A3785

K.A. DelahautA.C. Newenhouse

Growingonions, garlic,leeks, and other alliumsin WisconsinA guide for fresh-market growers

ContentsPlant description, 1

Site selection, 4

Cultivar selection, 4

Planting, transplanting, and culture, 5

Soils and nutrient management, 8

Irrigation, 10

Harvest, handling, and storage, 10

Insect management, 12

Disease management, 16

Weed management, 18

Additional reading, 19

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).

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1

Onions and garlic offer plentyof marketing opportunitiessince these crops can be

sold at different stages of growth, theirharvest dates are flexible, they can be

stored, and value-added productssuch as onion and garlic braids

can bring more sales. Onionsand garlic are staple ingredi-

ents in cooking and their healthbenefits have been touted for

centuries. If you grow different types of alliums(members of the onion family) such as sweet onions,storage onions, green onions, or scallions, you canextend your harvest season from early spring throughlate fall. For example, you can plant onion or scallionseeds in late summer for a green onion crop in thefall, or to transplant the sweet bulbing onions the fol-lowing April for harvest when mature in June.

Plant descriptionOnions, garlic, leeks, chives, shallots, and othermembers of the onion family are commonly grown infresh market gardens. Plants in the family Alliaceae(previously Amaryllidaceae) are native to central Asiaand derive their characteristic flavor from the enzymealliinase that acts on sulfur compounds. Onions andother alliums contain simple sugars such as glucose,fructose, and sucrose.

Onions have been used for thousands of years. Theyhave been identified in drawings on Egyptian tombsdating back to 2800 B.C. Onions continue to beprized for their medicinal value derived from sulfurcompounds which have antimicrobial and antifungalproperties, and for their high anti-platelet activitywhich thins the blood if onions are eaten raw.Historically, onions have also been used to controldysentery. Garlic has been used in middle Asia,Egypt, and the Mediterranean as far back as 2000B.C. Leeks are thought to have originated in theeastern Mediterranean and records of leek cultivationdate back to biblical times.

All plants in the Allium family are herbaceous, cool-season, biennial vegetables that are grown asannuals. Root systems are fibrous and shallow withall roots arising from a basal plate, including a fewlateral roots. Members of this plant group have fleshybasal leaves that can be tubular or slightly flattened.

Bulbs form from enlarged leaf bases called scales. Acombination of day length and temperature triggersbulb formation. High temperatures favor bulbingonce a critical day length has been reached. Sinceyield is determined by the number of leaves presentat bulb initiation, early planting ensures the maximumnumber of leaves and the largest bulbs.

When temperatures fall below 50°F, stems begin toelongate and flowering will occur. Long days alonewill not induce flowering, but will speed up stemelongation. Flowers are radially symmetrical and areperfect (have both male and female flower parts).Individual flowers are borne in spherical umbelscomprised of as many as 1000 flowers. Alliumflowers are pollinated by insects.

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escription

Vidalia onionsOnions grown on soils low in sulfurhave low pungency. In Vidalia,Georgia, soils are naturally leached ofsulfur and therefore the sweet types ofonions grown there (Granex types)have low pungency. By federal law,only Granex types of onions grown inVidalia, Georgia can be called “Vidaliaonions.” Sweet Spanish onions grownin the north can be just as sweet.

2OnionsOnions (Allium cepa var. cepa) are classified aseither short-day, intermediate, or long-day cultivarsaccording to the number of hours of light required toinitiate bulb formation. Long-day onions grown undershort-day conditions form leaves but not bulbs.Short-day onions grown under long-day conditionsform small bulbs early. Long-day onions are grown inWisconsin, requiring daylengths of 14 hours or longerto initiate bulbs. Long-day onions can be grown forimmediate consumption or long-term storage.Typically, onions described as sweet should be eatensoon after harvest and onions described as dry canwithstand prolonged storage. Short-day onions suchas Bermuda onions cannot be grown in Wisconsin orareas at more than 30° latitude. Long-day onions areusually more pungent than their short-day relatives.Other factors affecting pungency include characteris-tics of the specific cultivar along with environmentalconditions such as temperature, soil pH, andmoisture extremes. Environmental conditions canalso affect foliage size and color, bulb formation andsize, bulb splitting, scale color and thickness, seedstalk formation, and storage quality. Onions may bespherical, flattened, or conical in shape and haveskin colors ranging from white to yellow or brown,and red to purple. Bulb shape and size may also berelated to the length of the growing period with rapidgrowth resulting in elongated bulbs while longgrowing periods produce larger bulbs. Multiple bulbsoccur when lateral buds sprout in the leaf axils.

Green onions are actually immature true onions. Theyare harvested before bulbing has begun.

Scallions (sometimes called bunching onions) neverform a bulb despite environmental triggers that willinitiate bulb formation in other cultivars.

Japanese bunching onions (Allium fistulosum) aresimilar to scallions in that they do not form bulbs.They are very hardy and can be seeded in latesummer to be overwintered and harvested in spring.

Multiplier onions belong to the Allium cepa var. aggre-gatum group and form 4–5 bulbs enclosed within asingle leaf sheath. The bulbs of multiplier onions havea similar use in cooking as shallots while the greentops can be eaten like green onions.

Shallots (Allium cepa var. ascalonicum) resemblesmall true onions but develop a small cluster of bulbsrather than a single bulb. They are harvested whenthe bulbs are about 2 inches in diameter and areprized for their delicate, subtle flavor.

Pearl onions are not true onions but a member of thespecies Allium ampeloprasum which contains theleeks. They are short-day onions grown under long-day conditions so they only form a single storageleaf.

Summer mini onions or cipollini (Allium cepa) are mildand sweet small early onions that are planted in earlyspring. They’re harvested when approximately golfball sized, 60 days later.

Table 1. Nutritional information for onion, garlic, and leeks

Nutrition facts Onions Garlic Leeks

Serving size 1 cup, cooked 3 cloves, raw 1⁄4 cup, cooked

Calories 92 13 8

Protein 2.8 gm 0.5 gm 0.2 gm

Carbohydrates 21 gm 3 gm 2 gm

Fat 0.4 gm 0 gm 0 gm

Vitamins and Vitamin C—11 mg Potassium—36 mg Potassium—23 mgminerals Folate—31mg Phytochemical— Anticarcinogen—

Potassium—348 mg allicin diallyl sulfide

3GarlicGarlic (Allium sativum var. sativum) is a cool-season,hardy perennial made up of multiple cloves. Of allalliums, garlic prefers warmer conditions for optimumgrowth. Each clove is comprised of one papery leafand a second, thickened storage leaf which makesup most of the clove. Individual cloves arise fromaxillary bulbs. Unlike the hollow, tubular leaves ofonion, garlic leaves are solid, flattened, and folded.The leaves of garlic also do not serve as storageorgans as do onion leaves. Garlic rarely producesflowers, but it forms bulbils or small bulbs at the topof a flower stem called a scape.

There are two types of garlic cultivars: hardneck andsoftneck. Hardneck cultivars are more cold hardyand have a milder flavor than softneck and are themost sought-after gourmet varieties. They arederived from wild garlic and will, under the right con-ditions, produce a flower stalk with fertile flowers. Theflower stalk hardens to make a stiff “neck.” Softneckgarlic produces higher yields, has better storagequalities, and a stronger flavor than hardneckedgarlic but doesn’t do as well in Wisconsin’s climate.Cold winters and heavy rains before harvest lowerthe quality of softneck garlic. Softneck garlic doesnot produce flowers and must be propagated vege-tatively. The stems of softneck garlic can be braided.

Elephant garlicElephant garlic (Allium ampeloprasum var. holmense)is a form of leek that produces a mild-flavored bulbresembling a giant garlic.

LeeksLeeks (Allium ampeloprasum var. porrum) are robust,winter-hardy biennials that do not form a hard bulblike onions or garlic. Instead, they are grown for theirlong, thick white stem. Leaves are solid, flat, andfolded like the leaves of garlic. The leaves arise fromthe basal stem and are borne opposite each otherwith new leaves arising above the previous one.Leeks are sweeter than onions and have a creamytexture when cooked. They are used to flavor soupsand stews.

ChivesChives (Allium schoenoprasum) are a perennialgrown primarily as an herb. The plant forms anherbaceous mound that produces flowers annually.Chives never develop usable bulbs.

Wild leek or rampWild leeks, or ramps, (Allium tricoccum) are found inWisconsin’s rich, moist woods, in the eastern moun-tains of North America, as far west as Minnesota, andnorth to Canada. Ramps are perennial plants withtwo to three lily-like leaves 6–18 inches tall. Theleaves are scented like onion or leek and the bulbhas a sweet flavor that is similar to but less potentthan garlic. Flowers are white to creamy yellow andbloom from June to July after leaves wither. NativeAmericans used ramps in cooking, and their sweetflavor continues to be prized by consumers andrestaurant cooks.

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escription

Site selectionOnions and their relatives require full sun and growbest on muck soils (containing at least 20% organicmatter), and irrigated sandy soils. They tend toperform poorly on heavy clay soils. Soil pH should be6.0–6.8. Some vegetables, such as beets or colecrops, reduce soil pH and should not be plantedimmediately before alliums in a rotation unless youadjust the soil pH prior to planting. Alliums areshallow rooted so they tend to dry out quickly andare also sensitive to waterlogged conditions. Choosewell-drained soils with a good moisture-holdingcapacity unless you plan to irrigate during dryweather.

Prepare new sites at least one season beforeplanting alliums. Green manure worked into the soilincreases the amount of organic matter therebyimproving the quality of the crop grown. As with allroot crops, the soil should be free of weeds androcks before planting.

Grow leeks on deep soils to allow for the trenchesnecessary to blanch them.

Cultivar selectionRefer to table 2 for a list of some suggested cultivarsfor Wisconsin.

OnionsOnions are bred for flavor, sugar content, storagequality, size, shape, color, adaptability to differentgrowing conditions, and early maturity. Breeders alsoselect for disease resistance and yield.

GarlicGarlic is bred for winter hardiness, productivity,flavor, disease resistance, and nutraceutical qualitiessuch as blood thinners and other beneficial healtheffects.

LeeksLeek breeders select for size and shape of the stalk,hardiness, disease resistance, and early maturity.

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Note: Choose cultivarsaccording to your own situa-tion and needs. Considerwhat your market demands,the length of your growingseason, your soil, pests,diseases, irrigation, cultivarsother growers like, and culti-vars you personally like.When trying a new cultivar,do not use it exclusively.Grow new trials next to oldstandbys so you maycompare the characteristicsobjectively.

Onion

White

Evergreen White Bunching

Super Star (Spanish)

Sweet Spanish

Walla Walla (sweet)

Yellow

Candy (sweet)

Copra (storage)

First Edition (storage)

Yellow SweetSpanish

Red

Mars (storage)

Mercury (storage)

Garlic

Softneck

California White

Inchelium Red

New York White

Polish White

Silver Rose

Hardneck

Chesnok Red

German Extra Hardy

Killarney Red

Music

Russian Red

Siberian

Spanish Roja

Leek

American Flag

Giant Musselburg

King Richard

Otina

Pancho

Table 2. Recommended cultivars

5Planting, transplanting,and cultureOnions may be grown from seed, sets, or transplants.Precision seeding has made controlled plant spacingeasier and has improved the survival rate of pre-ger-minated seed. Since most onions require a longgrowing season, growers usually raise onions fromtransplants rather than direct seeding. You can startyour own seedlings or purchase them from a dealer.Planting onion sets is not recommended for market-quality onions. Sets are the second year’s growth ofstorage varieties or multiplier onions and thereforetend to be less sweet than other onions. In addition,they may bolt or go to seed early.

Starting seedsPlant onion seeds in a greenhouse or under lightsindoors in late January or February, 10–12 weeksbefore the last frost date in your area (see figure 1).Use a sterile potting mix that contains compost, peat,or sphagnum to retain moisture; vermiculite or perlitefor aeration; and mineral and nutrient sources toencourage growth after the first roots form. Preventbacterial and fungal infections by sterilizing trans-plant trays in a 10% bleach solution before you plant.Fill flats or cell trays with media or make individualsoil blocks with a soil blocker. Plant seeds 1⁄4-inchdeep either in rows in flats, or with 3–5 seeds per cellor soil block. Label trays with cultivar and plantingdate. Keep media moist but not wet. Maintain soiltemperature at 70–72˚F using a heating mat or cableuntil seedlings emerge, in 6–12 days. Keep tempera-tures in the greenhouse at 60–65˚F during the day,

site selection �cultivars

�planting

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

and 55–60˚F at night. If you are starting onionseedlings indoors under fluorescent lights, provide atleast 10 hours of light a day. Ideally, the seedlingsshould be 1⁄4-inch thick at transplanting. You mayneed to experiment with seed spacing and plantingdates to find the best scheme for your situation.

A week before transplanting to the field, move plantsinto a cold frame where lower temperatures willharden them off. Reduce water and withhold fertilizerwhile the plants are in the cold frame to help accli-mate them to field conditions.

Soil preparationAlliums, with their shallow root systems, grow best inwell-prepared soil. The seedbed or transplant bedshould have loose, crumbly soil that is free of stones,clods, or debris. In soils with a naturally low organicmatter content, add composts and other organicmaterials. Alliums compete poorly with weeds, so it isimportant to control weeds before planting. Workbeds 7–8 inches deep, being sure to bury surfaceorganic matter to prevent attracting the onionmaggot. Raised beds are an alternative to the con-ventional field planting method. They improve soildrainage and allow access to the crop withoutcausing soil compaction. Raised beds are typically4–5 feet wide and 100 feet long. The width is deter-mined by the type of equipment used and by thecrop. Leave a 1-foot aisle on either side of each bedto accommodate foot traffic.

Direct seeding To direct seed onions or leeks, sow seeds 1⁄4–3⁄4inches deep, 8–12 seeds per row foot. Thin onions to3–4 inches between plants and leeks to 4–6 inches.(Garlic is planted as cloves, not seeds.) Onion seedis often graded and pelleted to make germinationmore uniform. You can also seed onions in the fieldfor transplanting later. Plant seeds at four to five timesthe rate for direct seeding and transplant seedlingswhen they are 1⁄4-inch in diameter. Given good condi-tions, seeds germinate 6–12 days after planting. Theoptimum temperature range for germination isbetween 70–85˚F. As allium seeds germinate theembryonic root and shoot are pushed out of the seedcoat but the tip of the cotyledon remains in the seedproducing a bent seedling. This unusual-lookingseedling is referred to as the knee stage.

TransplantingTransplant onions in mid-April, once frost is out of theground and approximately 4 weeks before the lastfrost date. If you are growing onions from purchasedtransplants, place roots in a shallow pan of waterimmediately upon arrival, and plant them within a dayor two. Plant transplants 1 inch deep and 4 inchesapart. At transplanting, clip off tops to 5 inches toprevent drying out while the transplant’s root systembecomes established. Water onion transplants imme-diately after planting. Even though onions appear topush up out of the ground as they grow, they do notneed soil hilled up around them.

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Planting time Plants or seeds Seed Spacing (inches)b

Days Estimated in southern WIa needed for depth Between Between to first yield (lb/ft

Vegetable Indoors Outdoors 100 ft of row (inches) rows plants harvestc

of row)d

Onion Feb. 15 April 15 1⁄2 oz 1⁄4–3⁄4 16–24 3–4 110–120 200 lb

Garlic — Oct. 15 400–600 cloves 2–3 18–30 4–6 60–90 40–70 lb

Leek Feb. 15 April 15 1⁄4–1⁄2 oz 1⁄4–3⁄4 16–24 4–6 120–150 150 stalksaPlant about 1 week later along the lower lake shore and in the central part of state and about 2 weeks later in northerncounties.

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

dEstimated yields under less than ideal growing conditions; actual yields will vary widely with weather, soil fertility andcultural practices.

Table 3. Planting guide

7If you are growing onions from sets, plant the sets1–2 inches deep and 3–4 inches apart in the row. Toreduce the likelihood of bolting, use sets that are1⁄4 inch or smaller in diameter.

Onion cultureEach onion cultivar has a specific day length require-ment that triggers the plant to form a bulb. The rateof growth and ultimate size of the bulb are influencedby temperature, nutrition, soil moisture, and competi-tion. Until the plant receives the critical amount ofday length, it grows new leaves without forming abulb. These can be harvested as green bunchingonions.

Onions and other alliums bolt when plants aresubject to temperatures between 40–50°F for 1–2months. Onions grown from sets are prone to boltingif exposed to prolonged cool temperatures in thespring.

Garlic culture Since cultivated garlic rarely produces fertile flowers,garlic is propagated vegetatively by planting clovessaved from the previous crop. Larger cloves producelarger bulbs. Bulbils form at the top of a stem calleda scape, but plants propagated from these bulbilswill be too small to be marketable.

The best time to plant garlic cloves is in the fall, 6–8weeks before the ground freezes. This allows thecloves time to grow roots under cool conditions andbecome established before winter. Garlic should notbe planted in the spring since warm temperaturesand increasing day length will stimulate prematurebulb formation. You will need 100 pounds of garlic for1000 square feet if you plant the cloves 4 inchesapart in the bed. To prevent disease, wait to dividethe bulbs until just before planting. Plant cloves withtheir points up, 2–3 inches deep and 4–6 inchesapart. Garlic is commonly planted in double or triplerows in beds that are 2–3 feet apart. If planted tooshallow, shoots may start to grow in fall. These tendershoots detract from root production and will be killedin the winter. Once the soil has frozen, mulch theplants with a layer of 4–6 inches of weed-free strawto prevent soil heaving. By spring the mulch will have

compacted to about 1 inch. Remove the mulch inearly spring to help warm up the soil and speedgrowth, or leave it in place to add organic matter tothe soil. Garlic requires a moderate amount ofnitrogen for optimum growth. On soils with more than20% organic matter, apply 35 lb nitrogen/acre. Onsandy soils with less than 2% organic matter, apply60 lb nitrogen/acre. Garlic is best able to use thenitrogen when it’s applied in two or three smalleramounts. If applying twice, make the first at plantingand the second about 2 weeks after emergence inspring. For three applications, apply a third of thenitrogen at planting, at emergence in spring, andagain 1 month later. Avoid applying nitrogen within60 days before harvest to help the plants die backproperly.

In early summer, when the scape on hardneck garlichas formed a circle, remove it and its bulbils (ortopsets) so the bulb grows to an adequate size of8–10 cloves. The bulbils and scapes have a mildflavor and can be marketed for cooking.

You can also grow green garlic, which is garlic that isharvested before it forms bulbs. Green garlic can beproduced from small cloves, dense plant popula-tions, or thinnings. It has a milder flavor than bulbgarlic and can be eaten raw like green onions orchopped and cooked to add flavor to meat or veg-etable dishes.

Leek cultureLeeks are more cold tolerant than onions and garlicwith the best temperatures for leek developmentbetween 68° and 78˚F. Leeks have site requirementssimilar to those of onions and garlic but prefer wetterconditions. Leeks are usually propagated by seedgrown indoors and then transplanted into the fieldwhen weather conditions permit. Direct seeding isnot practical for leeks because of the slow rate ofseed germination. Plant leek seeds in flats 1⁄4 inchapart and 1⁄4 inch deep in February–March.Transplant to 1 inch apart when the plants are bigenough to handle. You can also seed directly into acoldframe. In mid- to late April, transplants should beplanted 4–6 inches apart within the row and 18 inchesbetween rows, in a furrow or individual holes 5–6inches deep, letting at least 1–2 inches of leaves

planting

, transplanting

, and culture

extend above the soil surface. Instead of firming upthe soil near the base of the transplants, let rain andirrigation help fill in the hole over time. Systematicallyburying the lower portion of the plant creates thecharacteristic blanched or whitened leek stem. Thelonger the blanched stem, the higher the quality. Toblanch stems, wait until leeks put out new stronggrowth. Then start gradually filling in the furrow withsoil to blanch 5–6 inches of the stem. You can use acultivator or hoe to hill up soil around the base of theplant two or three times during the growing season.Do not bury the place where the leaf attaches to thestem. Leeks grow slowly and can require 120–150days before reaching maturity.

Elephant garlic cultureElephant garlic is slightly less hardy than regulargarlic. Plant and mulch elephant garlic in the fall asyou would regular garlic, but plant cloves 2–3 inchesdeep and 6–8 inches apart. Hill up the plants with2–3 inches of soil. Elephant garlic will produce leavesbefore the ground freezes. The next spring, break offany flower buds. Elephant garlic requires approxi-mately three times more nitrogen than regular garlic.

Wild leek or ramp cultureCollecting ramps from the wild may decimate localnative populations. If you harvest from the wild,remove no more than 5–10% of the plants in eachplot to maintain the patch. When growing your ownramps, plant enough so that you harvest only 1⁄7 to 1⁄5of the plot each year. Choose a shady, moist site thatis well drained. The soil should have a high level oforganic matter. The site could be under naturalshade from trees such as sugar maple, birch, beech,linden, hickory, and oak, or from a shade structure.Ramps are perennial plants that grow new leaves inMarch through April. These leaves die back in June,the plant produces a flower stalk, and the flowerblooms in early summer. Seeds develop in latesummer and need a warm, moist period followed bya cold period to break dormancy. If they don’treceive these conditions, it may take 18 months forthem to germinate. Growing ramps from seed takes5–7 years to get the stand to maturity.

You can also grow ramps from transplants or bulbs.Plant bulbs in March and transplants in March–April.Plant bulbs 4–6 inches apart and 3 inches deep,leaving the tip of the bulb above the soil surface.Plant transplants to the same depth they weregrowing. Cover ramp seeds, bulbs, or transplantswith 2–3 inches of hardwood leaf mulch.

Soils and nutrientmanagementCompared to other vegetables, onions and otheralliums are shallow, heavy feeders. Obtain a soil testfor available nutrients before planting a field for thefirst time. You’ll need to test the soil again at leastonce every 3 years to keep your fertility managementprogram current. For information on how to collectgood samples and where to get them analyzed, seeExtension publication Sampling Soils for Testing(A2100).

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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 thesource.

9soils and

nutrient manag

ement

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 history andplanned use of the field. If you plan to apply supple-mental fertilizer to alliums, band the application ratherthan broadcasting it since the roots don’t extend farfrom the plant. Two or three small nitrogen applicationsare more effective than one large application.

Soil pHSoil pH for onions should be between 6.5 and 8.0 onmineral soils or 5.8 on peat. For garlic, the soil pHshould be between 6.0 and 7.0. The soil pH for leeksshould be 6.0–8.0.

Fertilizer needsPlants take up nitrogen as nitrate (NO3

–) orammonium (NH4

+), phosphorus as phosphate(P2O5), and potassium as potash (K2O). These nutri-ents can come from organic or inorganic sources.Soil microbes break down organic matter freeing upchemical nutrients needed by plants. Organic fertiliz-ers can also improve soil tilth and health. Inorganicfertilizers can be used to quickly supply nutrients toplants.

Organic fertilizers can come from a variety ofsources such as manures, compost, fish meal, andbone meal. Each material contains varying amountsof specific nutrients. Table 4 lists organic fertilizersand the amounts of nutrients in each. For more infor-mation on this subject, refer to Extension publicationOrganic Soil Conditioners (A2305).

Alliums require relatively high levels of phosphorusand potassium compared to other vegetables. (Seetable 5 for recommended annual amounts.) Theyalso have a high requirement for copper, man-ganese, zinc, and (on muck soils) for molybdenum.

Manganese deficiency results in a gradual, interveinalchlorosis, stunting, and twisting of the top growth ononions and other alliums. Plants also exhibit delayedbulbing and thick necks. Manganese deficiency ismost common on muck soils with a high pH.

Zinc deficiency is commonly encountered in bothsands and muck soils because of the naturally lowlevels of this micronutrient in the soil. Symptoms ofzinc deficiency include overall stunting of the plant, atwisting and outward bending of the leaves, and afaint yellowing of the tissue between the leaf veins onthe younger leaves.

Table 5. Annual nitrogen, phosphate (P2O5), and potash (K2O) recommendations

Nitrogen Phosphate and potash

Organic Amount to applya

matter Amount to apply Yield goal P2O5 K2O

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

Onions <2.0 150 5.5 400–600 60 2.2 130 4.78

2.0–9.9 140 5.25

10–20 130 4.78

>20 120 4.5

aAmounts of P2O5 and K2O are for optimum soil test levels. Apply half the given rate if the soil test is high and omit if the soil test is excessivelyhigh. If soil test is low or very low, increase rates according to the soil test recommendations.

10IrrigationOnions with their shallow root systems need frequentwatering to keep the top 3–4 inches of soil moist.Roots grow from a flat “stem plate” on the bottom ofthe bulb, and until the onions form bulbs, this stemplate should not be allowed to dry out. On sandysoils, you may need to water daily. Once the plantsstart to bulb, they’ll need an inch of water a week. Athorough soaking once a week will produce astronger root system than frequent, light waterings.Cut back on irrigation 1–2 weeks before harvest.

Garlic requires consistent soil moisture during thebulbing period (April – June). Cut back on irrigation3–4 weeks before harvest (mid-July to mid-August) toprevent bulb rot.

Leeks require less water than onions. After establish-ment they should only be irrigated during prolongeddrought conditions.

If leaves begin to wilt mid-day, plants are moisturestressed. Plants that wilt intermittently producesmaller yields. Plants that wilt frequently or that havebeen allowed to wilt too long will often die due to per-manent cell damage.

Both drip and overhead sprinkler irrigation systemsare effective. These systems include trickle tape,solid set, and traveler hose wheel.

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.

Harvest, handling, and storage

OnionsHarvest fresh onions when 15–25% of the tops havefallen over. Storage onions should be harvestedwhen 50–80% of the tops have fallen over. If storageonions are harvested earlier, they are more likely torot during storage. Onions harvested after more than80% of the tops have dried down will be more sus-ceptible to scale infection during storage. Undercutthe roots with a blade or in small quantities by handwith a spade or spading fork. Even though onionsfeel solid, they bruise easily and should be handledcarefully to avoid damaging the bulb which can leadto storage rots.

USDA size categories for U.S. No. 1 onionsDescription: Onions must be mature,firm, well-shaped, free from decay anddamage, and at least 40% must begreater than 11/2 inches in diameter.

Sizes (diameter):

Small = 1–21⁄4 inches

Medium = 2–31⁄4 inches

Large or jumbo = >3 inches

Colossal = >33⁄4 inches

11Green onions can be pulled any time the tops are atleast 6 inches tall and 1⁄2–1 inches in diameter. Two tothree weeks before harvest, hill up approximately 2inches of soil around the base of the stems to blanchthem. At harvest, remove the discolored outer skin,trim the leaves, and bunch with a rubber bandaccording to the size bunch common in your market(usually 5–7 onions). Wearing a supply of rubberbands around your wrist speeds bunching. Keepgreen onions cool to maintain quality.

After harvest, storage onions should be cured at tem-peratures of 85–90˚F under low humidity for severaldays to one week. Curing and drying promotesdormancy, enhances the development of well-colored scales and prevents inoculation by diseaseorganisms. Leave the dry, outer scales on the bulbsthroughout the curing process. If curing onionsoutdoors, protect them from moisture and direct sun.You can put onions on screens on warm, dry dayswith an adequate breeze for good air circulation.Place them in a shady location away from rainfall andheavy dews. Properly cured onions have dry outerscales and a dry neck. Onions can be stored for upto 6 months at temperatures of 32˚F and humiditylevels of 60–70%. Onions may sprout in storage iftemperatures exceed 40˚F.

GarlicHarvest garlic when two-thirds of the tops are dryand the leaves collapse. Pull a few bulbs nearharvest to determine exactly when to harvest thecrop. Later harvest gives bigger bulbs, but the skinmight split and lower bulb quality. Bulbs can rot andindividual cloves may split off if garlic is left in thefield after it matures. Harvest garlic on a warm dryday to prevent soil from adhering to the bulbs,making them difficult to clean. Garlic can be dug witha spading fork in small plantings or with the sameharvesting equipment used for onions in larger plant-ings. The roots are then undercut with a lifter beforebeing pulled. Never pull garlic bulbs without firstloosening the soil with a shovel or spading fork.Remove excess soil from the bulbs in the field. If youintend to market garlic braids, leave the tops on andbraid the garlic immediately after harvest. Then curethe braids as you would bulbs.

To cure garlic, either windrow bulbs in the field forseveral days, crate them in standard plastic venti-lated containers and keep them in the field with goodair circulation, or lay them out in a shady spot withgood air flow. Garlic should be cured for 30 daysafter harvest. During this period, the bulbs will loseup to half their weight and will improve in flavor.Before storing or marketing garlic, peel off the outerone or two layers of skin, trim roots to 1 inch, and trimthe tops to 11⁄2–2 inches (unless braided). Garlic maybe stored with the dried tops removed, trimmed,intact, or braided.

irrigation

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Harvesting&packing tips

When harvesting onions, garlic, and leeks,change your position often to minimize stressand fatigue to your body. You might wearkneepads, or sit on a small cart. Use gardencarts and wagons as much as possible tominimize lifting and hand carrying heavyproduce. Standardized vented plastic contain-ers that stack are easy to load and unload,and clean.

With a smooth level floor in the packing area, apalletized packing and storage system can bedesigned to fit small-scale operations (smallpallets moved with a hand-pulled pallet jack)or large operations (pallets moved by forklift).Heavy boxes of produce can be moved fromone area to another on roller tables.

Lay out your washing and packing area tominimize stooping, lifting, and carrying. Set upscreen tables so you can work at table height.Ideally, tables could be adjusted to matcheach worker, so that work is performed at aheight between wrist and elbow. For moreinformation on tools and methods to improvework efficiency visit the University of WisconsinHealthy Farmers, Healthy Profits website atbse.wisc.edu/hfhp/.

12Garlic can be stored for up to 6 months at 32˚F andhumidity levels of 60–70%. Storage temperaturesabove 40˚F will cause garlic cloves to sprout andrelative humidity levels over 70% initiates root devel-opment and mold.

LeeksUnlike onions and garlic which are harvested whenthey’re dormant, leeks are harvested while they’re stillactively growing. When mature, leeks are typically11⁄4–3 inches thick, depending on the cultivar. If youheavily mulch leeks to keep the ground fromfreezing, you can extend your harvest season. Digunder the leeks to cut the extensive root systembefore pulling out plants. After harvest, trim roots andgreen leaves, and wash. You can harvest leek greensand immature stems all season. Leeks can be storedfor up to 2 months at 32˚F and 95% relative humidity.

Elephant garlicDig elephant garlic bulbs when all the leaves showsome yellowing, but before the entire top has dried.Elephant garlic bulbs are fragile. They bruise easilyand their thin papery outer covering separates easily.Brush soil away from bulbs being careful not toknock them together as you dislodge soil. Braid ortrim the leaves, cut off roots, and dry and cure thebulbs for about 6 weeks. Elephant garlic is oftenpacked for sale as individual bulbs in net bags.

Wild leek or rampsHarvest ramps when leaves are 12–18 inches tall.When harvesting, be careful not to damage thebulbs, and keep them cool and moist when digging.Trim rootlets, wash bulbs, pack them in waxed card-board boxes and store them in a cooler.

Insect managementAster leafhopper

Description: The aster leafhopper is aserious pest of onions because ittransmits the aster yellows pathogen.Adult aster leafhoppers are olive-green, wedge-shaped, and about 1⁄5-

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. They are carriednorth on warm, southerly winds. Large influxes mayoccur in June and early July as local populationsdevelop. Adult females lay eggs in the leaves of sus-ceptible 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 a plantdiseased with aster yellows, it ingests the pathogen.When the leafhopper moves to another plant to feed,it transmits the pathogen in its saliva. In onions,disease symptoms appear about one month later.

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).

13Bulbs infected with aster yellows show a generalchlorosis, stunting, and twisting of the stems andleaves. Bulbs infected with aster yellows dry poorly.

Management: Aster leafhoppers may be effectivelycontrolled by excluding them from the onion plantingusing floating row covers. Row covers should be inplace from the time the onions emerge or are trans-planted until 30 days before harvest. Drape thecovers over the crop or support it using wire hoops.Hold the material in place by burying the edges or byusing reebar or rough lumber to weigh it down.Completely seal all four edges to the ground.

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 onions are transplanted. Place the cards justabove the crop a few rows in from the outer fieldedge. Begin scouting weekly when you find leafhop-pers on the cards. Use a sweep net to take 25sweeps per site, and sample two sites per acre.Each spring, the University of Wisconsin-Extensioncollects samples of migrating leafhoppers and deter-mines the percentage that are infective. For currentinformation, contact your county Extension office. Ifthe percent of infectivity is not known, use 2.5% forthe following calculations. To decide whether treat-ment is necessary, multiply the number of leafhop-pers per 100 sweeps by the percent infectivity of themigrant populations. Treat when an index of 200 isreached. Continue treating until 30 days beforeharvest.

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.

Black cutwormDescription:Cutworms arethe larvae of noc-turnal greymoths. Cutwormsare activefeeders on young

foliage and stems and will cut off many youngseedlings in an evening. The large (11⁄2–2 inches),fleshy larvae curl up into a tight C-shape when dis-turbed.

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.

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. Shake every plant along a5-foot length of row in two adjacent rows into thefurrow and count the larvae on the soil surface. Spottreat if you find two or more larvae per foot of row.

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14Onion maggot

Description: Adult onionmaggots are slender, gray,large-winged, bristly fliesthat resemble houseflies

but are only 1⁄4-inch long. While at rest, their wingsoverlap their bodies. The maggots are approximately1-inch long, cream-colored, and legless with asharply pointed head end.

Life cycle: Onion maggots overwinter as pupae in thesoil or in onion cull piles. In mid-May, adults emergefrom the soil and lay eggs on the soil surface at thebase of onion, garlic, leek, chive, or shallot plants.When the larvae emerge, they crawl beneath the leafsheath and enter the bulb. The onion maggotpupates in the soil and the next generation appears3–4 weeks later.

There are three generations of onion maggots peryear. The first is often the largest and mostdamaging. The third generation attacks onions inmid-August shortly before harvest. Damage at thistime can lead to storage rot as onion maggots intro-duce bacteria into wounds caused by their feeding.

Damage, symptoms: Onion maggot larvae feed on thehypocotyl (below ground) tissue of seedlings, result-ing in various types of damage. Larval feeding maykill seedlings; therefore, poor plant stands mayindicate an onion maggot problem. In larger plants,larvae may tunnel into bulbs, causing plants tobecome limp and yellow. Onion maggot feeding canintroduce soft rot bacteria into the plant.

Management: Once damage has been detected, it istoo late to attempt control. Therefore, action thresh-olds for foliar insecticide applications are based onthe emergence of adults. Peak emergence of eachgeneration can be forecasted using degree-dayaccumulations (for a discussion of degree days, seesidebar). Begin degree day calculations when theground thaws in the spring. Use a base temperatureof 40°F. The three generations of adults emerge whendegree day totals reach 680DD40 (spring), 1950DD40(summer), and 3230DD40 (fall), respectively.

Effective onion maggot control programs shouldinclude the following elements to reduce populations,avoid insecticide resistance and achieve control.

1) Rotate onion crops whenever possible to provideat least 1⁄4 mile between new seedlings andprevious crops or cull piles. This may not alwaysbe possible on smaller farms.

2) Destroy crop debris and remove culls from thefield to reduce numbers of overwintering onionmaggot populations.

3) Transplant onions 1 week before flies areexpected to emerge.

If damage from the previous year’s crop exceeded5–10%, preventative soil insecticide applications arerecommended to control the first-generation larvae.

Onion thripsDescription: Adult onion thrips aretiny pale yellow or brown insectsabout 1⁄12-inch long. Their wingshave no veins and are fringed withlong hairs. Nymphs resemble adultsexcept that they are smaller andlack wings.

Life cycle: Adults and nymphs overwinter on plants,debris, and along weedy field edges. Females canreproduce without mating and lay eggs beneath theleaf’s surface. Eggs hatch after 5–10 days andnymphs are fully grown within 15–30 days. One totwo weeks after hatching, the nymphs move into thesoil to complete development. During this period,they do not feed. After the fourth molt, adult femalethrips return to the plant. Thrips produce about five toeight generations per year. Hot, dry weather favorsthrips outbreaks.

Damage, symptoms: Onion thrips damage plants pri-marily by their rasping and feeding which produceswhitish blotches on leaves and decreased pollen set.Both adults and larvae cause damage that appearsas a silvery streaking on the leaves. As time passes,affected areas become dry and yellow. Heavy infes-tations can cause onion leaf tips to turn brown.Severe damage causes bulbs to become distorted orundersized.

Management: Thrips should be controlled early,before they become protected by plant tissue. Due totheir small size and reclusive habits, onion thrips aredifficult to monitor and control. No treatment thresh-olds have been established for onions. Yellow orwhite sticky traps may be used along field edges tomonitor the initial migration of thrips into a field.Cleaning plant debris from the field and the sur-rounding area may aid in controlling thrips. Ingeneral, onion cultivars with an open type of growth,circular leaf structure, and glossy foliage suffer lessdamage than cultivars with leaf sheaths tight to thestem. Red onions are particularly susceptible toattack while sweet Spanish onions are more resistant.

Because of thrips’ protected location in the plant,control through the use of insecticides is difficult.Foliar insecticides should be applied in sufficientwater with a spray additive to achieve penetrationinto the plant.

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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

Disease management

Botrytis leaf blight and neck rotHosts and severity: Botrytis leaf blight is a destructivedisease that kills onion foliage so rapidly that it isoften referred to as “blast.” All cultivated onions aresusceptible to botrytis leaf blight. Botrytis neck rotalso originates in the field but symptoms don’tappear until the onions are in storage. White onionsare more susceptible than red or yellow varieties andleeks, shallots, and garlic are also susceptible tobotrytis neck rot.

Disease cycle: The fungi that cause leaf blight andneck rot overwinter in the soil on onion crop residuesor as sclerotia. In moist weather, the sclerotia germi-nate and produce conidia (airborne spores) whichare disseminated by wind and splashing water.These spores lodge on wet foliage and enter theplant through wounds. Onions are highly susceptibleto leaf blight during the early stages of bulbing andozone injury may aggravate leaf blight damage. Inthe case of botrytis neck blight, the fungus generallyenters after harvest through succulent tops that werenot properly dried.

Symptoms: Symptoms of botrytis leaf blight firstappear as tiny, oval, whitish or yellowish spots on theoldest leaves. If affected leaves are cut, you willnotice that the lesions extend through the thicknessof the leaf blade.

Infected plants show little or no evidence of botrytisneck rot prior to harvest, but the disease becomesobvious after onions are topped and have beenstored for a few days. Scales around the neck beginto soften and this softening progresses toward thebase of the bulb. Infected tissue takes on a sunken,brownish, water-soaked appearance with a definitemargin between healthy and diseased tissue. On redand yellow onions the pigment of diseased tissue isdestroyed.

Management: To prevent problems with botrytis leafblight, plant healthy seeds or sets in well-drained soilin areas with good air circulation. Remove weedsand destroy infected plant debris after harvest.Practice a 2-year crop rotation to avoid otherdiseases that might predispose the plants to botrytisinfection.

Onion varieties that mature readily so neck tissuesdry before storage will help to reduce the incidenceof botrytis neck rot. You can reduce plant susceptibil-ity by not applying fertilizer late in the season or pro-viding excessive irrigation when tops are drying.Harvest onions when fully mature after tops are dry.Cut tops close (1⁄2 inch from the top of the bulb) anddry stubs before storing.

Downy mildewHosts and severity: Downy mildew is a cool-weatherproblem that affects all types of onions, garlic, leeks,chives, and shallots. There are several strains of thefungus, each strain causing infection only on aspecific crop with no cross infection occurring.Under cool, moist conditions, downy mildew can bequite destructive.

Disease cycle: The fungus overwinters as thick-walledresting spores in diseased plant residue. When con-ditions are favorable, spores are produced that arecarried by air to healthy plants. Heavy fogs, persis-tent dews, and drizzling rains favor infection. Plantsmay be infected at any stage of development.

Symptoms: Downy mildew causes onion leaves tobecome blighted and die prematurely. Infectedplants produce undersized, immature bulbs that areoften attacked by other organisms after harvest.Downy mildew may produce local infections on onionleaves or the disease may become systemic withinthe plant with the older, outer leaves becominginfected first. Local infections produce lesions on theleaves and stalks that are pale green, oval toelongate, and slightly sunken. In moist weather, afuzzy violet growth develops over the entire leafsurface. As the disease progresses, entire leavesbecome pale green and finally yellow. Plants that areinfected systemically are stunted with pale greenleaves.

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Management: Prevention is best achieved by plantingdisease-free seed or sets in well-drained soil andspacing them far enough apart to promote good aircirculation. Avoid overcrowding and excessivenitrogen fertilization. Practice a 3-year crop rotationout of onions.

To prevent downy mildew, seed is usually grown inarid, western states where risk of downy mildew isnegligible. If saving your own seed however, seedshould be treated in a hot water bath. The tempera-ture of the water is critical—variation by as little asone degree will cause the seed to die or allow thepathogen to remain viable. Place the seed in a meshbag and dip the bag into water heated to 122°F for25 minutes. Transfer the bag to cold water immedi-ately to cool the seed. There will be some reductionin the germination rate of treated seed; you may wishto sow additional seed to compensate.

Onion smutHosts and severity: Onion smut is a serious and wide-spread disease of onions, leeks, and shallots.Infected plants either die or remain vegetative for theentire growing season.

Disease cycle: The fungus survives in the soil formany years even without a susceptible host. Whenonions are planted in an infested field, the sporesgerminate and infect seedlings and new transplants.

Symptoms: Onions are only susceptible to smut whilesmall; older plants become resistant. The firstsymptom of infection appears as a brown to black,elongated blister on the cotyledons and young leaves.A single lesion may cover an entire leaf and cause itto curl downward. Most infected seedlings die within3–5 weeks after germination. Plants are usually stuntedand may die slowly. If plants survive, the diseasebecomes systemic and infected plants remain vege-tative throughout the growing season. If bulbs doform, they become covered with black lesions andare open to attack by secondary organisms.

Management: To prevent onion smut, plant disease-free transplants that have passed the susceptibleperiod. Practice crop rotations to prevent inoculumbuildup in the soil.

Purple blotchHosts and severity: Purple blotch causes onions tobecome blighted and die prematurely. This diseaseaffects onions, garlic, and leeks.

Disease cycle: The purple blotch fungus overwinterson plant debris. With warm, wet weather in thespring, the fungus produces spores that infectleaves, stems and flowers of susceptible hosts. Rainor persistent moisture is necessary for infection.

Symptoms: Purple blotch first appears as small,brown, water-soaked areas on onion leaves, flowerstalks, and flowers. The enlarging spots develop lightand dark purple zones that become somewhatsunken. The border of the lesion is reddish or purplewith a yellow halo. If conditions are favorable,affected leaves and stems may turn yellow, dropover, and die within several weeks after the firstlesions appear. Onion bulbs may be attackedthrough the neck or through wounds in the bulbscales at harvest or later while in storage. Diseasedbulb tissue gradually dries out and becomes papery.

Management: Practice a 4-year crop rotation in fieldsfree of weeds and plant debris. Plant healthy seedsor sets in well-drained soil where air circulation isgood. Avoid overcrowding plants and excessivenitrogen fertilization.

Soft rotHosts and severity: Bacterial soft rot is a disease thataffects many vegetables. It can be a particularlyserious post-harvest disease if alliums are storedimproperly.

Disease cycle: The bacteria often enter susceptibleplants that are already weakened by other disease-causing organisms or they may enter through freshwounds. Onion maggots are particularly effective atspreading this disease. The gnawing action of themaggots keep the tissue freshly wounded and pre-disposed to soft rot. The maggots ingest the bacteriawhich remain in their bodies until they becomeadults. The adult flies carry the bacteria to new loca-tions and lay contaminated eggs. The bacteria arealso spread by tools, clothing, decayed plant tissue,rain, and running water.

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Symptoms: Onion bulbs may be infected in the field,but the disease often goes unnoticed until afterharvest. Bacterial soft rot usually starts at the neck ofthe bulb, and progresses downward along one ormore scales. At first the tissue is water-soaked. Laterit disintegrates into a soft, slimy mess. The decaydoes not spread easily from scale to scale. One ortwo scales may be completely rotted while theremainder are sound. Gently squeezing diseasedbulbs releases a foul-smelling watery fluid.

Management: The first step in controlling soft rot is tocontrol other diseases and avoid injury to the plants.This includes controllling insects such as the onionmaggot that wound plants and transmit the bacteria.

Allow the crop to mature completely before harvest-ing. The tops should be dried out as much aspossible after lifting and before topping. Mechanicaltoppers should be designed to minimize bruising. Atall stages of harvest and storage, onions should behandled carefully to avoid bruising. Cure bulbs thor-oughly before storage so that the outer scales andneck tissues are completely dry. And finally, removebulbs that show any sign of disease or injury beforestorage.

Weed managementWeed management is essential for crops to producemaximum yields. Weeds compete with crop plantsfor sunlight, water, nutrients, and space. Beforeplanting, reduce perennial weed populations bysmothering them 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.Preemergent herbicides may be used to clean upany annual weeds present in the field at the time ofplanting.

Non-chemical weed control in onions, garlic, andleeks is often difficult because of the relatively smallcanopy produced by these crops as compared withbean, tomatoes, or vine crops. Repeated cultivationsare often necessary to reduce weed competition inroot crop plantings. Sometimes hand cultivation orhand weeding is necessary.

Chemical weed control in onions is based on thetype of soil on which the crop is grown—muck vs.mineral soil—because the species of key weeds willdiffer as will the selection of available herbicides.

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

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Additional reading

CultureDirect 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.

Growing for Market Newsletter. Fairplain Publications,P.O. Box 3747, Lawrence, Kansas 66046. 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.

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.

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: AnIntroduction to Beneficial Natural Enemies and TheirUse in Pest Management (NCR481). Daniel L. Mahrand Nino 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. Second edition. MaryLouise 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 Onions, Garlic, Leeks, and Other Alliums 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.