ANR-1135

A L A B A M A A & M A N D A U B U R N U N I V E R S I T I E S

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Guide to CommercialCabbage Production

Historical PerspectiveCabbage (Brassica oleracea L.

var. capitata) is a member of theBrassicaceae (Mustard) family(Figure 1). This family includesbroccoli, brussels sprouts, cauli-flower, kale, mustard (greens), andcollards. Collectively, these cropsare referred to as cole crops orcrucifers.

PlantingRecommendations

Planting Dates, Seeding,and Transplanting

Cabbage is a cool-season cropgenerally requiring 60 to 100 daysfrom sowing to reach market matu-rity, depending on the variety.Cabbage can be grown as a springcrop as well as a fall crop inAlabama. Although it can be direct-seeded, most cabbage productionrelies on the use of transplants.Ideal monthly temperatures foroptimal growth and developmentranges from 60°F to 65°F.

Temperatures over 75°F can in-duce “bolting” in cabbage, but vari-eties differ in their susceptibility tothis disorder. Bolting is the processin which the plant switches fromvegetative growth (heading) to re-productive growth (formation offlowers and seeds). This switch be-comes evident when seed stalksappear, making the heads unmar-ketable. The presence of a seedstalk is not always apparent fromexamining the exterior of the cab-bage; the head may have to be splitto see the seed stalk forming fromthe base of the plant. Many vari-eties differ in their tolerance tohigher temperatures that inducebolting. More information on vari-ety selection is discussed in theVariety Selection section of thispublication.

Direct-seeding of cabbage re-quires using a precision seeder toplace single seeds at the desiredplant spacing. Soil temperaturesmust be above 40°F to ensure

germination of the seed; otherwise,seed will be lost to rotting anddamping off, resulting in poor, un-even stands. The optimal range forgermination is between 45°F and95°F.

Some growers opt to producetheir own transplants in field bedswhere seed is scattered over a pre-pared area and then transplants aredug 5 to 7 weeks later. One ounceof cabbage seed will produce about5,000 transplants.

For a spring crop, transplant inlate December through earlyJanuary in South Alabama or in lateJanuary through early February inNorth Alabama. The fall cropshould be field-seeded during thefirst half of August in SouthAlabama and during the last half of July in other areas. If using trans-plants in the fall, plant about 1month later than if field-seeding.

Prepare the land early by turn-ing the soil so that any crop residueis fully decomposed before trans-planting or direct-seeding is done.Space plants 12 to 15 inches apartin 36- to 42-inch rows. This willproduce heads that range from 2 to3 pounds. When larger heads aredesired, increase the spacing

Figure 1. Well-formed head of cabbage

Early Greek and Roman litera-ture refers to the cultivation of colecrops for their perceived medicinalproperties as well as a source offood. Belief that these crops re-lieved such conditions as gout,deafness, and headaches furtheredthe spread of cole crops from theMediterranean through the OldWorld.

Now, cabbage and many of thecole crops are cultivated through-out the world for use fresh and inprocessed products. Nutritionally, 1 cup of raw cabbage contains 93percent water and is a good sourceof dietary fiber as well as vitaminsA and C. Worldwide, China is theleading producer and consumer ofcabbage. In the United States,80,000 acres of cabbage valued atalmost $280 million was harvestedin 1997. Figure 2. Characteristic symptom of

tipburn on exterior (top) cabbage head

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Figure 3. Diamondback moth cater-pillar larvae are smaller than othercaterpillar pests of cole crops; maturelarvae are green, 1⁄3 to 5⁄8 inch long,and tapered at both ends.

Figure 4. Mature cabbage looper lar-vae grow as large as 11⁄2 inches inlength and have only three pairs offleshy prolegs in the rear.

Figure 5. Green larvae of the import-ed cabbageworm can be distinguishedfrom other caterpillars by the densecoating of fine hairs that give the lar-vae a velvety appearance.

Figure 6. Cabbage webworm larvaeare 3⁄4 inch long when mature and aregray in color with five dark stripes.

Figure 7. The cross-striped cabbage-worm is easy to identify by the blackand white transverse stripes down theback.

Figure 8. Beet armyworm larvae arelight green to dark olive green and mayhave longitudinal stripes on the backor sides of the body.

Figure 9. Cutworms are dark gray-brown in color with a greasy appear-ance, and they often curl into a Cshape at rest or when disturbed.

Figure 10. Seed and root maggots arethe immature, or maggot, stages offlies that are attracted to decayingorganic matter.

Figure 11. Several aphid species, includ-ing cabbage aphids, infest cole crops.Large numbers of aphids may kill smallplants, and their feeding can distortleaves of older plants, causing leaf curl.

Figure 12. Closely related to thestinkbug, the harlequin bug is a brightlycolored, shield-shaped bug with redand black markings and piercing-suck-ing mouthparts.

Figure 13. Flea beetle adults aresmall, dark-colored beetles with en-larged hind legs that enable them tojump great distances.

Figure 14. Vegetable weevil adult

Guide to Commercial Cabbage Production 3

Soil and FertilityCabbage can be grown on a

wide range of soil types. A well-drained sandy loam soil with goodorganic content is preferred. Avoidsoils that tend to dry quickly. Adjustsoil pH to between 6.0 and 6.5.Plow under cover crops at least 1month before planting to allow suf-ficient time for the cover crop todecompose. To avoid potential soil-borne disease and nematode prob-lems, do not plant cabbage in soilsthat have produced a crop of cab-bage, broccoli, collards, or anyother cole crop in the past 2 to 3years. Crop rotation can be an ef-fective means of decreasing diseaseseverity or incidence.

Soil testing is essential for de-termining the amount of fertilizer

(besides 10-10-10) can be used tosupply equivalent amounts of nutri-ents. Fertilizer applied before plant-ing or transplanting should be wellmixed into the soil to prevent anychance of plant injury.

Variety SelectionCabbage varieties can differ in

terms of head size, density, shape(globe, round, flat round), color(green, red, blue-green), leaf tex-ture (smooth or savoyed), and mar-ket maturity as well as tolerance tobolting. Read variety descriptions inseed catalogues, variety trial re-ports, and other publications to de-termine whether a particular varietymeets all the requirements for yourgrowing area, season of produc-tion, and intended market. Most va-rieties indicate whether they aresuited to spring and/or fall produc-tion. This is an indication of howsusceptible that variety is to bolting.In Alabama, bolting tends to bemore problematic in the springwhen temperatures commonly fluc-tuate above 75°F. For a spring crop,choose a cabbage variety that isless sensitive to bolting.

Disease resistance/tolerance isalso important. The disease blackrot (described in the ControllingDiseases section) can be devastat-ing to cabbage because it can bedifficult to control. Use cabbage va-rieties that are tolerant of the dis-ease, especially for plantings thatwill be placed into fields that haveproduced cabbage or any othercole crop in the past 2 to 3 years.

Tolerance to a physiologicalcondition called tipburn is also de-sirable. Tipburn is related to a calci-um deficiency in developing tissue.The condition is favored by exces-sive or rapid growth due to overfer-tilization, or it can be caused bylow soil pH. High relative humidityalso favors the development of tip-burn. Symptoms of tipburn are notalways detectable on the exteriorsof heads (Figure 2). Often, it is notapparent until a head is cut in halfand the internal tissue is examined.

Table 1. Number of Plants Requiredat Various Spacings

Number of plants requiredper acre at two spacings

Between-row spacing 36 inches 42 inches

12 inches 14,520 12,44615 inches 11,616 9,957

between plants within a row.Another option is to use doublerows (two rows of plants withineach bed). Using double rows willincrease your yields from 30 to 50percent or more. Plants in doublerows compete better with weedsand produce a more uniform crop.

Use Table 1 to determine thenumber of plants per acre requiredat the various spacings. To deter-mine the number of plants requiredper acre for any spacing, divide43,560 (number of square feet in 1acre) by the product of the desiredspacing between plants and thespacing between the rows. For ex-ample, a 12-inch between-plantspacing on 36-inch centers wouldrequire 14,520 plants per acre: (12in. x 36 in. or 1 ft. x 3 ft. = 3 ft.2;then divide 43,560 by 3 = 14,520plants per acre). For double rows,simply double the number of plantsrequired for single-row production.

and lime required to successfullyproduce a crop of cabbage. Thebest strategy is to have a soil testperformed yearly. Timely and ap-propriate applications of fertilizercan make a significant difference inthe quality and quantity of cabbageharvested. Collect soil samples fromeach area that you intend to crop,and have a soil analysis performedon each sample. Apply recom-mended lime 2 to 3 months be-fore planting because it takes timefor lime to raise the soil pH. Failureto properly lime your soil can ulti-mately cause your crop to have amajor nutritional problem that isnot easily corrected. Often, by thetime a nutrient disorder is visible, itis too late to salvage the crop, es-pecially if that disorder has resultedfrom very low soil pH. Contactyour county Extension agent forinformation about how to collect,submit, and interpret the results ofyour soil test.

The general recommendationfor cabbage is to apply enough fer-tilizer to furnish 120 pounds eachof nitrogen (N), phosphorus(P2O5), and potassium (K2O) peracre. This can be done by applying800 pounds of 10-10-10 per acre bybroadcast or band placement meth-ods before planting. Also apply 10to 20 pounds of Borax per ton offertilizer. If boron is not appliedwith preplant fertilizer, spray 10pounds of Solubor per acre or 2quarts of N-Boron per acre directedat the base of young plants. Colecrops have a higher demand forboron than many other vegetablecrops do. A boron deficiency canmanifest itself as a condition called“hollow heart” in cabbage. Withhollow heart, the pith of the head(center) becomes cracked andbrown as the cabbage reachesmaturity.

Sidedress with 20 to 25 poundsof N per acre 2 weeks after trans-planting or 4 to 5 weeks after di-rect-seeding. Sidedress again withanother 20 to 25 pounds N per acre3 weeks later. Other fertilizer grades

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Tissue inside the head turns black,especially the tissue that surroundsthe growing point of the head.Once tipburn develops, it cannotbe reversed, and the head is un-marketable. To prevent or limit thedevelopment of tipburn, grow onlytolerant varieties and avoid exces-sive fertilization. Soil test and limewith dolomitic or calcitic lime to apH of 6.0 to 6.5. Apply calcium ifnecessary as indicated by the soiltest. Sprays containing calcium canalso be used to supply extra calci-um, especially under stressfulgrowing conditions. These sprays,however, are not a substitute forproper soil pH and an adequatesoil calcium level.

Contact your county Extensionagent for a copy of the latest edi-tion of the report entitled “FallVegetable Variety Trials” from theAlabama Agricultural ExperimentStation at Auburn University. In thereport, you will find informationabout the performance of selectedcabbages in trials at several loca-tions throughout Alabama.Although there are a large numberof commercial varieties available,grow only those that are adapted toAlabama. It is advisable to grow asmall trial plot of several varietieseach year to determine which vari-eties are best suited to your specificgrowing conditions, managementpractices, and marketing outlets.

IrrigationIrrigation is an essential ele-

ment of a successful vegetable pro-duction operation and is critical tothe consistent production of qualityproduce. Cabbage is a fast-growing,shallow-rooted crop whose rootspenetrate only 12 to 15 inches intothe soil. Although cabbage is rela-tively drought tolerant, adequatesoil moisture levels should be

maintained to maximize yields. Incabbage, the most critical periodfor irrigation is following direct-seeding or transplanting and duringhead development. Any stress relat-ed to a lack of water during theseperiods can lead to small head size(reduced yields), growth cracks, ortipburn. Any of these problems willresult in the production of poor-quality heads, reducing their mar-ketability and value.

Production on Plastic Mulch

Using polyethylene (plastic)mulch offers several advantages.Plastic mulch increases soil temper-ature, which accelerates plantgrowth and development. It alsoconserves soil moisture and re-duces several problems includingcompaction and crusting of soil,leaching of fertilizer, drowning ofcrops, evaporation of soil moisture,and competition from weeds. Atharvest, wrapper leaves are cleaner,requiring less washing, whichgreatly facilitates field packing.

Although using mulch increasesproduction costs, those costs canbe offset by earlier and larger yieldsof high-quality heads. In order tospread increased costs over twoseasons, growers can plant anothercrop (double cropping) into plasticmulch before or after the cabbage.Care must be taken throughout thegrowing season not to tear or oth-erwise damage the mulch. Double-cropping will spread your produc-tion costs over two crops, decreas-ing the risk associated with higherpreharvest costs. In the fall, grow-ers in Alabama commonly double-crop cabbage following such cropsas watermelons and tomatoes orpreceding such crops as tomatoes,bell peppers, and watermelons inthe spring. On plastic, use doublerows of cabbage plants spaced 12to 14 inches apart between rowswithin the bed. Contact your coun-ty Extension agent for more infor-mation about using plastic mulch.

Controlling Weeds,Insects, Diseases, and Other Pests

Contact your county Extensionagent or consult Extension publica-tion ANR-500A, Alabama PestManagement Handbook—Volume1, for current information on strate-gies to control pests (fungi, bacte-ria, nematodes, insects, weeds) andfor materials used to control thesepests in cabbage. Always confirmthat what you are applying willcontrol the target pest(s). If you are unsure, contact your countyExtension agent.

Since cabbage is related tobroccoli, collards, cauliflower, andother cole crops, it is a host formany of the same pests that attackthese other cole crops. Planting re-lated crops year after year in thesame area will increase pest pres-sure in that area. Eventually, youmight not be able to produce amarketable crop of cabbage. Toavoid this, rotate to crops in otherplant families (such as the Cucurbitfamily—cucumbers, watermelons;or the Solanaceaous family—toma-toes, bell peppers, eggplant).

The use of cover crops can alsobe used in a rotation. Crop rotationis one of the most effective pest-management strategies that a grow-er can use. Locate fields for cab-bage production away from areaswhere any related crops weregrown the previous season. Thelonger the rotation, the more effec-tive the pest control will be (3 to 4years is ideal).

Controlling WeedsWeed management in cole

crops in Alabama usually beginswith some form of tillage beforeseeding or transplanting to destroyemerged weeds. Nonselective her-bicides such as Gramoxone Extra(Zeneca) or Roundup Ultra(Monsanto) can be used in place oftillage to destroy emerged weeds ifthe crop is planted no-till. Most her-bicides registered for use in cole

Guide to Commercial Cabbage Production 5

crops are designed to provide con-trol of annual grasses such as annu-al bluegrass and crabgrass andsmall-seeded broadleaf weeds suchas chickweed, henbit, lambsquarter,and common purslane.

Avoid locations with heavyweed pressure, especially areaswith perennial weeds such asnutsedge. If nutsedge is a problem,consult Extension publication ANR-1073, “Nutsedge Control inCommercial Vegetables.”

Mechanical cultivation betweenrows is a valuable tool for use incole crops. Cabbage is a shallow-rooted crop, so cultivation shouldnot extend any deeper than 2 inch-es into the soil. On small areas,using organic or plastic mulch willhelp suppress many weeds. Theherbicides currently registered foruse in cabbage, broccoli, and cauli-flower are listed below. Theseproducts must be used according tolabel directions and applied withthe proper equipment calibrated toapply correct rates.

Dacthal 75W (ISK Biosciences)at 6 to 14 lb./acre. Dacthal shouldbe applied preplant-incorporated orpreemergence to the soil surfaceafter seeding or transplanting. Thisproduct requires rainfall or over-head sprinkler irrigation for activa-tion to control annual grasses andsmall-seeded broadleaf weeds.Dacthal will not control emergedweeds. Crop rotation restriction: 8months for crops not specified onthe label.

Devrinol 50DF (United Phos-phorus) at 4 lb./acre. Devrinolshould be applied preemergence tosoil after seeding or transplanting.This product requires rainfall oroverhead sprinkler irrigation for ac-tivation to control annual grassesand small-seeded broadleaf weeds.Devrinol will not control emergedweeds. Crop rotation restriction: 12months for crops not specified onthe label.

Goal 2XL (Rohm and Haas) at1 to 2 pt./acre. Goal should be ap-plied to the soil surface beforetransplanting. Transplanting shouldbe done with the least amount ofsoil disturbance possible. DO NOTuse on direct-seeded crops. Use alow rate on sandy soils. Goal con-trols small-seeded broadleaf weeds.Use with a grass herbicide to obtainadequate annual grass control.Crop rotation restriction: see label.

Prefar 4E (Gowan) at 5 to 6qt./acre. Prefar should be appliedpreplant-incorporated or preemer-gence to soil after transplanting forcontrol of annual grasses and small-seeded broadleaf weeds. Prefar willnot control emerged weeds. Irrigatewith overhead sprinklers immedi-ately after preemergence applica-tion. Crop rotation restriction: 4months for crops not specified onthe label.

Poast 1.5E (BASF) at 0.5 to 1.5pt./acre. Poast should be appliedover-the-top for control of emergedannual and perennial grasses. Poastwill not control broadleaf weeds.Two pints of crop oil concentrateper acre should be added to allPoast treatments. Poast should notbe sprayed within 30 days of har-vest. Crop rotation restriction:none.

Trifluralin 4E (several manu-facturers) at 1 to 1.5 pt./acre.Trifluralin should be applied pre-plant-incorporated before seedingor transplanting for control of an-nual grasses and small-seededbroadleaf weeds. Crop rotationrestriction: 5 months for crops notspecified on the label.

Controlling InsectsCabbage and the other cole

crops share many of the same in-sect pests. Although the informa-tion presented here was developedspecifically for cabbage, broccoli,and cauliflower, the majority willapply to all cole crops grown inAlabama.

Scouting FieldsThe most important tool in pest

management is regular (at leastweekly) scouting of fields to cor-rectly identify pests and to deter-mine if their numbers and potentialfor damage warrant treatment.Growers who monitor their fieldsare able to make treatment deci-sions based on knowledge of pestconditions, and they can avoid hav-ing to make unnecessary pesticideapplications. Most insect pestsfound on cole crops have parasiteand predator natural enemies thatare often able to keep pests belowdamaging levels. Because naturalenemies are very sensitive to syn-thetic insecticides, particularly thosewith a broad target range, it is bestto use insecticides only when nec-essary based on scouting informa-tion. When scouting plants, it is im-portant to correctly identify pestsbecause incorrect identificationmay result in false estimates of thepotential for damage or improperselection of pesticides for control.

When scouting, it is helpful todivide each field into four quad-rants. Scouting should be done in azigzag pattern across the field toensure that all quadrants of thefield are covered. Approximately 10sites should be sampled in thefield, with 5 adjacent plants sam-pled at each site for a total of 50plants per field. The plants shouldbe selected at random—do not se-lect plants because they are large orlook damaged. Sample field edgesand areas with poor stands sepa-rately; some insect infestations startat and may be limited to theseareas. At each plant, count andrecord caterpillars before samplingfor aphids or other pests. Keepwritten records of pest observa-tions. It is helpful to develop aprinted format and make copies touse on each sampling date. Keepseparate records for each insectspecies because many insecticidesare not equally effective against allspecies.

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Determining When to Treat for Insect Pests

For pest management purpos-es, plant growth can be separatedinto the following three stages: (1)seedling development, or prethin-ning stage (seed to 6 inches), (2)preheading or precupping stage(from thinning to head formation),and (3) heading or cupping stage(heads forming).

The extent of economic dam-age caused by insects depends oncrop growth stage, so treatmentthresholds change as the plantsgrow. Small seedling plants (stage1) are very susceptible to insectdamage, and large numbers of in-sects that migrate into fields can de-stroy plant stands. Plants in stage 2,between thinning and head forma-tion, can tolerate moderate insectpopulations. Because most leavesand stems grown during this timedo not go to market, moderatedamage will not cause economicloss as long as it does not stuntplant growth and delay maturity.Treatment thresholds must be low-ered during stage 3 because insectdamage or contamination duringhead formation will reduce themarket value of the crop. There-fore, when scouting for insectpests, it is important to consider theplant growth stage in determiningwhether treatments are necessary.Crop-maturity-based action thresh-olds for several insect pests havebeen developed and are listedbelow.

Applying InsecticidesAdequate spray coverage is

critical to successful pest manage-ment in cole crops because leavesgrow close together and insectsseek protected areas underneathand between leaves. Good spraycoverage is particularly importantwhen using Bacillus thuringiensis(Bt) insecticides because caterpil-lars must eat the treated foliage toingest the toxin. The advantage ofBt insecticides is that they are non-toxic to humans and most insect

natural enemies. For best results, all insecticides should be appliedusing a boom sprayer equippedwith swivel-type drop nozzlesarranged with one nozzle overeach row and adjacent nozzles ondrop tubes between plants. Thisway, the spray is directed over thetops of the plants and also outwardand upward into the plants. Thetop nozzle should be approximate-ly 9 to 12 inches from the top ofthe plant, and the drop nozzleshould be within 3 inches of theground or bed between rows. Onenozzle directly over the row is suf-ficient during the stage 1 growthphase. For complete coverage, thesprayer should be operated at 150to 250 pounds per square inch (psi)with 80 to 120 gallons of spray vol-ume per acre. Because cole cropshave a waxy layer on the leaf sur-face, a spreader-sticker productshould be included in the spraytank to inhibit the formation oflarge drops and to ensure evenwetting of the spray on the foliage.Refer to Extension publicationANR-500A, Alabama Pest Manage-ment Handbook—Volume 1, for acomplete listing of recommendedinsecticides.

Foliage-Feeding CaterpillarsDiamondback Moth Caterpillar.

Diamondback moth (DBM) has be-come a serious worldwide pest ofcole crops because it has been ableto develop resistance to insecti-cides. The caterpillar’s name comesfrom the diamond-shaped markingson the adult moth. DBM caterpillarsare most active in spring and earlysummer, producing as many as tengenerations during the growingseason. DBM larvae are smallerthan the larvae of other caterpillarpests of cole crops. Mature larvaeare green, 1⁄3 to 5⁄8 inch long, andtapered at both ends (Figure 3). Alarva wriggles violently when dis-turbed and often dangles from aleaf by a silken thread.

Larvae feed on the leaf under-sides. Small larvae do not chew

completely through the leaf, givingthe damage a “windowpane” ap-pearance. Large larvae can chewcompletely through leaves, creatingholes. Larvae may also feed on thedeveloping heads, causing headdeformation and providing entryfor disease. DBM pupae are greenand enclosed in netlike cocoons at-tached to the foliage.

Because DBM populations canincrease rapidly at temperaturesabove 80°F, at least twice-weeklyscouting is recommended. Heavyrains may reduce populations dra-matically. Bt insecticides are usuallyeffective and should be applied atthe first sign of worm activity (seetreatment thresholds below). Spraysmay need to be applied at 5-day in-tervals when populations are high.A combination of Bt and pyrethroidinsecticides (e.g., Asana, Ambush,Pounce) may be used if increasedactivity is needed. DBM pupae suf-fer natural mortality from nativeparasitoids, and parasitized pupaecan be recognized by the presenceof a broad white stripe around thepupa. Disking after harvest to de-stroy crop debris will preventbuildup of DBM and migration toplants in adjacent fields.

Cabbage Looper. The cabbagelooper (CL) is most active in earlysummer and fall. Mature larvaegrow as large as 11⁄2 inches inlength and have only three pairs offleshy prolegs in the rear (Figure4). The larvae loop their bodieswhen they move and grasp theplants tenaciously when handled.Their green color blends well withthe foliage, and their dark frass, orexcrement, is often detected beforethe larvae are seen. CL pupae aregreen and are attached to the leafundersides. They are twice as largeas DBM pupae. CL larvae chewcomplete holes in the leaves, andmore mature, larger larvae con-sume great amounts of plant mater-ial. Because large larvae are lesssusceptible to insecticides thanyoung larvae are, sprays should beapplied when larvae are still in the

Guide to Commercial Cabbage Production 7

early growth stages. Bt insecticidesare moderately to highly effectiveand may be combined withpyrethroid insecticides (e.g., Asana,Ambush, Pounce) for increased ac-tivity if needed.

Imported Cabbageworm.Imported cabbageworm (ICW)moths are white to yellowish-whitebutterflies with black spots on theirwings. Unlike nocturnal CL moths,ICW moths are often seen flyingaround plants during the day. Thegreen larvae can be distinguishedfrom other caterpillars by the densecoating of fine hairs that give thelarvae a velvety appearance (Figure5). The mature larva has a faint or-ange stripe down the back. The lar-vae chew irregular holes in theleaves, bore into heads, and conta-minate leaves and heads with fecalmaterial. Damage is similar to thatcaused by the CL. ICW is effectivelycontrolled with the same insecti-cides recommended for the DBMand CL.

Treatment Thresholds for DBM,CL, and ICW. Because these threeworm species cause similar dam-age, they should be considered to-gether when making treatment de-cisions. Because different types andsizes of worms cause varying levelsof feeding damage, their impor-tance should be weighted accord-ing to the following chart. Afterfield scouting is conducted, add thetotal number of each of the wormspecies found on all the plant sam-ples, and fill in column 2 of Table 2below.

If the average number of larvalunits exceeds the thresholds inTable 3, treatment is warranted. Ifthe number is below the specifiedthresholds, treatment is not needed.If numbers are just below or atthreshold, repeat sampling duringthe next 48 hours to determine iflarval unit numbers are increasing(treatment is needed) or decreasing(treatment not needed).

Cabbage Webworm. Cabbagewebworm larvae are 3⁄4 inch longwhen mature and gray in color

Table 2. Chart for Conversion of Caterpillar Counts to Larval Units

(1)Insect and Size (2)Total (3)Conversion (4)LarvalCounted Factor Units

Large CL ________ x 1 = _________Small CL ________ x 2⁄3 = _________Large ICW ________ x 2⁄3 = _________Small ICW ________ x 1⁄10 = _________DBM Larvae ________ x 1⁄10 = _________Multiply the numbers in column 2 by the appropriate conversion factor (column 3) tocalculate the larval units (column 4). Next, add all the larval units together, and dividethe total by the number of plants sampled to get the average number of larval units perplant.Total larval units ÷ no. plants sampled = larval units per plant_____________ ÷ _______________ = _________________

Finally, consult Table 3 to determine if treatment is necessary.

Table 3. Treatment Thresholds for DBM, CL, and ICW*

Plant Growth Stage Treatment Thresholds (avg. larvalunits/plant)

1. Seedling to 6 inches 0.502. Preheading or precupping 1.303. Early to late head or cup formation 0.50*Thresholds developed by the New York State IPM Program and validated in cabbagetrials in Alabama.

with five dark stripes (Figure 6).The head capsule is black with adistinct white V-shaped mark.Cabbage webworm is an occasion-al pest of cole crops and feeds inareas around buds. The caterpillarsproduce webbing that can protectthem against insecticide contact.Insecticides for other caterpillarswill provide control of webwormsas long as the bud areas are ade-quately covered by spray.

Cross-Striped Cabbageworm.The cross-striped cabbageworm(Figure 7) is easy to identify by theblack and white transverse stripesdown the back. It is controlled withBt and other insecticides recom-mended for caterpillar control incole crops.

Beet Armyworm. Beet army-worms may infest fall plantings ofcabbage and other cole crops. Theymay move into cole crops in largenumbers as other crops die or areharvested, so it is important to moni-tor late summer/fall plantings care-fully and to apply insecticides wheninfestations are first detected. Themoths lay egg masses on the under-sides of leaves and cover the eggswith white, fuzzy scales. The larvae

are light green to dark olive greenand may have longitudinal stripes onthe back or sides of the body (Figure8). There is a black spot above thesecond pair of true legs just behindthe head. Recommended insecticidesshould be applied if egg masses orlarvae are found on 2 to 3 percent ofthe plants.

Other Insect PestsCutworms. Cutworms are cater-

pillars that rest beneath the soilduring the day and feed at night,causing damage to stems and fo-liage. They are dark gray-brown incolor with a greasy appearance,and they often curl into a C shapeat rest or when disturbed (Figure9). Cutworm larvae overwinter infields and therefore may be presentat the time of planting, particularlyin fields with high organic matterfrom previous crop residue. Cut-worms can be detected when landis prepared for planting, and a pre-planting or at-planting soil insecti-cide can be applied if necessary. Ifcutworm damage is observed afterplanting, insecticide sprays directedto the base of the plants mayachieve some control.

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Seed and Root Maggots. Theseare the immature, or maggot, stagesof flies that are attracted to decay-ing organic matter (Figure 10). Themaggots feed on young roots andstems and may severely reduceplant stands. Damage usually oc-curs during cool, wet spring condi-tions when plants grow slowly. Thebest approach to preventing mag-got damage is to plant seed ortransplants when weather condi-tions are favorable for rapid plantgrowth. Planting when conditionsare cool and wet increases the riskof maggot damage.

Aphids. Several aphid species,including cabbage aphids (Figure11), may infest cole crops. Cool, dryweather is most favorable for aphiddevelopment. Aphids do not usuallyinfest seedlings but may build upafter thinning or transplanting havebeen done. Large numbers ofaphids may kill small plants, andtheir feeding can distort leaves ofolder plants, causing leaf curl.

Often, the most serious prob-lem associated with aphids is cont-amination. Aphid colonies in theheads of cabbage, broccoli, andcauliflower are almost impossibleto remove before marketing.Natural enemies can provide con-trol of aphids, but they usually donot build up fast enough to keepheavy aphid populations belowdamaging levels. Use of broad-spectrum insecticides likepyrethroids can increase aphidnumbers by eliminating natural en-emies; therefore, these insecticidesshould be used sparingly early inthe season and only when neces-sary to control other insect pests.

Sweetpotato or SilverleafWhitefly. Adults are tiny, wingedinsects about 1⁄16 inch long withwhite bodies and yellow heads.Although small, they are easy todetect on the undersides of leavesor when they fly off plants whendisturbed. They lay eggs on the un-dersides of the leaves where theimmobile nymphs develop. Thenymphs are scalelike in appear-

ance. Like aphids, whitefly adultsand nymphs suck plant sap withpiercing-sucking mouthparts, andthey produce sticky honeydew onleaves where they are feeding.Black sooty mold often grows onthe excreted honeydew. Insecti-cides are not highly effectiveagainst whiteflies, so prevention isthe best approach. Make sure thattransplants are free of whiteflies,and plant fields as far as possiblefrom other whitefly-infested crops.Destroy weeds and previous cropresidues that may harbor whiteflypopulations.

Harlequin Bug. This insect isclosely related to the common stinkbug. It is a brightly colored, shield-shaped bug with red and blackmarkings and piercing-suckingmouthparts (Figure 12). It feeds inthe veins of leaves, causing leavesto wilt. Harlequin bug eggs are bar-rel-shaped and laid in clusters onleaves. The eggs are white, andeach has two black bands aroundthe circumference. Treatmentthresholds developed in Georgiarecommend treatment if one bugper ten plants is found.

Flea Beetle. Flea beetles aremost common in the spring and infields that are weedy or are sur-rounded by weeds. The adults aresmall, dark-colored beetles with en-larged hind legs that enable themto jump great distances (Figure 13).They feed on the undersides ofleaves, causing numerous small,round, or irregular holes often re-ferred to as “shot-hole damage.”Flea beetles are of most concernduring the seedling stage and donot usually cause economic dam-age to mature plants.

Vegetable Weevil. The vegetableweevil adult is 1⁄4 to 3⁄8 inch longwith a stout snout (Figure 14). It isbrownish gray with two light-col-ored marks on the wing covers.Larvae are legless grubs. Adults and larvae feed on the foliage andstems of plants and cause the mostdamage when feeding on seed-lings, causing significant stand

reductions in young plantings, par-ticularly in early fall and springplantings. Treatment is recommend-ed if more than 5 percent of thestand exhibits damage.

Controlling DiseasesThere are a number of plant

diseases that can limit cabbage pro-duction in Alabama, includingblack rot, black leg, Alternaria leafspot, wirestem, and downy mildew.

Black RotBlack rot, caused by the bac-

terium Xanthomonas campestris, isa problem on cole crops worldwide.Black rot is considered to be themost important disease affectingcabbage production in Alabama andthe Southeast. It is not uncommonto lose an entire crop to black rot.

SymptomsSeedling infection first appears

as a blackening along the marginsof the cotyledons. Cotyledons shriv-el and drop off. Infected seedlingsare often stunted and yellowed andmay eventually wilt and die. Seed-ling infection can be difficult to di-agnose since only a few plants in alot may be infected.

On older plants, the disease iseasily recognized by the presenceof yellow V-shaped or U-shapedareas extending inward from themargins of the leaves (Figures 15and 16). As the disease progresses,the yellow lesions turn brown andthe tissue dies (Figure 17). Veinsdarken and the midrib of leavesturns black within the affected leafarea. This vein discoloration pro-gresses toward the base of the leaf.Eventually, the bacteria spread intothe main stem. When infectedstems are cut in cross-section, ablack vascular ring may be evidentwhere bacteria have moved intothe water-conducting vessels. Thisvascular discoloration extends fromthe stem to the upper leaves anddown into the roots. In later stagesof the disease, all central tissues ofthe main stem turn black. This

Guide to Commercial Cabbage Production 9

symptom can be confused withFusarium yellows disease; however,discoloration caused by Fusarium isdark brown rather than black.

Cabbage heads infected withblack rot often do not reach fullsize, and their lower leaves fall off.Frequently, symptoms are moresevere on one side of the head.Diseased plants may rot quickly be-fore or after harvest, owing to sec-ondary, soft-rotting bacteria. Soft-rotting bacteria commonly invadeheads of black-rot-infected plantsand turn them into slimy, foul-smelling masses of tissue (Figure18). Late infections from black rotmay simply result in leaf spots orsmaller heads.

Black rot is usually most severein low, wet areas of fields or alongwindbreaks where plants remainwet for long periods of time. Blackrot can also be seen moving downrows as the bacterium is spreadduring cultivation. However, distrib-ution of the disease often is quiteuniform across production fields.

Transmission and PersistenceThe black rot bacterium can be

carried over from year to year in oron the seeds of infected cole crophost plants, on overwintering cru-ciferous weeds, or in partially de-cayed, infected plant material in thesoil. The bacterium can persist inplant residue for 1 to 2 years or aslong as the plant debris remains in-tact. Black rot is spread on seedand seedlings, by movement ofcontaminated plant material, in irri-gation water or splashing rain, byinsects, by cultivation equipment,and by field workers. The organismcan also survive on numerousweed hosts in the mustard family,including black mustard, fieldmustard, wild turnip, wild radish,shepherdspurse, and Virginia pep-perweed.

In the spring when seedlingsemerge, bacteria are typically car-ried from diseased plant refuse toleaf edges by splashing rain.Bacteria invade young leaves

through natural openings orwounds. From the infected leaves,the bacteria move through thewater-conducting vessels to themain stem, down into the roots,and up into the leaves. Plant-to-plant infection in the field occursthrough the hydathodes at leaf mar-gins. Bacteria can also enterthrough insect feeding wounds.“Clipping” of oversized transplantswith rotary or flail mowers alsopromotes spread of the disease ifthe bacterium is present. Root in-fections can occur through woundsand are most common when infest-ed soil is saturated with water.

The disease develops bestunder warm, wet conditions.Growth of the bacterium is favoredby temperatures of 80°F to 86°F.Free moisture in the form of rain,dew, or fog is required for infectionto occur and for the disease todevelop.

ControlPurchase and plant certified,

disease-free transplants only.Always examine plants thoroughlybefore purchasing them. Plants thatare discolored, have visible lesions,or appear unhealthy should not bepurchased. Grow plants in fieldsthat have not held cole crops for atleast 3 years. Rotate with plantsfrom other plant families that arenot hosts of the disease. Plant onlyin areas that provide good soildrainage and free air movement.Provide a balanced soil fertility pro-gram based on recent soil test in-formation. Control all cruciferousweeds in and around the produc-tion field. To avoid spreading thedisease, do not work in fields whenplants are wet. Control cabbageroot maggots, cutworms, cabbage-worms, and other insects, usingrecommended control practices.When possible, clean up and burnor cleanly plow down all crop de-bris immediately after harvest.Removing plant residue from thefield surface will greatly reduce thebacterium’s ability to survive the

winter. A copper-containing prod-uct such as Kocide will reducedamage from black rot. Begin ap-plying the material when weatherconditions favor disease develop-ment. Apply the material at 7- to10-day intervals. Be aware that cop-per-containing products may causeplant injury.

Black LegBlack leg, caused by the fungus

Phoma lingam, can cause seriouslosses in cabbage production. Blackleg and black rot are the two mostserious diseases of cabbage.

SymptomsSymptoms of black leg are usu-

ally first seen in the field as anoval, sunken, light brown canker,often with a black or purple marginnear the base of the stem. Thecanker enlarges until the stem isgirdled and the plant wilts and dies.Foliar symptoms first appear aspale, irregular-shaped spots onleaves. These spots gradually en-large, becoming circular with graycenters. Small, black, pepperlikespots (pycnidia) can be seen withinthe leaf spots. These are the spore-producing structures of the fungus,which can also be seen within stemcankers. Severely infected plantsare stunted. Infected plants eventu-ally wilt and then turn a dull blue-red color. With black leg, it is notuncommon for plants to suddenlyfall over due to the deterioration ofthe stem (Figure 19).

Transmission and PersistenceThe fungus can survive in

plant residue for 2 to 3 years. Itcan also be carried on seed. Plantsare often infected in the seedbed,where splashing water spreads thespores of the fungus from oneplant to another. Secondaryspread of the disease may occurduring the transplanting/pullingoperation. The fungus can also bespread by splashing rain, by work-ers, and on equipment in thefield. The disease is more severeunder wet conditions.

10 Alabama Cooperative Extension System

ControlPurchase only transplants certi-

fied to be free of black leg. Nevergrow cabbage in a field where acole crop was grown in the past 3years. Remove plant debris follow-ing a season when the disease waspresent. Fungicide seed treatmentsand soil fumigation or solarizationhave been shown to be effective incontrolling black leg.

Alternaria Leaf SpotAlternaria leaf spot is caused by

the fungus Alternaria brassicae.The disease can cause severe dam-age to cabbage if left uncontrolled.

SymptomsThe initial symptoms are small,

circular, dark spots on the surfacesof older leaves. As the spots en-large, concentric rings developwithin the lesions (Figure 20). A le-sion is often surrounded by a yel-low halo. The tan-colored centersof spots may eventually drop out,producing a shot-hole appearance,or under wet conditions may be-come covered with a black mass offungal spores (Figure 21). If left un-controlled, the disease can defoliatea plant. In storage, spots enlargeand soft-rotting bacteria may enterthrough these lesions.

Transmission and PersistenceThe disease can overwinter on

crop debris. Cruciferous weeds mayalso harbor the fungus. Spores ofAlternaria can be spread by windand in water. The disease is mostdamaging under wet, warm condi-tions (68°F to 81°F).

ControlNever grow cabbage in a field

where a cole crop was grown inthe past 3 years. Remove plant de-bris following a season when thedisease was present. Plant disease-free transplants. Begin a fungicidespray program at the first sign ofthe disease, and continue at 7- to10-day intervals with a protective-type fungicide (fungicides with theactive ingredient chlorothalonil[Bravo] or maneb [Manex, Maneb80]).

WirestemWirestem, caused by the fun-

gus Rhizoctonia solani, can be aproblem in transplant beds as wellas in the field. Early, fall-plantedcabbage is more vulnerable to thedisease.

SymptomsPlants infected with wirestem

often have a reddish-brown discol-oration to their stem near the soilline; the discolored area often ap-pears severely constricted. Plantsmay be bent or twisted at this pointbut do not break, hence the name“wirestem.” Affected plants that sur-vive are weak and produce smallheads.

Transmission and PersistenceThe fungus is present in all

soils but is more common in soilwith infected plant debris that hasnot decomposed. Prolonged, overlymoist soil favors development ofthe disease. The amount of wire-stem is greatly influenced by therecent cropping history.

ControlNever grow cabbage in a field

where a cole crop was grown inthe past 3 years. Remove plant de-bris following a season when thedisease was present. Soil fumiga-tion and careful watering may re-duce damage from this disease.The fungicide Terraclor can beused in the transplant water forcontrol of wirestem.

Downy MildewDowny mildew is caused by

the fungus Peronospora parasitica.The disease can enter a field on in-fected transplants or wind-blownspores. Plants can be infected any-time during the growing season.

SymptomsIn moist weather, a white,

fluffy, fungal growth developsmostly on the undersides of infect-ed leaves. With time, yellow to tanspots develop on the correspond-ing upper leaf surface. Infectedleaves on young plants may drop,and plants may die. Infected leaveson older plants usually remain at-tached. On older leaves, the infect-ed areas turn tan in color and pa-pery in texture. A mass of grayspores can be seen on the under-sides of infected leaves. Downymildew can predispose infectedplants to bacterial soft rot.

Transmission and PersistenceThe fungus overwinters on

seed, in cruciferous weeds, andpossibly in the soil. Heavy fogs,light rains, prolonged dews, andnight temperatures between 46°Fand 61°F with day temperaturesbelow 75°F greatly favor this path-ogen. Spores of the fungus floatlong distances in cool, moist air.

ControlEradicate cruciferous weeds to

eliminate potential overwinteringdisease inoculum. Do not use over-head irrigation. The fungicidesAlliette, Aliette/Maneb 2+2, andRidomil/Bravo 81 are labeled foruse on cabbage for control ofdowny mildew.

Guide to Commercial Cabbage Production 11

Figure 19. Root and stem tissue dam-age and deterioration caused by blackleg infection

Figure 20. Lesion caused byAlternaria leaf spot. Note the en-larged, concentric rings that developwithin the lesions.

Figure 21. Black mass of fungalspores on lesion produced byAlternaria leaf spot

Figure 15. Close-up of lesions oncabbage leaves caused by black rot.Note the V- or U-shaped areas ex-tending inward from the leaf margins.

Figure 16. Production field with cab-bage infected by black rot

Figure 17. Close-up of cabbage leafwith characteristic symptoms of blackrot. Lesions have turned brown, andtissue has begun to die.

Figure 18. Area of cabbage field in-fected with black rot where soft-rot-ting bacteria have invaded the heads

ANR-1135

Harvesting and Storing Cabbage

Yields will vary with the seasonof production, variety, and produc-tion system used. With proper man-agement, cabbage can produce 10to 12 tons per acre (400 to 500 50-pound crates or bags). Growers inAlabama have produced upwardsof 16 to 20 tons per acre. Generally,most markets prefer heads that av-erage 2 to 21⁄2 pounds. Some vari-eties of cabbage mature uniformly,requiring one to two harvests.Others can require three or morepickings to complete harvesting.

When harvesting, cut stemsclose to the ground near the baseof the head. Be sure that heads arewell formed and firm (see Figure1). Typically, outer wrapper leavesare removed. Once cut, removecabbage from direct sunlight be-cause cabbage wilts quickly whenexposed to sunlight. Wilting resultsfrom a loss of water from the head.Cool cabbage to 40°F before ship-ping it. This will increase shelf lifeand reduce the development of rotdiseases. In cold storage, cabbagecan be stored at 32°F with 98 to100 percent relative humidity for 5to 6 months.

Acknowledgement: Some ofthe information on insect pest biol-ogy and treatment thresholds wasdeveloped by the New York StateIPM Program and the GeorgiaCooperative Extension Service andused with permission. We sincerelythank Dr. David Adams, GeorgiaCooperative Extension Service, forpermission to use some insect im-ages originally published inGeorgia Cooperative ExtensionService Bulletin 1067, Leafy Greensand Cabbage Production.

J.M. Kemble, Extension Horticulturist, Assistant Professor, Horticulture, G.W. Zehnder, ExtensionEntomologist, Professor, Entomology, E.J. Sikora, Extension Plant Pathologist, Associate Professor,Plant Pathology, and M.G. Patterson, Extension Weed Specialist, Professor, Agronomy and Soils, allat Auburn University Use pesticides only according to the directions on the label. Follow all directions, precautions, and restrictions that are list-ed. Do not use pesticides on plants that are not listed on the label.

The pesticide rates in this publication are recommended only if they are registered with the Environmental ProtectionAgency and the Alabama Department of Agriculture and Industries. If a registration is changed or cancelled, the rate listedhere is no longer recommended. Before you apply any pesticide, check with your county Extension agent for the latest in-formation.

Trade names are used only to give specific information. The Alabama Cooperative Extension System does not endorse orguarantee any product and does not recommend one product instead of another that might be similar.

For more information, call your county Extension office. Look in your telephone directory under your county’s name tofind the number.

Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, andother related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension System(Alabama A&M University and Auburn University) offers educational programs, materials, and equal opportunity employmentto all people without regard to race, color, national origin, religion, sex, age, veteran status, or disability.

CP, 3M76, New July 1999, ANR-1135