garlic - hannan

7/30/2019 Garlic - Hannan

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Crop Profile for

Garlicin WashingtonProduction Facts

Washington State ranks fourth in the United States in both thenumber of farms growing garlic and in harvested acres (1).

Garlic acreage has increased substantially in Washington in recentyears. Most of this increase has taken place in the eastern portion ofthe state.

Approximately 90 farms in Washington grew garlic on a total of 414acres in 1997 (1). Seventy-nine of these farms were irrigated.

In addition to bulbs grown for the fresh market, garlic is also grownin Washington for seed and dehydration.

Typical fresh market garlic yields range from 6,000 to 18,000 lbs.per acre.

Production RegionsCommercial garlic is produced in many Washington counties, much of itby small-scale growers. The leading counties are Klickitat, Okanogan,Thurston, and Yakima. Other counties where garlic is grown includeGrant, King, Pierce, and Spokane.

Okanogan

Yakima

Klickitat

Spokane

Grant

King

Pierce

Thurston


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General Information

Garlic (Allium sativum L.) is an ancient cropthat originated in Central Asia. It has been grownfor culinary, medicinal, and religious purposes forseveral millennia. Garlic is grown for its ediblebulbs, which are composed of a number of cloves.The bulbs can be eaten fresh, cooked in variousways, processed into a dehydrated product, orsaved for seed to be planted later. Garlic leaves andflower stalks are also edible.

Garlic can be profitably produced in bothlarge or small-scale commercial production systemsin the temperate climate of the Pacific Northwest.Current garlic varieties respond to both the tem-peratures and photoperiod of the latitudes in

Washington. Some clones are already adapted tothese climates.

Types of GarlicThere are two general categories of garlic,

hardneck and softneck (see diagrams, page 3).Both are produced commercially, but most of thegarlic grown in Washington is softneck. Whileboth types begin growth with leaf production, thehardneck types produce flower stalks, called scapes,by mid- to late-spring. The scapes extend, grow,

and coil during early growth, then as the plantmatures the scapes straighten out. Numerous clas-sification schemes of the hardneck types have beenproposed in the scientific literature and/or popularpress based on clove configuration, clove size, andbulb wrapper skin coloration.

Hardneck garlics are represented by varietiesthat may be red, purple, purple-striped, or white.With some of these varieties, the scapes are often

topped with a cluster of small round propagulescalled bulbils, which are also referred to as topsets.In general, hardneck garlic bulbs contain fewer,but considerably larger, cloves than bulbs of thesoftneck types.

The softneck garlics are often referred to assilverskin or artichoke garlic, and are mostcommonly represented by the varieties CaliforniaEarly and California Late. Silverskin garlic mayalso be differentiated into many-cloved or few-cloved varieties. The bulbs are usually all white,

but can be purple-tinged. Numerous strains ofthese exist, having been selected over the years bythe various companies that produce them fordehydration or growers producing them for freshmarket.

It should be noted that a garlic relative, el-ephant garlic, is often grown for commercial pro-duction. Elephant garlic is a different species,Al-lium ampeloprasum, than garlic. It is not a truegarlic, but a type of leek that produces very largecloves, often only three or four per bulb. Severalsmall bulblets may also develop on the bulb. Itproduces a large scape and umbel (flower head)that may be cut and sold to florists. In the spring,the tender lower portion of the scape is also usedfor fresh vegetable dishes.

Garlic is relatively easy to grow and can be aprofitable crop for large- and small-scale growers.However, profitability in garlic requires good yieldsand high quality. Because of the cost of seed andGarlic stalks or scapes with topsets.

Cross-section of Korean Six Piece, a hardneck

garlic variety.


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labor, garlic is a relatively expensive crop to grow.Garlic weed control is largely manual, thereforelabor-intensive, and many small-scale growers usehand labor for planting and harvesting as well.

Planting stockMany garlic cultivars are grown

commercially in Washington State. Some large-scale growers grow California Early andCalifornia Late. While both are consideredsoftneck, California Late often produces scapesunder Washington State growing conditions.Small-scale growers often prefer hardneck types.Asian Tempest, Chets Italian Red, and Musicare among the cultivars planted by small-scalegrowers.

Garlic is responsive to temperature and

photoperiod for proper clove and bulb formation,and subsequent scape development of some vari-eties. Because of this, significant differences inyield can occur, even with plantings of the samevariety.

Growers emphasize selection of clean, dis-ease-free garlic lines adapted to the area of pro-duction. Bulbs and cloves used for planting cancarry and transmit diseases such as white rot,basal rot, and possibly gray mold. Penicillium is afungus that can cause a decay of seed cloves and

reduction of stand. Other important pests thatcan be carried on the seed cloves include severalspecies of nematodes, such as the stem and bulbnematode. Some of these diseases and pests maycontaminate the soil and make the fields unus-able for future garlic and onion production.

Garlic for seed purposes is stored at 50Fwith a relative humidity (RH) of 55 to 65%.Garlic cloves break dormancy and sprout mostrapidly at 40 to 50F; hence prolonged storage atthis temperature range is avoided. Storage ofplanting stock at temperatures below 40F mayresult in rough bulbs, side-shoot sprouting, andearly maturity. Storage above 65F may result indelayed sprouting, late maturity, or accelerateddesiccation of bulbs.


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Cultural Practices

Soil PreparationGarlic will grow in almost any well-drained,

friable soil. Friable soils with good organic contentallow the bulbs to expand without becoming mis-shapen and aid in the soils water-holding capacity,which is important due to the relatively restrictedrooting characteristic of garlic. Soils must have apH above 6.0. The ideal pH for garlic is between6.5 and 7.0.

Growers have the soil tested for nutrients foreach field planted in order to best determine thefertility needs. The amount of nitrogen and irriga-tion used will directly affect not only the yield, interms of bulb size, but also can affect disease sus-

ceptibility and post-harvest storability. A baselinerecommendation for production in Washington is150 lbs. nitrogen per acre (N/A) and 15 lbs. sulfurper acre (S/A), plus potassium and/or phosphate asneeded. Growers apply 50 lbs. N/A and 5 lbs. S/Aat planting in the fall. They make a second nitro-gen application in early spring when the garlicbegins to grow again, then a final application inearly to mid-June. Some growers successfully com-bine the last two fertilizer applications into one,but it is recommended to split the last 100 lb. N/A

into at least two applications. It has been reportedthat witches brooming can result from using toomuch manure or high levels of nitrogen during thewinter.

PlantingFor maximum yield of fresh market garlic,

growers plant in the fall, from mid-September to

mid-October. Both softneck and hardneck varietiesgenerally survive the harsh winters of easternWashington, when the planting is done at leastfour to six weeks before the ground freezes. Plant-ing can also be done in early spring, albeit withsome loss of yield potential. In western Washing-ton, garlic is planted in late fall (e.g., November)or very early spring (e.g., March) (2). Some culti-vars may produce a high percentage of unmarket-able rounds, bulbs composed of a single clove,when planted in the spring (3).

Optimally, the seed bulbs should becracked or broken into cloves no more than afew days before planting, although this can bedone up to ten days before planting without anyreal adverse affect. Cracking in Washington State isgenerally done by hand, however, in the case oflarge-scale operations, machines with rubber-facedrollers are used to speed up the process. Regardlessof the method used, it is important to avoiddoubles and not to damage the cloves when crack-ing the bulbs. Doubles produce misshapen bulbs.Injured cloves are more prone to infection by dis-ease organisms. Cloves, regardless of size, will pro-duce garlic plants, but there is a definite correla-tion between the size of the clove and, underproper growing conditions, the size of the bulbharvested. It is common for growers to select thelargest, most healthy cloves from large, healthybulbs for planting.

Eastern Washington garlic field.

Healthy Washington State garlic begins with

soil preparation and proper planting.


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It has been shownthat there is a definiteeffect of clove orienta-tion at planting on thetotal yield and quality ofbulbs harvested. Clovesshould be planted verti-cally, with the basal root plate down. This is opti-

mum, but if cloves are planted with a mechanicalplanter, like a cone drill, and do end up lying hori-zontal, the emerging plants will often right them-selves in the early growth stages. Studies conductedwith three cultivars in the Columbia Basin showedthat planting garlic cloves upright or sideways re-sulted in the highest plant stand and the greatestyield (3). When planting by hand, growers find itis worthwhile to take care to plant cloves upright.Cloves planted upside-down were found to beslower to emerge and produced bulbs that were

smaller and tended to be deformed.Cloves are planted two to three inches deep

on a 2- to 4-inch spacing in the row. The size ofthe field, irrigation system, and cultivation equip-ment and practices dictate the row configuration.

Garlic planted in double rows on raised beds.

Upright (left) and inverted

(right) garlic cloves. Planting

orientation can play a role.

Garlic can be successfullyplanted and grown ondouble plant-row raisedbeds, in single rows on theflat, or in a dense planting

matrix. In central Washington, raised beds, 36-40

inches from center to center, with two rows perbed are commonly used. The rows are spacedabout 12 inches apart.

IrrigationGarlic can be successfully grown using fur-

row, sprinkler, or drip irrigation. Because garlic hasa relatively shallow root system, it is sensitive tomoisture stress throughout the growing season. Astraw mulch can help retain soil moisture. Garlicgrowers typically plant into moist soil. For fall-

seeded garlic in eastern Washington, one wateringmay be necessary before winter if the soil becomesdry. Irrigation resumes in the spring. In westernWashington, irrigation may be required in May,June, and July (2). Irrigation is continued until thebulbs reach the desired size and have two to threematured scales surrounding the bulb. Garlicshould not be irrigated once the tops dry and be-gin to fall to the ground.

Scape RemovalAlthough most garlic growers do not remove

scapes, some data suggests a positive yield responseto scape removal with hardneck types. In trialsconducted by WSU Cooperative Extension in theColumbia Basin, scape removal, or topping as itis sometimes called, was useful in increasing bulbsize and hastening maturity (4). If removing thescapes is planned, the best results come from cut-ting the scapes just above the top leaf whorl when


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they reach the full-coilstage. If growers wait untilthe scapes have fully elon-gated and are straight, theincrease in yield is negli-gible. If an early harvest isdesired, the removal ofscapes will hasten the senes-cence or death of the leaves.Additionally, tender scapescan be used as a high-value,seasonal fresh market pro-duce product.

HarvestDepending on the

type of garlic being pro-

duced and growing condi-tions, yields can range up to18,000 lbs. per acre. Typical harvest dates in cen-tral Washington range from early July throughmid-September, although harvest can occurslightly earlier or much later. Garlic is harvestedwhen the lower leaves are half to three-quartersbrown, and there are still some partially green up-per leaves. If a grower waits until all of the leavesare brown, the wrapper leaves of the bulb will dete-riorate, leaving a naked bulb. This is especially true

of the hardneck types, where the cloves will alsopull away from the scape, thusresulting in an unmarketableproduct. In general, spring-planted garlic must be harvestedlater in the year than fallplanted crops.

Garlic is lifted from thesoil without bruising or cuttingthe bulbs. In medium to small-scale production operations,gathering the plantsfrom the field is doneby hand. During thisprocess, workers donot bang the soil offthe roots, but give thebulb a quick hand rubor a shake to get the

soil off, leaving an uninjured bulband one to two inches of roots.Although some growers wash thebulbs soon after digging the crop,this not necessary. Bulbs cannot beleft in the field under the sun todry out as they will get sun scald ormay exhibit greening from excessivesunlight. The crop is removed fromthe field and cured in a shady, well-ventilated location. Plants can bebundled and hung, put loosely innet bags and hung, or laid out onscreen shelving to dry.

Most growers wait until thecrop has cured and dried ad-equately before cutting the tops

and roots, generally by hand. Aboutone inch of stem and a half inch or

so of roots are left on the bulb, which helps pre-vent infestation by a number of storage diseases.

Garlic grown on a large scale or for dehydra-tion is typically harvested by machine. The driedtops may be burned off using propane flaming.Flailing is also used to remove the tops after whichthe bulbs are lifted using equipment such as potatodiggers. As with hand-harvested garlic, the bulbsare generally allowed to cure in the field for one to

two days. The bulbs are then harvested into trucks

Removing garlic scapes.

Garlic grown on a large scale or for dehydration

is typically harvested by machine.


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and loaded into bins for storage and shipping tointended markets.

StorageDepending upon the type, well-cured and

well-cleaned garlic bulbs can be kept in storage forup to 12 months. For long-term storage of clean,dry bulbs, most references recommend tempera-tures between 30-32F and low (60-70%) RH. If

freezing storage facilities are not available, it hasbeen shown that many cultivars of garlic will storeseven months or more at 55-58F and 55-60% RHin conditions with good air circulation. Whengarlic is chilled at temperatures between 35-50F,dormancy is broken and the cloves begin to sprout,especially under high RH conditions. High hu-midity conditions also promote the growth of stor-age pathogens and promote post-harvest diseases.

Weeds

Weeds are a major concern for farmers wher-ever garlic is grown. Garlic requires nearly perfect

weed control since it emerges slowly and neverforms a canopy with its short, vertical leaf arrange-ment (8). The long growing season required forgarlic production subjects garlic to competitionfrom successive flushes of weed growth. Whenplanted in the fall, garlic must compete with win-ter annuals in the fall and winter and with springand summer annuals in the following year.

Numerous weed species are troublesome ineastern and western Washington. Among the com-mon annual broadleaf weeds are lambsquarters

(Chenopodium album), Russian thistle (Salsolaiberica), kochia (Kochia scoparia), mustards (Bras-sicaspp.), shepherdspurse (Capsella bursa-pastoris),and pigweeds (Amaranthusspp.). The most impor-tant annual grass weeds are annual bluegrass (Poaannua) and barnyard grass (Echinochloa crus-galli).Canada thistle (Cirsium arvense), field bindweed(Convolvulus arvensis), and quackgrass (Agropyronrepens) are widespread perennial weeds. Volunteerpotato and cereal crops can be troublesome weeds

in fields where these crops are grown in rotationwith garlic.Weeds reduce yields of garlic by direct com-

petition for nutrients, water, and space. Largeweeds can reduce air movement in garlic fields,increasing the risk of diseases such as neck rot.Heavy weed growth also slows the drying down offoliage prior to harvest. In general, harvesting op-erations are more difficult in fields where weedshave not been properly controlled.

Cultural ControlCultivation is a key component of weed

control in all garlic fields in Washington State.Most garlic growers cultivate at least once duringthe growing season in addition to the cultivationthat takes place when the field is prepared forplanting. Mechanical cultivation is the preferredmethod on large fields. Typical cultivation equip-ment includes cultivators with knives or smalldisks. Finger weeders are also used where garlic isplanted in single rows. This piece of equipmentworks best when the ground is relatively soft and

Mature pigweed.


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the garlic has established an ad-equate root system. Shallow culti-vation is preferred, both to avoiddisturbing the root system of thegarlic plants and to prevent weedseeds that are buried deeply frombeing brought to the surface. Onsmall fields, growers often rely onhand weeding. Hand weeding isused sparingly on large fields,primarily to control large weedsthat have escaped other methodsof control.

Some small-scale growersuse mulch as a component of theirweed control program. In additionto suppressing weeds, mulch can

also serve to conserve soil mois-ture and provides some degree ofprotection from severe cold in thewinter.

Flaming is also used on a limited scale forweed control in garlic. In organic production,flaming is done pre-emergence to reduce the need

for hand weeding. Organic grow-ers prepare the field so that asmany weeds as possible emergebefore the crop. Successful weedcontrol in garlic requires an inte-grated approach utilizing a varietyof techniques.

Chemical ControlRelatively few herbicides

are registered for use on garlic. Ingeneral, growers recognize thatweeds are easier to control whensmall. Cool soil and air tempera-tures in the fall can reduce theefficacy of some herbicides. Acommon herbicide combination

is a broadleaf herbicide, such asbromoxynil, plus a grass herbi-cide, such as sethoxydim orfluazifop. Mechanical cultivation

and hand weeding are almost always used in con-junction with herbicides for control of weeds ingarlic.

Some small-scale growers use

mulch as a component of their

weed control program.

Chemical Target Weeds Application Rate Timing

glyphosate

(Roundup, others)

Annual grasses andbroadleaves andsome perennials

Rate depends on target weed Pre-emergence

pendimethalin(Prowl)

Annual grasses andbroadleaves

0.75 to 1.5 pounds ai per acre, ratedepends on soil texture, lower ratesare used on coarse textured soils

Pre-emergence orpost-emergence

bromoxynil(Buctril, others)

Broadleaf weeds0.25 to 0.38 pounds ai per acre,applied when weeds


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Diseases

WHITE ROTSclerotium cepivorum

White rot, caused bySclerotium cepivorum, isa key disease of garlic in Washington. Althoughnot currently present in all parts of the state, theseriousness of white rot makes it a concern for theentire industry. Once introduced into a field, thesclerotia may survive for 20 to 30 years withoutthe presence of an Allium host. Fungal activity isfavored by cool soils and is restricted above 75F.OnlyAllium spp. are attacked.

Leaves decay at the base, turn yellow, wilt,and topple over (5). Older leaves collapse first.Roots rot and the top of the plant can be pulledout of the ground easily. Roots and bulb may becovered with a fluffy white mycelium. Affectedbulbs may become watery, and the outer scalescrack as the bulb dries and shrinks. Small blacksclerotia form on and in affected bulb parts.

Cultural ControlGrowers plant onlydisease-free cloves and

plant in onlydisease-free soil. They use sanitationto avoid introducing white rot via contaminatedsoil carried in on equipment or shoes.

A white rot quarantine area exists inAdams, Franklin, and Grant counties prohibit-ing the importation of vegetative planting mate-rial of onion, garlic, leek, chives, shallots, andother Allium spp. except those produced in andshipped from a white-rot-free area and certifiedto be free of white rot.

Chemical ControlChemicals are not used by growers to con-

trol white rot. Under most conditions, even thebest chemicals control only a portion of the dis-ease, and soils become useless for the production ofgarlic and otherAllium spp. Exclusion is the bestway to control white rot. Once this disease is es-tablished in a field, it is very difficult to grow anyAllium spp. successfully.

BASALROTFusarium culmorum

Basal rot of garlic is caused byFusariumculmorum. Soilborne inoculum infects garlicthrough the stem plate rather than through rootsor storage leaves (5). Leaves of infected plants maynot produce disease symptoms, but can be a sourceof the disease. Transmission can occur when in-fested soil or debris is transported on equipment,seed, or runoff water. The fungus can survive in-definitely in the soil. Fusarium culmorum can also

infect elephant garlic, but not to the same degreeas garlic. Onion is not a host.

Symptoms include pre-emergence decay ofcloves and seedlings. Stem plates and storage leavesmay decay in the field during the growing season.Lesions may have a reddish fringe. Disease expres-sion is erratic from year to year and field to field.Post-harvest decay may involve a single clove orthe entire bulb.

Cultural Control

Growers commonly rotate garlic with non-host plants to reduce disease pressure. Cereals are ahost of garlic strains ofFusarium culmorum. Grow-ers also avoid planting in fields with a history ofbasal rot problems.

The primary cultural control of basal rot iscuring bulbs properly before storage and storingthe garlic at cool temperatures, as F. culmorum isfavored by warm conditions.

Chemical ControlGarlic growers in Washington seldom use

chemicals to control basal rot.

continued next page


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LEAF BLIGHTBotrytis squamosa

Several different Botrytisdiseases occur inWashington State garlic. Botrytis squamosacausesleaf blight on garlic. Onions are also susceptible.This disease is generally a problem only late in theseason under conditions of high humidity, exces-sive rain, or irrigation (5). The fungus can over-winter in cull piles or in the soil and spores arespread by the wind.

Leaf spots appear as small circular-to-ellipti-cal, grayish-to-white lesions with a green halo.Under conditions of high humidity, the spots mayenlarge, blighting the leaves.

Cultural ControlGrowers generally rotate garlic with non-

host crops, avoid excessive irrigation, and destroygarlic and onion cull piles.

Chemical ControlSeveral chemicals are registered for use on

garlic, but growers seldom use fungicides to con-trol leaf blight. Damage is generally not severeenough to warrant the use of chemical sprays.

NECKROTVarious species includingBotrytis porriandB. aclada

The fungus organisms that cause neck rot,includingBotrytis porriand B. aclada, survive thewinter as sclerotia on dead plant parts in the soiland on infected bulbs. Infection occurs throughneck tissue or through wounds. In garlic, neck rotis generally a more serious problem than is leafblight.

Symptoms may first appear on the neck ofthe plant near the soil line in the spring. The fun-gus moves rapidly into the neck region of the bulbscausing a water-soaked appearance. A gray mold

BLUE MOLD ROTPenicillium spp.

Several species ofPenicillium can cause bluemold rot in garlic. Infected bulbs are covered withcharacteristic blue-green spores and entire clovesmay be filled with spores (5). Infected cloves fail toemerge after planting. Blue mold rot can also in-fect elephant garlic and, occasionally, onions.

The fungus does not survive long in the soiland is generally transmitted on seed cloves. Infec-tion first occurs on wounds sustained when clovesare separated from the parent bulb. Blue mold isone of the most common storage diseases of garlic.

Cultural ControlBulbs are harvested carefully to avoidwounds and bruising, then promptly dried orcured. Growers plant cloves promptly after crack-ing to minimize blue mold infection.

Chemical ControlGrowers do not use chemical control for

blue mold rot as cultural controls are sufficient atpresent.

Blue mold rot in garlic is caused by various

Penicillum species.


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develops on the surface, later producing black scle-rotia. Before bulbing, plants may die or recoverdepending on weather conditions. Bulbs infectedlate in the season break down and are often in-fected by other disease organisms.

Cultural ControlGrowers avoid excessive nitrogen and irriga-

tion, especially late in the season. They practicegood weed control to aid air movement throughfield and to keep relative humidity low. Whenharvesting, growers allow tops to mature, then liftor undercut plants to avoid bruising and mechani-cal injury. Finally, they make sure that the garlic isproperly cured before storing.

Chemical Control

Fungicides are not generally used by growersagainst neck rot, as cultural methods control thedisease at this time.

STEM AND BULB NEMATODEDitylenchus dipsaci

A race of the stem and bulb nematode,

Ditylenchus dipsaci, has been recently found inWashington State. They are spread primarilythrough infected planting material. The nematodecan live in stored plant tissue for at least nine years,but they decline rapidly in soil (5). Hosts for thegarlic strain of stem and bulb nematode includegarlic, onion, leek, and chive.

Diseased cloves generally show no symp-toms, but the presence of nematodes can be de-

tected by examining tissue with a microscope. Inthe field, leaves become yellow and dry prema-turely. Plants can be stunted. The whole bulb mayseparate from the basal plate. High temperaturesbring on symptoms quickly.

Cultural ControlGrowers strive to plant only nematode-free

cloves. They rotate garlic with non-host crops anderadicate volunteer garlic plants from fields bycultivation or application of glyphosate (see Weedssection, above).

Planting seed that has been treated with hotwater (a treatment also useful for control of bulbmites) has proven effective for some growers.

Chemical Control

There is a Section 24c special local needslabel (WA-000018) for oxamyl (Vydate) for con-trol of stem and bulb nematodes on garlic inWashington State, valid through 12/31/05.

VIRUSES

Viruses, which can reduce yield and quality,

are a widespread problem on garlic grown inWashington State. Numerous viruses infect garlic,such as onion yellow dwarf virus and garlic mosaic,but few have been studied to any great extent, andthere are no assay methods currently available.Although virtually all planting material containsvirus, infections are usually mild. Virus-free plant-ing stock can be obtained only through tissue cul-ture. In the field, aphids and thrips are possiblevectors, transmitting virus from infected to healthyplants.

Symptoms include changes in color, mosaic,striping, streaking, and leaf distortion. Infectionsmay not produce visible symptoms or yield lossunless the plants are stressed. Plants may becomestunted and bulb size reduced, especially whenunder stress from soil moisture or low fertility.

Chemical Application Rate

oxamyl(Vydate L)

Preharvest

Interval

14 days

2 to 4 quarts per acreat planting as in-furrowspray or post-emergence at 2 to 4quarts in 20-40 gallonsof water per acre in a 1to 2-inch band


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Cultural ControlOnly large, healthy

cloves are planted. Plantsexhibiting severe virussymptoms in the field arerogued out. Good soil fertil-ity and proper soil moistureare maintained during thegrowing season to avoidplant stress.

Chemical ControlGrowers do not treat

with chemicals to controlviruses; they rely on culturalcontrols to keep the plantshealthy.

Insects and Related Pests

BULB MITESRhyzoglyphusspp. andTyrophogusspp.

Bulb mites are shiny, cream-colored crea-

tures with four pairs of short brown legs. Theyhave a wide host range that includes onions. Bulbmites can be introduced into a field on infestedcloves and can survive on decaying vegetation inthe field after harvest.

Damage results from bulb mites penetratingthe outer layer of bulb tissue allowing the entry ofdisease organisms. Bulb mites can reduce stands ofgarlic, stunt plant growth, and promote rot instored bulbs.

Cultural ControlGrowers plant only mite-free cloves. Hot

water treatment is occasionally employed to reducechances of infestation. They also allow the fields tolie fallow for natural breakdown and decomposi-tion of crop residue. Mite numbers can increase ongreen manure crops. Avoid planting successiveonion or garlic crops.

Garlic plants showing virus

symptoms (leaf striping).

Chemical ControlSoil fumigation with metam sodium

(Vapam, Sectagon) can reduce bulb mite numbers,however, soil fumigation is rarely used for garlic.Some growers plant garlic following a crop such aspotatoes or carrots that was fumigated.

THRIPSFrankliniella occidentalis

andThrips tabaci

Thrips are small, slender insects. Westernflower thrips, Frankliniella occidentalis, are typicallymore abundant in fields than onion thrips, Thripstabaci. Adults are pale yellow to light brown incolor, with feathery wings (7). It is very difficult todistinguish between these two pests without usinga dissecting microscope. Young thrips, callednymphs, are pale yellowish-green and wingless.Thrips thrive in hot, dry conditions and are moredamaging when such conditions persist for muchof the growing season. These insects have a widehost range, including cereals and broadleaf crops.Generally thrips are a more serious pest of onions


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than of garlic. Both adults and nymphs feed onfoliage. When foliage is severely damaged, it be-comes scarred and silvery in color. Yields can bereduced.

Cultural ControlGrowers avoid planting garlic near cereals, as

thrip populations build up in cereals in the springand migrate to nearby fields. Growers find thatoverhead irrigation provides a measure of suppres-sion.

Chemical ControlInsecticides, such as lambda-cyhalothrin

(Warrior T, applied at 0.02 to 0.03 lbs. ai/A) andzeta-cypermethrin (Mustang, applied at 0.0375 to0.05 lbs. ai/A), are used only when thrip popula-

tions are high and damage is evident. Resistance toorganophosphate and pyrethroid insecticides hasbeen noted in Western flower thrips.

WIREWORMSLimoniusspp.

Wireworm is a pest of many crops in Wash-ington, including garlic. The larvae, which can live

in the soil for two to six years, are jointed, lightbrown in color, and about one inch in length whenfully grown (7). They feed on bulbs and can de-stroy the crop. The adults, known as click beetles,do no direct damage.

Cultural ControlCrop rotation is an important practice in

controlling wireworms (7). Populations tend tobuild up in fields where grains or vegetable cropsare grown. Weedy conditions also favor wire-worms. When possible, growers select fields withno history of wireworm problems.

Chemical ControlSoil fumigation with dichloropropene

(Telone II) can reduce wireworm numbers, how-ever fumigation is seldom used for garlic. Somegrowers plant garlic following a crop that was fu-migated, such as potatoes or carrots.

Pest Control Issues

Garlic growers in Washington State integratea wide variety of cultural methods into their pestmanagement systems. Field selection, crop rota-tion, and the use of vigorous, pest-free plantingmaterial are critical components for a successfulgarlic crop. The chemical methods mentioned areimportant for situations where disease pressure isgreat. Generally speaking, large-scale growers relyon chemicals to a greater degree than do small-scale growers.

While many growers do not treat for diseasesor insect pests, herbicides are widely used in con-junction with mechanical cultivation and handweeding. The most common and successful herbi-

cide application combines a broadleaf herbicidewith a grass herbicide. With very few herbicidechoices registered for garlic, it is important thatgrowers have bromoxynil, fluazifop, glyphosate,pendimethalin, and sethoxydim available to them.

Diseases play a role in Washington garlicproduction as well. More pressure exists on thewest side of the state where conditions are wetterand in garlic grown for planting stock. These seg-ments of the industry need fungicides they can relyon. Planting stock garlic undergoes more intensive

disease management than garlic for the fresh orprocessing markets, as it is important to ensureclean seed (9). Oxamyl for stem and bulb nema-tode control is generally used only on garlic grownfor seed, and is therefore a critical component ofthis segment of the industry.

At present, white rot is not a widespreadproblem, but this disease can be devastating to theprospects of growing anyAllium spp. Resistantcultivars and/or a fungicide effective against whiterot would be a useful addition to future pest con-trol tools.


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Authors

Richard M. HannanUSDA/Western Regional Plant

Introduction StationWashington State UniversityPullman, WA 99164-6402Telephone 509-335-3683Email [email protected]

Erik J. SorensenWSU Cooperative Extension1016 N. 4th AvenuePasco, WA 99301Telephone 509-545-3511Email [email protected]

Acknowledgements

The authors are grateful to Todd Crosby(Mercer Ranch), Greg Anthony Lutovsky (IrishEyes with a Hint of Garlic), and Gary Q. Pelter(WSU Cooperative Extension) for their help inproviding information on garlic production andpest management and for reviewing thispublication. We also thank Jim Anderson of FilareeFarms for use of his hardneck and softneck garlicillustrations.

References

(1) USDA, National Agricultural Statistics Service, 1997 Census of Agriculture.

(2) Moore, J.F., L. Campbell, W.P. Mortensen, and A.J. Howitt, 1954, Growing Garlic in WesternWashington, State College of Washington.

(3) Sorensen, E.J., G.Q. Pelter, and R.W. VanDenburgh, 2000, Columbia Basin Garlic Study Re-sults, In: Proceedings of the Pacific Northwest Vegetable Association Annual Convention, Pasco,Washington, November 13-14, 2000.

(4) Pelter, G.Q., E.J. Sorensen, R.W. VanDenburgh, and R.W. Hannan, 2000, Effect of Scape Re-moval on Bulb Yield and Quality of Garlic Grown in Central Washington, In: Proceedings of the3rd International Symposium on Edible Alliaceae, Athens, Georgia, October 29-November 3,2000.

(5) PNW Plant Disease Management Handbook, 2001, Oregon State University.

(6) Schwartz, H.F, and S.K. Mohan, 1995, Compendium of Onion and Garlic Diseases, APS Press.

(7) PNW Insect Management Handbook, 2001, Oregon State University.

(8) PNW Weed Control Handbook, 2001, Oregon State University.

(9) Schreiber, A., and L. Richie, 1995, Washington Minor Crops, Washington State University.


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