usually don’toccur until lettuce has already headed and is nearlymature. Sunken, rust-colored lesions appear on themidrib of leaves that come in direct contact with soil.Often, the first symptom noticed is when the outerwrapper leaves begin to wilt. As the infection pro-gresses, leaves decompose and the infection movesinward, eventually infecting the entire head. Anamber fluid oozes out of infected leaves.

Management: Plant on well-drained soils or in raisedbeds and space plants to assure adequate air circu-lation to promote drying of the foliage. Rotate out ofsusceptible crops for a minimum of 3 years.Protectant fungicides may be necessary whenweather conditions favor disease.

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Sclerotinia dropHosts and severity: The fungus that causesSclerotinia drop, Sclerotinia sclerotiorum, affects awide range of succulent plants. It occurs in alllettuce-growing regions where cool, moist conditionsexist.

Disease cycle: The fungus overwinters on live hosts,on infected plant debris, or as sclerotia in the soil. Inthe spring, the sclerotia germinate and produce astructure in which numerous spores are produced.These spores are spread to susceptible hosts bywind. Sclerotia germinating near lettuce plants caninfect nearby plants directly.

Symptoms: The disease gets its name from the waythe leaves of heading forms of lettuce “drop” in latestages of infection. Initial symptoms appear as awater-soaked lesion on the stem near the soilsurface. From this point, the disease spreadsdownward to infect the root system and upwardwhere a petiole rot causes leaves to wilt and die. Theolder, bottom leaves are affected first but the diseasecontinues to spread until it reaches the interior of thehead. Under wet conditions, the fungus produces awhite mat of mycelium.

Management: Plant lettuce on light, well-drained soilsor in raised beds. Space plants adequately far apartto promote rapid drying of the foliage during wetweather. Long rotations with resistant crops such ascorn, grasses, or small grains should be practiced toprevent a build-up of inoculum in the soil and subse-quent outbreaks of disease. Good weed control isalso important to limit infection of alternate hosts.Chopping plants before incorporating the debris intothe soil in the fall will hasten decomposition andreduce the potential of the pathogen overwintering.

Weed managementWeed management is essential for crops to producemaximum yields. Weeds compete with crop plantsfor sunlight, water, nutrients, and space. It is essen-tial to eliminate perennial weeds before planting. Dothis by smothering with a cover crop (such as buck-wheat), by heating the soil with black plastic, byhand removal, or by using herbicide sprays. Cultivateor hoe regularly to control annual weeds. Cultivatingearly in the season reduces weed impact the most.Pre-emergent herbicides may be used to clean upany annual weeds present in the field at the time ofplanting.

Salad greens are poor competitors with weedsbecause of their small shallow root system, and therelatively small leaf canopy they produce ascompared with beans, tomatoes, or vine crops.Weeds get in the way of harvest and easily contami-nate the finished product. Shallow cultivation will helpreduce root damage to the crop. Sometimes handcultivation or hand weeding is necessary. The lay-down tractors described in the harvest section arealso useful to carry workers comfortably for handweeding.

Refer to Extension publication Commercial VegetableProduction in Wisconsin (A3422) for specific herbi-cide recommendations.

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Additional reading

Culture2003 High Tunnel Production Manual. Bill Lamont.2003. University Park, PA: The Pennsylvania StateUniversity Center for Plasticulture.

Direct Marketing of Farm Produce and HomeGoods—Direct Marketing Alternatives and Strategiesfor Beginning and Established Producers (A3602).John Cottingham, James Hovland, et al. 1994.University of Wisconsin-Extension.

Gardening Under Plastic: How to Use Fleece, Films,Cloches, and Polytunnels. Bernard Salt. 2003.London: Batsford Gardening Books.

Growing for Market Newsletter. FairplainPublications, P.O. Box 3747, Lawrence, Kansas66046. www.growingformarket.com. A monthlynewsletter with practical articles on all aspects ofsmall-scale fresh market farming.

Harvesting Vegetables from the Home Garden(A2727). H.C. Harrison. 1996. University ofWisconsin-Extension.

The Hoophouse Handbook: Growing Produce andFlowers in Hoophouses and High Tunnels. 2003.Fairplain Publications, P.O. Box 3747, Lawrence,Kansas 66046.

Knotts Handbook for Vegetable Growers, FourthEdition. Donald N. Maynard and George J.Hochmuth. 1997. Wiley.

The New Organic Grower. Second Edition. EliotColeman. 1995. Chelsea Green Publishing.

The New Seed Starters Handbook. Nancy Bubel.1988. Rodale Press.

Soil Test Recommendations for Field, Vegetable, andFruit Crops (A2809). K.A. Kelling, L.G. Bundy, S.M.Combs, and J.B. Peters. 1998. University ofWisconsin-Extension.

Storing Vegetables at Home (A1135). H.C. Harrison.1996. University of Wisconsin-Extension.

Sustainable Vegetable Production From Start-up toMarket. Vernon P. Grubinger. 1999. NaturalResource, Agriculture, and Engineering ServiceCooperative Extension.

Rodale’s All New Encyclopedia of OrganicGardening. Edited by Fern Marshall Bradley andBarbara W. Ellis. 1992. Rodale Press.

Vegetables of Canada. Derek B. Munro and ErnestSmall. 1997. National Research Council of Canada.

Work Efficiency Tip Sheets. Healthy Farmers, HealthyProfits Project. University of Wisconsin-Madison.www.bse.wisc.edu/hfhp/. Work efficiency tools forsmall-scale vegetable farmers.

World Vegetables: Principles, Production, andNutritive Values. Second Edition. Vincent E. Rubatzkyand Mas Yamaguchi. 1997. Chapman and Hall.

PestsBiological Control of Insects and mites: An introduc-tion to Beneficial Natural Enemies and Their Use inPest Management (NCR481). Daniel L. Mahr andNino M. Ridgway. 1993. University of Wisconsin-Extension.

Commercial Vegetable Production in Wisconsin(A3422). C.M. Boerboom et al. Updated annually.University of Wisconsin-Extension.

Identifying Diseases of Vegetables. A.A. Macnab,A.F. Sherf, and J.K. Springer. 1983. PennsylvaniaState University College of Agricultural Sciences.

Pests of the Garden and Small Farm: A Grower’sGuide to Using Less Pesticide. Mary Louise Flint.1998. University of California Press.

Rodale’s Color Handbook of Garden Insects. AnnaCarr. 1979. Rodale Press.

Vegetable Insect Management with Emphasis on theMidwest. Rick Foster and Brian Flood, editors. 1995.Meister Publishing Company.

Weeds of the North Central States. North CentralRegional Research Publication No. 281. 1981.University of Illinois at Urbana-Champaign, Collegeof Agriculture.

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Copyright © 2003 University of Wisconsin-System Board of Regents and University of Wisconsin-Extension,Cooperative Extension.

Authors: K.A. Delahaut is horticulture outreach specialist for the Fresh Market Vegetable Program, College ofAgricultural and Life Sciences, University of Wisconsin-Madison and University of Wisconsin-Extension,Cooperative Extension. A.C. Newenhouse is assistant scientist for the Wisconsin Healthy Farmers, HealthyProfits Project of the department of Biological Systems Engineering, College of Agricultural and Life Sciences,University of Wisconsin-Madison. Produced by Cooperative Extension Publishing, University of Wisconsin-Extension.

University of Wisconsin-Extension, Cooperative Extension, in cooperation with the U.S. Department of Agriculture andWisconsin counties, publishes this information to further the purpose of the May 8 and June 30, 1914 Acts ofCongress; and provides equal opportunities and affirmative action in employment and programming. If youneed this material in an alternative format, contact the Office of Equal Opportunity and Diversity Programs orcall Cooperative Extension Publishing at 608-262-8076.

This publication is available from your Wisconsin county Extension office or from Cooperative Extension Publishing.Call toll free 877-WIS-PUBS (947-7827) or order online at cecommerce.wisc.edu.

A3785 Growing Salad Greens in Wisconsin: A Guide for Fresh-Market Growers I-9-03-1.2M

Partial funding for the printing of this publication was through a grant from the U.S. Environmental ProtectionAgency—Region V as part of their Agricultural Stewardship Initiative.