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A Plain Language Guide
GrowingFresh Market
Onions,Garlic, and
Leeks
A. C. Newenhouse
�The Wisconsin Farm Center has more informationabout services to help beginning farmers. To find this information on the internet look under the heading Farming and Agriculture athttp://datcp.state.wi.us/.
Your local county Extension office also has moreinformation for fresh market farmers. Go to http://www.csrees.usda.gov/Extension/. Click on your state and then your county to findthe Extension office near you.
Plant Description ..............................................................................1
Onions ......................................................................................................................2Garlic ........................................................................................................................4Elephant Garlic ........................................................................................................4Leeks ........................................................................................................................5Chives ......................................................................................................................5Wild leek or Ramp ....................................................................................................6
Site Selection ....................................................................................6
Variety Selection................................................................................7
Planting and Care ..............................................................................8
Starting Seeds ..........................................................................................................9Soil preparation ......................................................................................................10Raised Beds............................................................................................................11Seeding in the field ................................................................................................11Transplanting ..........................................................................................................11Onion growth ..........................................................................................................12Garlic growth ..........................................................................................................12Elephant garlic growth ............................................................................................14Leek growth ............................................................................................................14Wild leek or ramp growth ........................................................................................15
Soils and Nutrient Management ....................................................16
Soil pH ....................................................................................................................16Fertilizer needs ......................................................................................................17
Irrigation ..........................................................................................18
Harvest, Handling, and Storage......................................................19
Onions ....................................................................................................................19Garlic ......................................................................................................................20Elephant garlic ........................................................................................................21Leeks ......................................................................................................................21Wild leek or ramps ..................................................................................................21
Preventing Stress on Your Body ....................................................22
Weed Management ..........................................................................23
Pest and Disease Management........................................................25
Botrytis leaf blight....................................................................................................26Botrytis neck rot ......................................................................................................26Downy mildew ........................................................................................................26
Indexi
Onion smut..............................................................................................................28Purple blotch ..........................................................................................................29Soft rot ....................................................................................................................29
Insect Management..........................................................................30
Aster leafhopper......................................................................................................30Black cutworm ........................................................................................................32Onion maggot ........................................................................................................32Onion thrips ............................................................................................................33
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Onions, garlic, and leek are goodcrops to grow for the farmers marketbecause you can sell them at differentstages of growth, their harvest datesare flexible, and you can store them.You can also make products such asgarlic braids to add value to your crop.Onions and garlic are basic cookingingredients and are healthy to eat. Ifyou grow different types of onionssuch as sweet onions, fall greenonions, and storage onions, you canharvest from early spring through latefall.
Plant Description
Onions, garlic, leeks, chives, andshallots are all members of the Alliumor onion family. These plants arenative to central Asia. The typicalonion or garlic flavor comes from anenzyme that acts with sulfur in the soiland makes sulfur compounds in theplant. These sulfur compounds areanti-microbial and anti-fungal and giveonions medicinal value. Eating rawonions helps thin the blood.
Onions, garlic, and leeks have beenused in cooking for at least 4000years in middle Asia, Egypt, and theMediterranean. Drawings of onionshave been found on tombs in Egyptfrom 2800 BC. Leeks are native to theeastern Mediterranean.
Most plants in the Allium family(alliums) are cool season biennials.Biennial plants produce leaves thefirst year and flowers the second year.They live only two years. Farmersgrow alliums as annual vegetableswithout letting them produce flowers.Alliums have shallow fibrous rootsthat grow down from a plate at thebase of the plant. Allium leaves arethick and fleshy. Leaves grow out fromthe base of the plant. Leaves can beshaped like a tube or be slightly flat.
Allium plants form bulbs. The scalesthat make bulbs are actually the thickpart at the base of each leaf. Plantsform bulbs when they have the rightday length and temperature. Whenthe plant has grown until the right day
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length, then high temperature willmake it start to form a bulb. Plantswith more leaves at that time form abigger bulb and produce higher yield.Plant early to get the most leaves andlargest bulbs.
When temperatures fall below 50°F,stems get longer and floweringbegins. Flowers have both male andfemale flower parts and are pollinatedby insects. The flower is shaped like aball or an “umbel” and is made up ofmany individual flowers together.
Onions
Onion varieties (Allium cepa var cepa)are either short day, intermediate, orlong day depending on the number ofhours of light they need to startforming bulbs. If you grow long-day
onions under short day conditions youwill get leaves but not bulbs. If yougrow short-day onions under long-dayconditions you will get small bulbsthat start to form early. Farmers in theupper Midwest usually grow long-dayonions. Long-day onions need at least14 hours of daylength before theystart to form bulbs.
Short day onions such as Bermudaonions won’t grow in areas at morethan 30° latitude.
You can grow long day onions to eatfresh or to store and keep for a longtime. Onions that are called “sweet”are usually grown to eat fresh.Onions that are called “dry” canusually be stored for a long time.Long-day onions usually have sharperflavor than short-day onions. Somefactors change the sharpness of anonion’s flavor. These factors arevariety, temperature, soil pH, and soilmoisture.
Onions can be round, slightly flat, orcone-shaped. Onion skin can bewhite, yellow, brown, red, or purple.Onion skin is used to dye cloth. Ifonions grow quickly in a short timetheir bulbs can become longer. Ifonions grow slowly over a long timetheir bulbs are larger. If side bulbssprout from inside the base of severalleaves then you will see many smallerbulbs form.
Green onions (Allium cepa var cepa)are immature onions that you harvestbefore the bulb forms.
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Onion flower - ball
Onion flower - umbel
Dr. Michael Havey, haveylab.hort.wisc.edu
© Smithsonian Institution - W.S. Justice
Scallions or “bunching onions”(Allium cepa var cepa) are varietiesthat will never form a bulb. Even if theconditions are right for other varietiesto form a bulb, scallion varieties willnot make a bulb.
Japanese bunching onions (Alliumfistulosum) do not form bulbs. Theyare similar to scallions. Japanesebunching onions are very hardy. Youcan plant them by seed in latesummer and they will overwinter.Harvest them in spring.
Multiplier onions (Allium cepa varaggregatum) form 4-5 bulbs insideeach leaf sheath. The sheath is thepart of the leaf that forms at the baseof the leaf around the stem. Eat thegreen tops raw like green onions anduse the bulbs in cooking.
Shallots (Allium cepa var.ascalonicum) look like onions but theyform a cluster of small bulbs insteadof one single bulb. Shallots have adelicate flavor. Harvest shallots whenthey are about 2 inches across.
Pearl onions are either true onions(Allium cepa) or a variety of Alliumampeloprasum. They are short-dayplants grown under long dayconditions close together in the rowso that they form tiny bulbs. Pearlonions are often pickled.
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Green onions
Pearl onions
Shallots
Summer mini onions or cipollini(Allium cepa) are small, flat earlyonions planted in early spring.Harvest them after 60 days when theyare 1 ½ - 2 inches across. Summermini-onions are mild and sweet.
Garlic
Garlic (Allium sativum var sativum) isa cool season perennial plant madeup of many cloves. Each clove hasone papery leaf and a second, thickstorage leaf that forms the clove.Plants can produce 4-40 cloves at thebase of a stalk. Garlic leaves are long,flat and folded. The flower stem of agarlic plant is called a scape. Small
bulbs (bulbils) can form at the top ofthe flower stem.
There are two kinds of garlic varieties:hardneck and softneck. Hardneckgarlic is more cold hardy and has amilder flavor than softneck. Hardneckgarlic makes a flower stalk. Thisflower stalk dries to form a stiff “neck”for the garlic. Most farmers in theMidwest grow hardneck garlic. Somesoftneck varieties also grow well inthe Midwest. Softneck garlic storesbetter than hardneck. You can braidthe stems of softneck garlic to hang itfor drying. Some softneck garlicvarieties will form a flower stalk if theygrow in the right conditions.
Elephant Garlic
Elephant garlic (Alliumampelosprasum var. holmense) is aform of leek that grows into a bulbthat looks like garlic. Elephant garlichas a mild flavor.
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Garlic
Summer mini onions or cipollini
Leeks
Leeks (Allium ampelosprasum var.porrum) are very hardy biennial plantsthat grow long, thick white stems. Theleaves are solid, flat, and folded likegarlic leaves. Leeks do not grow intobulbs. Leaves grow from the base ofthe plant. They form opposite eachother on the stem. New leaves growabove the old. Leeks are sweeter thanonions. Cooked leeks have creamytexture. Use leeks to flavor soup andstew.
Chives
Chives (Allium schoenoprasum) areperennial plants that grow in a moundas an herb. Chive leaves are used incooking. They have mild flavor. Thechive plant does not form large bulbs.Chives flower every year.
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Leeks
Chives
Wild leek or Ramp
Wild leeks, or ramps, (Alliumtricoccum) are native perennial plantsthat you can find in the woods of theMidwest. They grow in the moist forestfloor of northern US and Canada asfar west as Minnesota. Ramps havetwo-three leaves 6-18 inches tall.Ramp leaves look like lily leaves.Ramp leaves smell like onion or leek.Bulbs smell like mild, sweet garlic.Flowers are white to creamy yellowand bloom from June to July after theleaves start to die. Native Americansused ramps in cooking. Many chefslike the sweet flavor of ramps.
Site Selection
Onions and their relatives are calledalliums. They grow best in full sun.Alliums like well drained soil with highorganic matter; (at least 20%). Thistype of soil is sometimes called ‘muck’soil. Alliums also grow well on sandysoils if they are watered. Alliums donot grow well on heavy clay soils.They also cannot grow in soil thatstays wet. Alliums have shallow rootsand plants dry out quickly. If you donot have irrigation for your alliums,choose soil that is well drained andholds moisture.
Soil pH should be 6.0-6.8. Do notplant onions or their relatives rightafter beets or cole crops (broccoli,cabbage, etc.) in the same fieldbecause those crops lower the pH toomuch for onions.
One season before you plant alliums,plant cover crops in the field. Workthem into the soil to add organicmatter. These types of crops aresometimes called “green manurecrops” . Cover crops such asbuckwheat, rye, and mustards workwell as green manure for the soil.Remove weeds and rocks from thefield as much as you can beforeplanting onions and their relatives.
Grow leeks on deep soil so that youcan cover them to whiten the stalks.
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Wild leek or Ramp
Variety Selection
Choose varieties of onions and theirrelatives that suit market gardening inthe Midwest. Look for varieties thatresist disease, tolerate heat, havegood flavor, store well, and are readyto harvest early. When you choosegarlic and leak varieties, also look forones that are winter hardy. If you try anew variety, plant it next to the varietythat you normally grow so you cancompare the two. Table A lists somevarieties that usually grow well in theupper Midwest.
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Table A. Onion, Garlic,
and Leek Varieties
Variety
Onion
White Evergreen White Bunching
Super Star (Spanish)
Sweet Spanish
Walla Walla (sweet)
Yellow Candy (sweet)
Copra (storage)
First edition (storage)
Yellow Sweet Spanish
Red Mars (storage)
Mercury (storage)
Garlic
Softneck California White
Inchelium Red
New York White
Polish White
Hardneck Chesnok Red
German Extra Hardy
Killarney Red
Music
Russian Red
Siberian
Spanish Roja
Leek
American Flag
Giant Musselburg
King Richard
Otina
Pancho
Planting and Care
You can grow onions from seed,“sets”, or transplants. Since mostonions need a long growing season,most farmers usually plant transplantsinstead of planting onion seeds in thefield. You can start your own seedlingsor buy them
from a dealer. Do not grow onionsfrom “sets” if you plan to sell onions atthe market. Sets are the secondyear’s growth of storage or multiplieronion varieties. Onions grown fromsets are not as sweet as the onionsyou grow from transplants. Also, setscan go to seed (“bolt”) early.
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April 26 - May 2
May 3 - 9
May 10 - 16
May 17 - 23
May 24 - 30
May 31- June 6
September 13 - 19
September 20 - 26
September 27 - October 3
October 4 - 10
October 11-17
October 18 - 24
Frost dates maps
Last spring killing frost First fall killing frost
Starting Seeds
Plant onion seeds in a greenhouse orunder lights indoors 10-12 weeksbefore the last frost date in your area.Usually in the upper Midwest thisoccurs in late January or February. Ifyou start onions indoors underfluorescent lights, give them at least10 hours of light a day.
You can buy or mix your own sterilepotting mix. The mix should includecompost, peat, or sphagnum to holdmoisture; vermiculite or perlite foraeration; and mineral and nutrientsources to feed the new plants afterthe first roots form. Add water to makethe mix moist before you fill thetransplanting trays.
Farmers plant onion seeds indoorsinto either cell packs or trays. It is agood idea to sterilize transplant traysin a 10% bleach solution before youplant. This will prevent bacteria andfungi from infecting the youngseedlings.
✤ Fill the plastic or styrofoam celltrays with potting soil, or makeindividual blocks with a soilblocker. Cells or soil blocks assmall as ¾ inch diameter are fine.
✤ Plant seeds ¼ inch deep. Eitherplant them in rows in trays or plant2-5 seeds per cell or soil block.
✤ Label the trays with variety andplanting date.
✤ Keep soil moist but not wet.
✤ Use a heating mat or cable underthe trays to keep the soil warm to70-72°F until the seedlings sprout.You should see seedlingssprouting in 6-12 days.
✤ The temperature in thegreenhouse should be 60-65°Fduring the day.
✤ The temperature in thegreenhouse should be 55-60°Fduring the night.
✤ As leaves grow, clip them down to3-4 inches to help them growsturdy plants.
✤ At transplanting, the seedlingsshould be ¼ inch in diameter.
✤ One week before transplanting outto the field, harden off the plantsby putting them outside for a fewhours each day during thewarmest time of the day, or moveplants into a cold frame. Thesection on season extensiondescribes a cold frame.
✤ Give the plants less water and nofertilizer while they are hardeningoff.
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Table B gives the amount of seed youwill need, how deep to plant seed,how far apart to plant, when to plant,days to first harvest, and yield.
Soil preparation
Alliums have shallow root systemsand grow best in soil that is loose,crumbly, and does not contain stonesor clods. If your soil has little organicmatter, add compost. See theprevious section on green manurecrops you can grow to build theorganic matter in your soil.
It is important to control weeds beforeyou plant. You can use thesemethods:
✤ Pull weeds by hand.
✤ Smother weeds with a cover crop(such as buckwheat).
✤ Cover the soil with black plastic toheat it and keep out light.
✤ Use weed killer sprays (herbicidesprays).
For more information on weed controlread the section on weedmanagement on page 23.
Work beds 7-8 inches deep topromote good rooting. If leaves,stems or other organic matter fromplants lie on the soil surface theymight attract the onion maggot. Buryorganic matter to reduce the onionmaggot population. Never work wetsoil because this can cause soilcompaction. Compacted soils arehard and do not get enough air.Compacted soils prevent oxygen andwater from reaching roots, and plantsdo not grow as well or produce asmuch.
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Table B. Planting Guide
Planting time insouthern WIa
Plants orseeds
neededfor 100 ft
of row
Seeddepth
(inches)Spacing (inches)b
Days tofirst
harvestc
Estimatedyield
(lb/ft ofrow)d
Vegetable Indoors OutdoorsBetween
rowsBetween
plants
Onion Feb. 15 15-Apr ½ oz ¼- ¾ 16-24 3-4 110-120 200 lb
Garlic - Oct.15400-600cloves
2-3 18-30 4-6 60-90 40-70 lb
Leek Feb. 15 15-Apr ¼- ½ oz ¼- ¾ 16-24 4-6 120-150 150 stalks
a Plant about 1 week later along the lower lake shore and about 2 weeks later in the north.
b If you use a plate-type seeder, the plate will make the spacing between plants.
c Varieties are ready to harvest at different times; plant different types to have a longer growing season.d Estimated yields under less than ideal growing conditions; actual yields will vary widely with weather,soil fertility and cultural practices.
Raised Beds
You can use raised beds to improvesoil drainage and prevent compaction.Raised beds are usually 4-5 feet wideand 100 feet long. Leave a 1-foot aisleon either side of each bed for a path.
Seeding in the field
Some farmers do not planttransplants but seed directly into thefield. If you plant seeds in the field youwill need to thin the plants. Somecompanies sell pelleted seeds thatare coated and rolled to make themuniform and easier to handle,especially for growers who plant witha precision seeder. Precision seedingis done with special planters anduniformly sized seeds, and is done ina way that you do not have to go backand thin the plants. Many differenttypes of planters are available suchas the gravity-feed cone seeder, belt-drive seeder, vacuum seeder, andwalk-behind plate-type seeder. If youare an organic grower, check to makesure that the coating on pelleted seedis organic, because some pelletedseeds have pesticides in the coating.
✤ Plant seeds ¼-¾ inches deep,
✤ 8-12 seeds per row foot.
✤ Thin onions to 3-4 inches betweenplants and leeks to 4-6 inches.
In good conditions, seeds sprout 6-12days after planting. The besttemperature for allium seed sproutingis between 70-85°F.
You can also seed onions in the fieldto raise transplants for planting later.
To raise transplants in the field, plantseeds closer together; at about 30seeds per row foot. When plants are¼ inch in diameter dig them up andtransplant them.
Transplanting
Transplant onions in mid-April, afterfrost is out of the ground and about 4weeks before the last date that frostusually occurs. You can usetransplants that you grow yourself oryou can buy transplants. If you buythem, soak the roots right away in ashallow pan of water and plant themwithin a day or two. If you grow yourown transplants they will be ready togo out into the field when they are ¼inch in diameter.
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Alton N. Sparks, Jr., University of Georgia, 1328054 Bugwood.org
At transplanting, clip off tops to 5inches so the plants do not dry out asmuch while the root system grows.Plant transplants 1 inch deep and 4inches apart. Water transplantsimmediately.
Onion growth
Each onion variety needs a certainday length to start forming a bulb.Until the plant gets the critical amountof day length, it will grow new leavesbut not form a bulb. You can harvestand sell onions before they form abulb. These are called “greenbunching onions”.
After an onion starts to form a bulb,many factors affect its growth rate andsize. These factors are temperature,fertilizer, soil moisture, and havingenough space and light.
When a plant forms an early flowerand seed stalk it is called “bolting”.
Onions and other alliums bolt whenthe temperature is between 40-50°Ffor 1-2 months. Onions grown fromsets bolt if the temperature in springstays cool for a long time.
Garlic growth
Plant garlic from cloves. At harvest,you can save cloves to plant for nextyear. Big cloves grow into big bulbs.The flower stem of a garlic plant iscalled a scape. Tiny bulbs calledbulbils form at the top of the scape.These bulbils will grow into garlicbulbs but they will be too small to sell.
The best time to plant garlic bulbs isin the fall, 6-8 weeks before theground freezes. This gives garliccloves enough time to grow strongroots before winter. Do not plantgarlic in the spring. Warm springtemperature and longer day length inspring will cause garlic cloves to forma bulb too early.
In fall, plant cloves 4 inches apart inthe bed. 100 lbs of garlic will plant1000 ft2. Divide the bulbs into clovesjust before planting. If you divide thebulbs earlier, disease can infect thecloves more easily. Plant cloves withtheir points up. Plant garlic cloves 2-3inches deep and 4-6 inches apart.
Farmers usually plant garlic in doubleor triple rows in beds that are 2-3 feetapart. If you plant garlic cloves tooshallow, shoots will start to grow inthe fall. These tender shoots will bekilled in the winter and roots will notgrow as strong.
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Gerald Holmes, Valent USA Corporation,1571140 Bugwood.org
After the soil freezes, put a mulch ofstraw 4-6 inches thick over the plants.This will keep the soil frozen duringthe winter and prevent the soil fromheaving up and cracking. Heaving soiltears and dries roots.
In early spring, rake off the strawmulch to help warm up the soil andspeed growth. Some farmers leavethe straw mulch in place to addorganic matter to the soil.
Garlic needs nitrogen for best growth.If your soil has more than 20%organic matter, add 35 lbs nitrogenper acre during the growing season.On sandy soils with less than 2%organic matter, add 60 lbs nitrogenper acre during the growing season.
Divide the total amount of nitrogenyou need and add a little at a time sothe plant can take it up. If you plan toadd nitrogen twice, add half atplanting time and add the other half inspring about 2 weeks after you seesprouts grow. If you plan to add
nitrogen three times, add one third atplanting, one third in spring 2 weeksafter sprouts grow, and one third amonth later.
Garlic needs time to slow its growthand die back before harvest. Do notadd nitrogen in the last 60 daysbefore harvest.
In early summer when the scape onhardneck garlic has formed a circle,remove it and its bulbils. This will helpthe bulb grow larger with 8-10 cloves.You can sell the fresh garlic scapes(with or without bulbils) at market.They have a mild garlic flavor.
You can also sell green garlic, whichis garlic that is harvested before itforms bulbs. You can harvest greengarlic from small cloves, denseplantings, or plants that you havethinned from the field. Green garlichas a milder flavor than bulb garlic. Itcan be eaten raw or cooked.
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Elephant garlic growth
Elephant garlic is a little less hardythan regular garlic. Plant elephantgarlic the same way as regular garlicexcept for these differences:
✤ Plant elephant garlic cloves 2-3inches deep and 6-8 inches apart.
✤ In spring, break off any flowerbuds.
✤ Give elephant garlic about threetimes more nitrogen than regulargarlic.
Leek growth
Leeks tolerate colder temperaturesthan onions and garlic. Leeks growbest between 68°F and 78°F. Theygrow in soils similar to onions andgarlic, but they like wetter conditions.
Farmers usually start leek seedsindoors and then transplant them intothe field. Leek seeds take a long timeto sprout. Plant leek seeds in flats ¼inch apart and ¼ inch deep. Plantseeds in February and March. Whenthe plants are big enough to handle,transplant them into another flat andput them 1 inch apart. Then in mid tolate April, plant the leeks into the field.
Plant leeks 4-6 inches apart in therow and 18 inches apart between therows. When you plant leeks into thefield, dig a furrow or holes 5-6 inchesdeep. Leave at least 1-2 inches ofleaves above the soil surface. Leavethe soil loose around the base of thestem.
Leeks are sold “blanched”, or withwhite stems. The longer the whitestem, the higher the quality of leek. Toget leeks with white stems you mustcover the base of the plant with soilas it grows. Wait until the leeks putout new strong growth. Then startgradually filling in the furrow with soilhigher up the stem. Do not bury theplace where the leaf grows from thestem. You can use a cultivator or hoeto hill soil up the stem. Do this two orthree times during the growingseason as the leeks grow. At the endof the season, 5-6 inches of the stemwill be white.
Leeks grow slowly. It can take 120-150 days for leeks to mature.
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Leeks
Wild leek or ramp growth
You can collect wild leek or rampsfrom the wild if you follow these rules:
✤ Ask the landowner for permissionto collect the plants.
✤ Do not collect plants on publicland; it is prohibited.
✤ In each patch you find, collect onlya small amount and leave the rest.
✤ Collect no more than 5-10% andleave the rest. That means if yousee a patch with 20 plants, harvestno more than 2 plants.
✤ The rest of the plants will grow andkeep the population healthy.
You can grow your own wild leek orramps. Choose a shady, moistlocation that is well drained. The soilshould have a lot of organic matter.The shade could be from trees orfrom a shade structure that you buildin the field.
Wild leek or ramps are perennialplants that grow new leaves everyspring, from March-April. In June, theleaves die and the plant grows aflower stalk. The flower blooms inearly summer. Seeds form in latesummer. Seeds will stay dormant untilthey get a warm moist period andthen a cold period. After that they willbreak dormancy and sprout.
You can grow wild leek or ramps fromseed. ✤ Plant wild leek or ramps seeds in
the fall. If the seeds did not get awarm moist period and then a coldperiod, then it can take 18 monthsfor them to sprout.
✤ Plant enough seed so that youhave 5-7 times more wild leek orramps than you need to harvest.
✤ After planting, cover seeds with 2-3 inches of leaf mulch.
✤ Each year, harvest only 1/7 -1/5 ofthe plot. The rest of the plants willgrow and keep the populationhealthy.
✤ If you grow wild leek or ramps fromseed it will take 5-7 years until theplot is mature.
You can also grow wild leek or rampsfrom transplants or bulbs.
For transplants:✤ Plant transplants in March-April.
✤ Plant transplants to the samedepth they were growing.
✤ Cover with 2-3 inches of leafmulch.
For bulbs:✤ Plant bulbs in March.
✤ Plant bulbs 4-6 inches apart and 3inches deep.
✤ Leave the tip of the bulb above thesoil surface.
✤ Cover with 2-3 inches of leafmulch.
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Soils and Nutrient
Management
Get a soil test before you plant a fieldfor the first time and then at leastonce every 3 years. For informationon how to collect samples and whereto send them for analysis, seeUniversity of Wisconsin Extensionpublication Sampling Soils for Testing(A2100).
Most soil tests include pH, organicmatter, phosphorus, and potassium.You can also ask to test for nitrate-nitrogen, calcium, magnesium, sulfur,boron, manganese, and zinc. You willreceive the results of your soil testalong with fertilizer recommendationsbased on how you will use your field.You can also test your potting soil thatyou use to grow transplants.
Compared to other vegetables,onions and other alliums need a lot offertilizer and have shallow roots.
When you add fertilizer to thesecrops, put it in a strip alongside theplants, do not cover the planting bed.This is because the roots don’t grow
far away from the plant. Give onionsand other alliums nitrogen in 2-3small amounts during the growingseason instead of one large amountat one time.
Soil pH
Soil pH measures acidity and shouldbe at the correct level so the crop cantake up enough nutrients andminerals from the soil. Plants thatdon’t have enough nutrients andminerals can turn yellow. Onions andother alliums that don’t have enoughminerals can have leaves that growpoorly, grow twisted, and have otherproblems.
✤ For onions grown on most types ofsoil, the pH should be 6.5-8.0.
✤ For onions grown on peat soil, thepH should be 5.8.
✤ For garlic, the soil pH should be6.0-7.0.
✤ For leeks, the soil pH should be6.0-8.0.
✤ If the pH is below 6.0, apply aglimeto raise the pH.
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Howard F. Schwartz, Colorado State University, 5358545 Bugwood.org
Fertilizer needs
Onions and other alliums neednitrogen, phosphorus, and potassiumin large amounts and many othernutrients in small amounts.Compared to other vegetables,onions and other alliums need morephosphorus and potassium. They alsoneed more copper, manganese, zinc,and molybdenum. Check your soil testresults to see how much of thesenutrients you need to add. Onionsand other alliums have a shallow rootsystem, so they need small amountsof fertilizer often. Table C gives theamount of fertilizer these plants need.
Choose fertilizer from organic orinorganic sources. Healthy soil hastiny organisms (microbes) that breakdown organic matter into nutrientsthat plants need to grow. Over time,organic fertilizer can build your soiland make the soil more healthy andfluffy which lets plants grow more
easily. Inorganic fertilizers give plantsnutrients quickly but do not build thesoil. Some inorganic fertilizers have alot of salt which is bad for soilorganisms.
Organic fertilizers can come frommanure, compost, fish meal, bonemeal, and live compost tea thatincludes oxygen. Recent studies showthat live compost tea helps preventplant diseases and also givesnutrients to plants.
Live compost tea is made by carefullymixing fungi, bacteria, sugars, water,and a steady stream of air to growactive soil micro organisms.
If onions and other alliums do not getenough manganese, the plants growslowly and leaves turn light green andcurl. The neck of the plant becomesthicker but the plant is slow to form abulb. Some plants that do not getenough manganese gradually
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Table C. - Soils and nutrients
Annual nitrogen, phosphate, and potash for onion
Nitrogen Phosphate and potash
Organicmatter
Amount to applya Amount to applya
Yield Phosphate (P2O5) Potash (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 4.782.0-9.9 140 5.25
10.0-20.0 130 4.78
>20.0 120 4.5
become olive green and look wilted.Muck type of soils with a high pH arethe type of soils that would mostcommonly have too little manganese.
If onions and other alliums do not getenough zinc the plants grow slowlyand leaves start to twist and bend likea corkscrew. Younger leaves start toturn yellow between the leaf veinsand yellow stripes form up and downthe leaves.
Irrigation
Onions need water regularly becausethey have a small shallow rootsystem. Keep the top 3-4 inches ofsoil moist. Roots grow from a flat“stem plate” on the bottom of the bulb.Until the onion forms bulbs, this stemplate should not dry out. On sandysoil you might need to water everyday.
After the plants start to form a bulb,give them an inch of water a week.Soak the ground once a week so theplants form a strong root system. It isbetter to water heavily once a weekthan to water lightly several times aweek. Stop watering plants 1-2 weeksbefore harvest.
Garlic needs even soil moisture whenit is forming a bulb (April-June). Stopwatering plants 3-4 weeks beforeharvest (mid July-mid August) so thebulbs do not rot.
Leeks need less water than onions.After they begin to grow, they will onlyneed to be watered if there is a longdrought.
As plants grow, notice if leaves wilt inthe middle of the day. If so, they needwater. If plants wilt a few times, theywill produce a smaller yield. Plantsthat wilt often or for a long time mightdie.
Use either drip irrigation or sprinkler.Drip irrigation saves water and helpsprevent leaf diseases. Mulch can helpkeep moisture in the soil.
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Leaves
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Harvest, Handling, and
Storage
Onions
Harvest fresh onions when 15-25% ofthe tops have fallen over. Harveststorage onions when 50-80% of thetops have fallen over. If you harveststorage onions earlier, they might rotduring storage. If you harvest onionslater (after more than 80% of the topshave fallen over) they might getdiseases more easily in the field.
Harvest onions by cutting under theroots and lifting the bulbs. You can dothis with a tractor and a digger similarto a potato digger or you can do thisby hand with a spade or spading fork.
For green onions, harvest them whenthe tops are at least 6 inches tall and½-1 inches in diameter. Two to threeweeks before harvest, cover the baseof the stems with about 2 inches ofsoil to “blanch” them and keep themwhite.
At harvest, pull off the brown outerskin and trim the leaves. Makebunches according to the sizecommonly sold at your market. Mostbunches have 5-7 onions. Use arubber band to hold the bunchtogether. If you wear many rubberbands around your wrist you canmake bunches quickly. After harvest,keep green onions cool.
Storage onions need to be cured anddried. Afterwards, they will godormant and last longer. Storage
onions that have been cured are lesslikely to become infected withdiseases. Low humidity andtemperatures of 85-90°F are best forcuring. Leave the dry outer scales onthe bulbs while you cure the onions.
There are many ways to cure and dryonions. If you cure onions outside,protect them from moisture and directsun. Put onions in the shade in aplace that will not get rain or heavydew. Dry days with a good breeze willhelp cure and dry the onions. You canput onions on screens to help drythem.
Onions with dry outer scales and adry neck have been cured correctly.They can be stored for up to 6 monthsat 32°F and humidity levels of 60-70%. If the temperature in storage ishigher than 40°F, the onions mightsprout.
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Garlic
Harvest garlic when 2⁄3 of the tops aredry and the leaves collapse. Pull a fewbulbs when you think the plants mightbe ready to harvest and look at themto help you decide when to harvestthe crop. If you harvest too early thegarlic bulbs will be small. If youharvest too late, the skin might splitand lower the quality. If you leavegarlic bulbs in the field too long, thebulbs can rot and cloves can start tosplit off the bulbs.
Harvest garlic on a warm, dry day sosoil falls off the bulbs. The garlic willbe easier to clean. Harvest garlic bycutting under the roots and lifting thebulbs. You can do this with a tractorand a digger similar to a potato diggeror you can do this by hand with aspade or spading fork. Never pullgarlic bulbs without first loosening thesoil. Clean some of the soil off thebulbs.
If you plan to make and sell garlicbraids, leave the tops on. Braid themas soon as you can after harvest.Then cure and dry the garlic braidsthe same way you cure and dry garlicbulbs. There are many ways to cureand dry garlic.
✤ You can harvest the garlic bulbsand leave them in long rows to dryin the field for a few days. Afterthat, put garlic bulbs in plasticcrates with good air flow and leavethe crates in the field.
✤ You can put garlic bulbs in theshade in a place that has good airflow and where the bulbs will notget rain or heavy dew.
Cure and dry garlic for 30 days afterharvest. The bulbs will lose up to halftheir weight. Flavor will improve.
After curing and drying, prepare garlicfor storage.
✤ Peel off the outer one or two layersof skin.
✤ Trim roots to 1 inch.
✤ You can store garlic as is or withthe dry tops removed, trimmed, orbraided.
✤ If you trim the tops, leave them 1½ -2 inches long.
Store garlic at 32°F and in 60-70%humidity. It will keep up to 6 months. Ifthe storage temperature is higherthan 40°F, garlic cloves will sprout. Ifhumidity is higher than 70%, roots willstart to grow and mold might grow.
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Elephant garlic
Elephant garlic bulbs are ready toharvest when all the leaves start toyellow and the top is not yet dried.Elephant garlic bulbs are fragile. Theybruise easily. The thin papery outerlayer separates easily. When youharvest elephant garlic, carefullybrush soil away from the bulbs. Do notknock the bulbs together. Afterharvest, trim the leaves and cut offroots. Dry and cure the bulbs forabout 6 weeks. Often, elephant garlicis sold by the bagful in small net bags.
Leeks
Harvest leeks when they are stillgrowing. They should be 1 ¼-3 inchesthick, depending on the variety. Youcan keep leeks growing later in thefall if you mulch them with a thicklayer of mulch such as straw. This willkeep the ground from freezing. Toharvest, dig under the leeks and cutthe roots. Then pull out the plants.After harvest, trim roots and greenleaves. Wash leeks lightly or wipethem clean. You can harvest and sellthe immature greens and stems ofleeks all during the growing season.Store leeks at 32°F and 95% humidity.Leeks will keep for 2 months.
Wild leek or ramps
Harvest ramps when the leaves are12-18 inches tall. Be careful not todamage the bulbs. Keep them cooland moist when digging. Afterharvest, trim the roots and wash thebulbs. Pack them in waxed cardboardboxes and store them in a cooler.
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Preventing Stress on
Your Body
Try to prevent stress on your bodywhen you grow leafy greens.
✤ Try to prevent stooping or bending.
✤ Change your position often.
✤ Sit on a stool or a pail. You can usea stool that you wear as a belt, ora stool on wheels that rolls alongthe row like a cart.
✤ Use garden carts and wagons asoften as you can so you do not liftand carry so much.
✤ If you use a standard plasticcontainer that stacks and is easyto load, unload, and clean, you willsave time.
In the place where you pack yourcrops, try to have a smooth level floorso it is easier to work with carts andwagons.
✤ Set up your wash and pack areaso you walk, carry, stoop, andbend as little as possible.
✤ Set up work areas the same heightas a table.
✤ Short people might want to standon a stool to reach the tables morecomfortably.
✤ To move boxes of produce, thereare systems you can use withsmall pallets and hand pallettrucks.
✤ You can also buy roller table tomove heavy boxes of produce.
There are examples of tools thatmake work easier from the Universityof Wisconsin-Madison Department ofBiological Systems Engineering. Goto the department website(http://bse.wisc.edu/) and look under‘Department Links’ for the HealthyFarmers, Healthy Profits Project. Clickon Tip Sheets and go to the category
for vegetable growers.
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Weed Management
You must control weeds to grow agood crop of onions, garlic, or leeks.Weeds take water, nutrients, space,and light away from your crop. Also,weeds left in the field might havediseases or insects that can harmyour crop. Since the leaves on onions,garlic, and leeks do not grow to shadethe ground, weeds are more of aproblem on these crops. Be sure towatch your field for weeds andremove them as soon as you can.
Perennial weeds come up every year.Annual weeds start by seed and liveone year. Biannual weeds grow fromseed one year and flower the nextyear. Biannual weeds live only twoyears.
Before you plant, remove weeds. Youcan use these methods:✤ Pull weeds by hand.
✤ Smother weeds with a cover crop(such as buckwheat).
✤ Cover the soil with black plastic toheat it and keep out light.
✤ Use weed killer sprays (herbicidesprays).
During the growing season, removeperennial and annual weeds.✤ Cultivate or hoe regularly to
remove annual weeds.
✤ If you cultivate early in the seasonyou prevent most weed problems.
✤ If you use weed killers(herbicides), check and follow therules on the label.
✤ Certified organic growers can onlyuse approved organic weed killers.
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Howard F. Schwartz, Colorado State University, 5362043 Bugwood.org
Mulch helps keep weeds down and alsohelps prevent diseases and keeps thesoil moist. You can use black plasticmulch to prevent weeds. Black plasticalso helps warm the soil in the spring.
You can also use straw as a mulch. Athick layer of straw blocks sunlight fromreaching the soil. Weed seeds won’tsprout.
If you use chemical weed killers, besure you check the label andunderstand that the one you choose islegal for the crops you sell. Chemicalslegal for a home garden might not belegal if you sell the crops.
If you use chemical weed killers, besure the one you choose is meant forthe weeds found on your soil type. Theweeds that typically grow on muck soilsare different than the weeds thattypically grow on other soils.
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Pest and Disease
Management
Onion diseases
The common diseases that attackonions, garlic, and leeks are botrytis,downy mildew, onion smut, purpleblotch, and soft rot. All of thesediseases except soft rot are causedby different fungi. Soft rot is causedby a bacteria.
Use these techniques to preventfungus diseases in onions, garlic, andleeks:
✤ Plant resistant varieties.
✤ Plant disease-free seed.
✤ Do not plant in poorly drained soil.
✤ Wait 2-4 years before you plantonions, garlic, or leeks in the samefield.
✤ Keep the field clean of weeds.
✤ Destroy old plants, stems andleaves.
✤ Remove old onions, garlic, or leeksfrom the fields.
✤ Use drip irrigation instead ofsprinkler.
✤ Give plants enough fertilizer andwater.
✤ Harvest when the bulbs are mature.
✤ Prevent cuts and wounds on thebulbs.
✤ Dry bulbs well.
✤ Store bulbs at the righttemperature and humidity.
✤ Wash equipment after you use it.
Botrytis leaf blight
Description: A fungus invades theleaves. You see tiny oval whitish oryellowish spots on the leaves. If youcut the leaves you will see the spotsthrough the thickness of the leaf.
Disease cycle: Over winter, thefungus lives in soil or on parts ofonion plants left in the field. Sporesblow in the wind on to leaves or aresplashed onto leaves with rain orirrigation. If the plant has a cut orwound the spores enter the plant.
Management: Use the preventiontechniques listed above.
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Botrytis leaf blight
Botrytis neck rot
Description: A fungus invades theneck but you don’t see it until after thebulbs are harvested and stored. Softareas start to form around the neckand toward the base of the bulb. Thesoft areas look sunken, brown, andwater soaked.
Disease cycle: Over winter, thefungus lives in soil or on parts ofonion plants left in the field. Sporesblow in the wind on to leaves or aresplashed on to leaves with rain orirrigation. If the plant has a cut orwound the spores enter the plant.
Management: Use the preventiontechniques listed above and be surethe bulbs are dry before storage. Cuttops no longer than ½ inch at harvest.
Downy mildew
Description: A fungus invades andkills the leaves. The plant formssmaller bulbs that do not mature.Leaves on plants with downy mildewhave areas that are soft, pale green,oval, and look sunken. The tip of theleaf can flop over. With more time,infection makes the leaves turn palegreen and then yellow. If the weatheris moist, a fuzzy violet growth coversthe leaves. Downy mildew can alsostart on the older outer leaves and
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Downy mildew
Howard F. Schwartz, Colorado State University,5364053 Bugwood.org
Botrytis neck rot
move through the plant to theyounger, inside leaves. Downy mildewis worse in cool weather. Plants withdowny mildew get other diseasesmore easily.
Disease cycle: Over winter, thefungus lives in parts of diseasedplants left in the field. Downy mildewaffects onions, garlic, leeks, and otheralliums. Spores blow in the wind on toleaves of other plants. Wet weatherwith dew, fog, or rain causes moreinfection.
Management: Use the preventiontechniques listed above and also:
✤ Plant seed that is disease - free.
✤ Plant in soil that drains well.
✤ Plant to give good air flow betweenplants; don’t plant too closetogether.
Onion smut
Description: A fungus invades youngseedlings and kills them. At first, theleaves on seedlings get a blister thatis brown-black. Most seedlings die 3-5weeks after they sprout and getinfected. Some plants die slowly.Seedlings that live do not form bulbs.If bulbs form, they become covered inblack spots. Plants with onion smutget other diseases more easily.
Disease cycle: The fungus lives insoil for many years. When onions,leeks, or shallots are planted into theinfected soil, the spores sprout andinfect new seedlings. Over winter, thefungus lives in parts of diseasedplants left in the field. Spores blow inthe wind on to leaves of other plants.Wet weather with dew, fog, or raincauses more infection.
Management: Use the preventiontechniques listed above and plantseed that is disease-free.
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Howard F. Schwartz, Colorado State University,5361506 Bugwood.org
Onion smut
Purple blotch
Description: A fungus invadesonions, garlic, and leeks and causesplants to die early. At first, you seesmall, brown, water soaked areas ononion leaves, flower stalks, andflowers. As the spots get bigger theyhave light and dark purple areas thatlook sunken. The edge of the spot isreddish or purple with a yellow halo.With more time, infection makes theleaves and stems turn yellow, dropover, and die. This can take manyweeks.
At harvest or in storage, onion bulbscan be infected. The fungus gets intothe bulb through the neck or through
cuts in the bulb scales. If a bulb isinfected that part of the bulb slowlydries out. The area that was infectedbecomes papery.
Disease cycle: Over winter, thefungus lives in parts of diseasedplants left in the field. In warm wetspring weather the fungus makesspores. Spores infect leaves, stems,and flowers. Spores need rain ormoisture to infect plants.
Management: Use the preventiontechniques listed above and also:
✤ Plant seed that is disease - free.
✤ Plant in soil that drains well.
✤ Plant to give good air flow betweenplants; don’t plant too closetogether.
Soft rot
Description: A bacteria invadesonions, garlic, and leeks and causesthem to rot in storage. At first, yousee water-soaked areas near theneck of the bulb. It moves down alongone or more scale. Later, the areasare soft and slimy. The fluid stinks.
Disease cycle: The bacteria affectsmany different vegetables and plants.Bacteria is carried to onions, garlic,and leeks on rain, tools, clothing,insects, and running water. Bacteriainfects plants that are already weakfrom another cause. Bacteria alsoenters a plant through a cut or wound.Onion maggots can carry the bacteriaand adult flies can lay infected eggson onions.
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Howard F. Schwartz, Colorado State University,5362939 Bugwood.org
Purple blotch
Management:✤ Keep plants healthy.
✤ Prevent cuts and wounds on plants.
✤ Control onion maggots.
✤ Let tops mature before harvest.
✤ Let tops dry well.
✤ Handle onions carefully so theydon’t bruise.
✤ Destroy bulbs that have rot.
Insect Management
The common insects that attackonions, garlic, and leeks are asterleafhopper, black cutworm, onionmaggot, and onion thrips.
Aster leafhopper
Description: The aster leafhopper isan olive-green, wedge shaped insectabout 1⁄5 inches long. If you use amagnifying glass you will see 6 spotson the back of the adult’s head. Adultleafhoppers are very active and quick.They jump, crawl, or fly when they aredisturbed.
Immature leafhoppers are callednymphs. They have a similar shape tothe adults but they are cream coloredand do not have wings. Nymphs donot jump or fly but they crawl quickly.
Life cycle: Leafhoppers migrate inthe spring from states near the Gulf of
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David Cappaert, Michigan State University,2106081 Bugwood.orgS. K. Mohan, 5367341 Bugwood.org
Soft rotAster leafhopper
Mexico. Warm, southerly winds carrythe leafhoppers north. By June andearly July there are many leafhoppersin the Midwest. Adults begin to layeggs in leaves of certain plants,including many weeds and cropplants. Nymphs hatch 5-7 days later.They grow to be adults in 20-30 days.Usually there are 2-5 generations peryear.
Damage, symptoms: Both the adultsand the nymphs pierce the leaves andsuck sap out of the plant. The maindamage aster leafhoppers cause tocrops is infection with aster yellowsvirus. If a leafhopper feeds on a plantthat has the aster yellows virus, thenthe leafhopper carries the virus. Whenthat insect feeds on a plant, it cantransfer the aster yellows virus. Inalliums, the aster yellows virusdisease symptoms will appear aboutone month later. Plants infected withaster yellows virus turn yellow andweak. They produce smaller bulbs.Stems and leaves grow twisted. Bulbsinfected with aster yellows virus donot dry well.
Management: Remove weeds fromfield edges. Keep insects off plants byusing floating row covers, which arespecial sheets of white fabric made ofspun-bonded polypropylene. Thisfabric lets sunlight and water throughthe fabric but stops insects.
Row covers stop leafhoppers fromfeeding on onions, garlic, or leeks. Besure the fabric covers the crop fromthe beginning of the growing season
until 30 days before harvest. You canlay the fabric over the crop or use wirehoops to hold it up. Be sure to seal all4 sides of the fabric to the ground soinsects don’t fly under it. You can holdthe edges down by burying the fabricin the soil, or use weights to hold itdown such as metal posts or lumber.
If you decide to use chemical spraysto control aster leafhoppers you needto know how many leafhoppers youhave and whether they carry the virus.There are yellow sticky cards thatcollect insects so you can see them.Put these cards in the field attransplant time. Choose a spot justabove the crop and a few rows in fromthe edge.
When you see leafhoppers on thecards, begin to collect insect samplesevery week. Contact your local countyExtension office for information onwhat percent of the currentleafhopper population is infected.They can help you decide if you needto spray. If you spray, continue until 30days before harvest.
Some growers plant more than theyneed so that if some plants getinfected with aster yellows virus thenthere are still enough left to produce acrop. Growers also try to grow alliumsaway from other plants that can beinfected with aster yellows virus.Some of these plants are lettuce,celery, carrot, parsnip, parsley, dill,pepper, tomato, cucumber, and sweetcorn.
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Black cutworm
Description: Cutworms are larva of agrey moth that flies at night.Cutworms eat young leaves andstems. They can cut off manyseedlings in one evening. The large(1.5-2 inches) fat worm curls up into atight C shape when it is disturbed.They are grey with black dots alongthe sides.
Life cycle: Moths fly into the Midwestfrom southern states in late May. Theylay eggs on low growing plants orpieces of plants leftover from the year
before. They like to lay eggs on grassyplants. The eggs are either laid one byone or in a cluster. Eggs hatch intolarva which are also called cutworms.
The young cutworms feed at the tipsof the plants. Older cutworms feed atthe soil surface or just below. Oldercutworms feed at night or on cloudy
days. When they are not feeding theyburrow into the ground. Usually thereare 3-4 generations per year. The firstgeneration does the most damagebecause it eats seedlings.
Damage, symptoms: One largecutworm can destroy many plants inone evening. They often pull thestems into their burrow.
Management: Control grassy weeds.Do not plant in low, wet areas orplaces where grassy plants grew theyear before.
If you decide to use chemical spraysto control cutworms you need to knowhow many cutworms you have. Afteryou see feeding damage, look forcutworms every week. Walk betweentwo rows of plants and shake everyplant on either side along a 5-footlength of row. Count the larva that fall.If there are more than two cutwormsper foot of row they might causeenough damage for you to think abouta spray.
Onion maggot
Description: Onion maggots are thelarva of a fly that looks like a housefly.The flies are ¼ inches long. Theirwings overlap each other when the flyis resting. The larva or maggots looklike cream colored worms 1 inch long.The maggots do not have legs. Theirhead end is pointed.
Life cycle: Onion maggots overwinteras pupae in the soil or old onions.When the pupa forms an adult fly, itcomes out in mid-May. The fly lays
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Black cutworm
eggs on the soil surface at the base ofplants in the onion (allium) family.When the larva or maggot comes outof the egg it goes to the bulb andstarts feeding. Later in its growthcycle it forms a pupa in the soil. Threeto four weeks later another generationstarts.
Damage, symptoms: Onion maggotseat the plant at a spot just belowground. Sometimes they eat thewhole seedling. If the plant is olderand has started to form a bulb, themaggots can burrow into the bulb.After this the plants wilt and turnyellow. Plants that have been eatenby onion maggot can start to rot.
Management: If you see the damageit is already too late to control onionmaggots. The best way to controldamage from onion maggots is toprevent them from coming into your
field. Destroy old plants and bits of oldstems and leaves. Remove oldonions, garlic, or leeks from the fields.If you have onions, garlic, or leeksthat did not sell, do not pile them.Cultivating the field in the fall can helpkill pupae. If you have enough spaceor have fields that are far from eachother you can rotate crops. Newplantings have to be at least ¼ mileaway from fields that had onion cropsthe year before.
Onion thrips
Description: Thrips are tiny insectsyou will see more easily with amagnifying glass. They are 1/6 inchlong. Thrips have a long, shiny bodythat is pale yellow or brown andpointed at both ends. Their wingshave no veins. The edge of theirwings have long hairs. Immaturethrips (called nymphs) are smallerthan adults. Nymphs do not havewings.
Life cycle: Onion thrips overwinter asadults or nymphs on onion cropplants and pieces of plants leftoverfrom the year before. Thrips alsooverwinter on weeds in the field andnear the edge of the fields.
Females can reproduce withoutmating. They lay eggs beneath theleaf’s surface. Eggs hatch in 5-10days. Nymphs grow into adults in 15-30 days. One or two weeks after theyhatch, nymphs move into the soil andstop feeding. There are 4-8generations of thrips a year. There aremore thrips in hot, dry weather.
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Onion maggot damageDR. MICHAEL HAVEY, HAVEYLAB.HORT.WISC.EDU
Damage, symptoms: Thrips usetheir mouthparts to rasp their jaws likea saw blade. Then they suck the plantsap. Tiny white spots form on leaves.Spots can form into blotches andsilvery streaks that shine in the sun.Later, these areas become dry andyellow. If there are many thripsfeeding, leaf tips can turn brown.Bulbs of onions, garlic, and leekseaten by thrips are smaller and notshaped well.
Management: Thrips are hard tocontrol because they are small andhide between leaves. The leavesprotect them. Thrips also reproducequickly. Keep your fields and theedges of neighboring areas as weed -free as you can to prevent thrips. Youcan add helpful insects (beneficialinsects) such as lady bugs to eatthrips. There are some natural spraysthat you can use against thrips.Examples are soap spray, sulfer,neem, and a beneficial fungus calledBeauvaria bassiana. If you are an
organic grower, check to be surethese sprays fit the rules for organiccertification.
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This publication was developed by the University of Wisconsin-ExtensionEnvironmental Resources Center in collaboration with the WisconsinDepartment of Agriculture, Trade & Consumer Protection and supported by agrant from the USDA Risk Management Agency.
Text by Astrid Newenhouse, Associate Scientist, University of Wisconsin-Extension Environmental Resources Center. Special thanks to Karen Delahaut.
Layout and design by Laurie Lawrence, Agency Art Director, WisconsinDepartment of Agriculture, Trade & Consumer Protection.
The publication can also be viewed and printed from pdf format on the web athttp://learningstore.uwex.edu/
Copyright 2011 by the Board of Regents of the University of Wisconsin System.University of Wisconsin-Extension is an EEO/Affirmative Action employer andprovides equal opportunities in employment and programming, including Title IX and ADA requirements.
UWEX Publication A3904-03 (05/11)
WI DATCP pub#: mk_fc_82.qxp (05/11)
