Disease Control : New England Vegetable Management Guide : UMass Amherst

NOTE: For the disease control products listed below, one product trade name and formulation is provided for each active ingredient (common name) as an example of rates, preharvest interval (PHI), restricted entry interval (REI), and special instructions. In many cases, there are other products available with the same active ingredient. Please see Table 26 and Fungicides and Bactericides Alphabetical Listing by Trade Name for more information on products with the same active ingredients.

The symbol ^OGindicates a product is listed by the Organic Materials Review Institute (OMRI) as approved for use in organic production. See Organic Certification section for more detail.

The most common controls for leek and garlic diseases include the use of disease-resistant cultivars and pathogen-free seed and bulbs, as well as cultural practices including crop rotation and crop residue management that restrict the pathogens.

Blue Mold (Penicillium spp.)

Blue mold is typically most problematic as a storage disease, although it can infect seed cloves as well, and cause poor stands. Several Penicillium species cause blue mold, and these species are common in soil, on plant and animal debris, and in senescing plant tissues. Some species may be carried on infected cloves or seed. The mold presents as a mass of blue-gray fungal growth on the bulb, and in the field, yellowed and stunted plants may be observed. These pathogens typically invade bulbs through wounds, mechanical bruises, or freezing injury. Control other diseases in the field to prevent avenues for infection. Harvest bulbs with a minimum of bruising and wounding, and dry promptly. Store bulbs at 40°F with low relative humidity. Some countries recommend treating with fungicides before storage.

thiophanate methyl (Topsin M 70WP): 1.0 lb/100 gal; REI 72h, Group 1. Pre-plant treatment by immersion of garlic cloves in suspension for at least 5 minutes.

Damping-off and seed rot (Pythium and Rhizoctonia)

Damping- off and seed rot are commonly caused by Pythium spp. from poor soil draining conditions. Seeds and roots of infected seedlings will appear water- soaked, then will decompose. Symptoms of plants infected after the seedling stage will show foliar damage, leaves yellowing from tip to base. Avoid excessive soil moisture by improving soil drainage or planting on raised beds. Seed and soil treatments with fungicides are a recommended practice.

mefenoxam (Apron XL): 0.085 to 0.64 fl oz/100 lbs seed; REI 48h, Group 4. Not effective for Rhizoctonia.
fludioxonil (Maxim 4FS): 0.08 to 0.16 oz/100 lb seed; REI 12h, Group 12. For protection against seedborne and soilborne fungi. Does not control Pythium or Phytophthora.

Downy Mildew (Peronospora destructor)

During extended periods of cool, humid weather, this disease can be highly destructive, causing losses in both yield and bulb quality. Symptoms can be seen as a grayish violet furry growth on the surface of the leaf or seed stem. Affected leaves will become a pale green to yellow. Practice a 3- to 4-year rotation. Plant on well-drained soil and orient rows in the same direction as prevailing winds. Avoid overhead irrigation. A regular program of fungicide spraying based on climatic conditions and disease forecasts should be followed.

ametoctradin plus dimethomorph (Zampro): 14.0 fl oz/A; PHI 0d, REI 12h, Groups 45 and 40.
azoxystrobin (Quadris Fowable_Sygenta): 9.0 to 15.5 fl oz/A; PHI 0d, REI 4h, Group 11. Do not make more than 1 application of Quadris before alternating with fungicides that have a different mode of action.
azoxystrobin plus chlorothalonil (Quadris Opti): 2.4 to 3.6 pt/A; PHI 7d, REI 12h, Groups 11 & M. See label for tank mix precautions.
azoxystrobin plus propiconazole (Quilt Xcel): 17.5 to 21 fl oz/A; PHI 14d, REI 12h, Group 11 & 3.
Bacillus amyloliquefaciens strain D747 (DoubleNickel LC^OG): 0.25 to 3.0 lb/A; PHI 0d, REI 4 h, Group 44. Disease suppression only. For improved control; mix or rotate with a chemical fungicide.
copper hydroxide (Kocide 3000): 0.75 to 1.5 lb/A; PHI 0d, REI 48h, Group M1. Can cause phytotoxicity to leaves.
dimethomorph (Forum): 6.0 fl oz/A; PHI 0d, REI 12h, Group 40. Forum must be applied as a tank mix with another fungicide that has a different mode of action. Apply in adequate water.
famoxadone plus cymoxanil (DuPont Tanos): 8.0 oz/A; PHI 3d, REI 12h, Groups 11 & 27. Must be tank mixed with an appropriate contact fungicide with a different mode of action. Do not alternate or tank mix with other Group 11 fungicides.
fenamidone (Reason 500 SC): 5.5 fl oz/A; PHI 7d, REI 12h, Group 11. Do not make more than one application of Reason before alternating to a fungicide from a different resistance management group
fluazinam (Omega 500F): 16 fl oz./A; PHI 7d, REI 12h, Group 29. Use sufficient water for thorough coverage, but not less than 5 gal./A.
mancozeb (Dithane F45): 2.4 qt/A; PHI 7d, REI 24h, Group M3.
mandipropamid (Revus): 8.0 fl oz/A; PHI 7d, REI 4h, Group 40.
mefenoxam plus chlorothalonil (Ridomil Gold Bravo SC): 2.5 pt/A; PHI 7d, REI 48h, Groups 4 & M5.
mefenoxam and mancozeb (Ridomil Gold MZ): 2.5 lbs/A; PHI 7d, REI 48h, Groups 4 & M3. Use sufficient water to obtain thorough coverage. Do not apply Ridomil Gold more than 4 times.
oxathiapiprolin & mandipropamid (Orondis Ultra): 5.5 to 8.0 fl oz/A; PHI 7d, REI 4h, Group 49 & 40.
phosphorous acid (Fosphite): 1.0 to 3.0 qt/in a minimum of 20 gal/A; PHI 0d, REI 4h, Group 33. Do not apply to plants that heat or moisture stressed. Do not apply directly to copper treated plants within 20-day interval to avoid plant injury.
pyraclostrobin (Cabrio EG): 12.0 oz/A; PHI 7d, REI 12h, Group 11. Do not rotate with other Group 11 fungicides.

Bulb and Basal Plate Rot (Fusarium spp.)

Bulb and basal plate rot of garlic is caused by Fusarium culmorum and F. roseum. Symptoms include pre-emergence decay of cloves and seedlings, decay of the stem plate and storage leaves during the growing season, and postharvest decay of cloves in stored bulbs. Infected cloves will have sunken, circular brown lesions on their outer surface and/or basal plate. Foliar symptoms include curving, yellowing and necrosis of leaves beginning at tips, and wilt. Infection occurs mainly from the soil through the stem plate. Incidence of the disease increases with injury by onion maggot or other insects. Cloves may remain infected but non-symptomatic. The pathogen is disseminated in seed, soil, infected debris, and irrigation water. Hot water seed treatment has reduced garlic clove infection by 50%, but is not enough to provide commercially-acceptable control when clove infection is severe. Excess soil N favors Fusarium infection; take care to account for soil organic matter and cover crop N credits and not to over apply fertility. Long (4-year) rotations to non-susceptible crops may minimize losses. Storage at 40°F also helps. The most important control measure is the planting of resistant cultivars.

Purple Blotch (Alternaria porri)

Alternaria porri is most likely to become problematic when temperatures are warm (77-85°F) with high humidity. Small lesions will form on stems or leaves, eventually enlarging and becoming tan or purple. Purple blotch is easily confused with Stemphylium leaf blight, which tends to produce darker lesions. While laboratory diagnoses are needed for proper identification, these two pathogens can be managed in the same way. Practice long rotations with unrelated crops, and use practices that reduce hours of leaf wetness, e.g. plant spacing and good air drainage. Plant resistant or tolerant varieties. Plow under crop residues promptly after harvest. Rotate fungicides throughout the growing season.

azoxystrobin (Quadris): 6.0 to 12.0 fl oz/A; PHI 0d, REI 4h, Group 11. Do not rotate with other Group 11 fungicides.
azoxystrobin plus chlorothalonil (Quadris Opti): 1.6 to 3.2 pt/A; PHI 7d, REI 12h, Groups 11 & M. See label for tank mix precautions.
azoxystrobin plus difenoconazole (Quadris Top): 8 to 14 fl oz/A; PHI 7d, REI 12h, Groups 11 & 3.
azoxystrobin plus propiconazole (Quilt): 14.0 to 27.5 fl oz/A; PHI 14d, REI 12h, Group 11 & 3.
Bacillus amyloliquefaciens strain D747 (DoubleNickel LC^OG): 0.25 to 3.0 lb/A; PHI 0d, REI 4 h, Group 44. Disease suppression only. For improved control; mix or rotate with a chemical fungicide.
boscalid (Endura): 6.8 oz/A; PHI 7d, REI 12h, Group 7. Do not make more than 2 consecutive applications before rotating to a fungicide with a different mode of action.
chlorothalonil (Bravo Weather Stik): 1.0 to 3.0 pt/A; PHI 7d, REI 12h, Group M5. When disease is present, use the higher rate.
chlorothalonil & oxathiapiprolin (Orondis Opti): 1.75 to 2.5 pt/A; PHI 7d, REI 12h, Groups 49 & M05.
chlorothalonil & zoxamide (Zing): 30.0 fl oz/A; PHI 7d, REI 12h, Groups 22 & M05. Do not apply to exposed bulbs.
copper hydroxide (Kocide 3000): 0.75 to 1.5 lb/A; PHI 0d, REI 48h, Group M1. Do not apply in a spray solution having a pH less than 6.5 or tank mix with Aliette.
cyprodinil plus fludioxonil (Switch 62.5 WG): 11.0 to 14.0 oz/A; PHI 7d, REI 12h, Groups 9 & 12. Do not make more than 2 consecutive applications before rotating to a fungicide with a different mode of action.
difenoconazole plus cyprodinil (Inspire Super): 16.0 to 20.0 fl oz/A; PHI 7d, REI 12h, Group 3 & 9. Apply in sufficient volume to achieve thorough coverage.
difenoconazole plus fluopyram (Luna Flex): 10.0 to 13.6 fl oz/A; PHI 7d, REI 12h, Groups 3 & 7.
famoxadone plus cymoxanil (DuPont Tanos): 8.0 oz/A; PHI 3d, REI 12h, Groups 11 plus 27. Must be tank mixed with an appropriate contact fungicide with a different mode of action. Do not alternate or tank mix with other Group 11 fungicides.
fenamidone (Reason 500 SC): 5.5 fl oz/A; PHI 7d, REI 12h, Group 11. Do not rotate with other Group 11 fungicides.
fluazinam (Omega 500DF): 16.0 fl oz/A; PHI 7d, REI 12h, Group 29. Do not make more than 6 applications per acre per year. Do not use an adjuvant.
fluopyram (Velum Prime): 6.5 to 6.84 fl oz/A; PHI 30d, REI 12h, Group 7. Note longer PHI.
penthiopyrad (Fontelis): 16.0 to 24.0 oz/A; PHI 3d, REI 12h, Group 7.
mancozeb (Dithane F45): 2.4 qt/A; PHI 7d, REI 24h, Group M3.
polyoxin D (OSO 5%SC): 3.75 to13.0 fl oz/A; PHI 0d, REI 4h, Group 19.
propiconazole (Tilt): 4.0 to 8.0 fl oz/A; PHI 14d, REI 24h, Group 3.
Pseudomonas chlororaphis strain AFS009 (Howler EVO^OG): 40.0 to 120.0 oz/A; PHI 0d, REI 4h, Group BM02. May be used in greenhouse.
pydiflumetofen plus fludioxonil (Miravis Prime): 11.4 fl oz/A; PHI 7d, REI 12h, Groups 12 & 7. Apply in sufficient volume to achieve thorough coverage.
pyraclostrobin (Cabrio EG): 8.0 to 12.0 oz/A; PHI 7d, REI 12h, Group 11. Do not rotate with other Group 11 fungicides (Quadris).
pyraclostrobin plus boscalid (Pristine): 10.5 to 18.5 oz/A; PHI 7d, REI 12h, Groups 11 & 7. Do not make more than 2 applications of Pristine before alternating with a fungicide with a different mode of action.
pyrimethanil (Scala SC Fungicide): 18.0 fl oz/A; PHI 7d, REI 12h, Group 9.
pyrimethanil plus fluopyram (Luna Tranquility): 16.0 to 27.0 fl oz/A; PHI 7d, REI 12h, Groups 9 & 7.

Bloat Nematode (Ditylenchus dipsaci)

Ditylenchus dipsaci is a nematode species that infects germinating garlic seed and is primarily borne in seed cloves. The nematode itself has limited mobility, but can be easily spread in infested soil, on equipment, and in infected seed and plant material. D. dipsaci is common in all temperate regions. It is an obligate parasite of plants; populations of the nematode exhibit marked host preferences. The nematodes aggregate into a mass called nematode wool and with slow drying can persist in infested fields for long periods. Symptoms of garlic bloat include leaf yellowing, erratic stands, stunting, looping and bending of leaves, twisting, and growth deformities. Bulb damage can be mistaken for Fusarium basal plate rot with decay occurring both at the neck and the basal plate. Infected bulbs will lack roots. D. dipsaci can be controlled with long crop rotations including the elimination of volunteer onions, garlic, and host weeds. The primary method of controlling nematodes is hot water treatment of seed cloves. The standard regime is 30 to 45 minutes at 100ºF, 20 minutes at 120ºF, and then 10 to 20 minutes at 64-72ºF. Hot water treatment must be performed carefully to prevent damage to cloves. Chemical, physical, and cultural methods have been used to restrict damage, but most chemical treatments are no longer registered for use.

White Rot (Sclerotium cepivorum)

White rot is caused by Sclerotium cepivorum, which persists for a long time in soil. It is “activated” by root exudates produced by Allium crops. Affected plants will show yellowing older leaves and stunting, and small black sclerotia can be seen on the bulb. Disease development is favored by cool, moist soil conditions. There is little to be done once a field is infested with S. cepviorum, and crops should be rotated out of Alliums for as long as possible. Some fungicides (Iprodione) provide protection for the establishment of garlic, but fungicide control is marginal for full-season crops. Soil fumigation may provide partial control. In general, neither fungicides nor fumigation have provided consistent, reliable, full-season control of white rot. Hot water treatment of garlic seed can reduce the potential to spread white rot sclerotia. Winter flooding and soil solarization can reduce the number of sclerotia. White rot symptoms are less severe on leeks.

azoxystrobin plus propiconazole (Quilt Xcel): 17.5 to 21 fl oz/A; PHI 14d, REI 12h, Group 11 & 3.
Bacillus amyloliquefaciens strain D747 (DoubleNickel 55^OG): 0.12 to 1.0 lb/A as a soil drench; PHI 0d, REI 4 h, Group 44.
boscalid (Endura): 6.8 oz/A; PHI 7d, REI 12h, Group 7. Apply in-furrow at planting.
cyprodinil plus fludioxonil (Switch 62.5 WG): 7 to 14 oz/A; PHI 7d, REI 12h, Groups 9 & 12.
fludioxonil (Cannonball WG): 0.5 oz/1000 ft.; PHI 7d, REI 12h, Group 12. Apply in-furrow at planting.
iprodione (Rovral): 4.0 pt/A; REI 24h, Group 2. Apply in-furrow at planting. Do not make more than 1application per year.
tebuconazole (Orius 3.6F): 20.5 fl oz/A; PHI 7d, REI 12h, Group 3. Apply in-furrow at planting or over the top in a 4 to 6 inch band.
thiophanate methyl (Topsin M 70WP): 2.0 lb/A; REI 72h, Group 1. Apply in furrow.

Botrytis Neck Rot (Botrytis spp.)

The disease is limited to the allium family and also causes neck rot of onion, leeks, and shallots. The pathogen is soil- and seed-borne and is readily spread through planting of infected gloves or seed. Botrytis rot primarily appears after harvest in garlic that is not cured or stored correctly. Under moist conditions, a gray mold may develop on the surface of or between garlic scales and later distinct black sclerotia (overwintering, dense mass of fungal mycelia) appear around the rotting neck. These sclerotia germinate in spring and release thousands of spores, which can be wind-carried to susceptible host plants, starting new disease cycles. Initial symptoms of the disease may appear near the soil line on garlic necks as the pathogen penetrates the tissue directly or via a wound, it then moves along the neck causing water soaked lesions. Under warm and wet conditions, the disease progresses quickly. Plant disease free cloves and minimize bruising or mechanical injury, especially during harvest and topping. Avoid excessive nitrogen application, which delays crop maturity and curing. Inspect plants for symptoms and signs of disease during the season as well as at harvest since plants may become infected in the field but will remain symptomless until they are in storage. Practice crop rotation and destroy and remove crop residue after harvest.

azoxystrobin plus difenoconazole (Quadris Top): 12.0 to 14.0 fl oz/A; PHI 1d, REI 12h, Groups 11 & 3.
Bacillus amyloliquefaciens strain D747 (Double Nickel 55^OG): 0.25 to 3.0 lb/A; PHI 7d, REI 4h, Group BM02.
chlorothalonil (Echo 720): 1.0 to 3.0 pt/A; PHI 14d, REI 12h, Group M05.
chlorothalonil & oxathiapiprolin (Orondis Opti): 1.75 to 2.5 pt/A; PHI 7d, REI 12h, Groups 49 & M05.
chlorothalonil & zoxamide (Zing): 30.0 fl oz/A; PHI 7d, REI 12h, Groups 22 & M05. Do not apply to exposed bulbs.
copper octanoate (Cueva): 38.0 gal/A (112 fl oz/1000 sq ft); PHI 0d, REI 4h, Group M01.
cyprodinil (Vangard WG): 10.0 oz/A; PHI 7d, REI 12h, Group 9. Thorough plant coverage is essential.
cyprodinil plus fludioxonil (Switch 62.5 WG): 11.0 to 14.0 oz/A; PHI 0d, REI 12h, Groups 9 & 12. Labeled for suppression of Botrytis neck rot.
difenoconazole plus cyprodinil (Inspire Super): 16.0 to 20.0 fl oz/A; PHI 7d, REI 12h, Groups 3 & 9. Apply in sufficient volume to achieve thorough coverage.
difenoconazole plus fluopyram (Luna Flex): 10.0 to 13.6 fl oz/A; PHI 7d, REI 12h, Groups 3 & 7.
fluazinam (Omega 500DF): 16.0 fl oz/A; PHI 7d, REI 12h, Group 29. Do not make more than 6 applications per acre per year. Do not use an adjuvant.
hydrogen peroxide plus peroxyacetic acid (Oxidate 2.0^OG): see label for rates; PHI 0d, REI 1h, Group NC.
laminarin (Vacciplant): 14.0 to 22.0 fl oz/A; PHI 0d, REI 4h, Group P04.
penthiopyrad (Fontelis): 16.0 to 24.0 oz/A; PHI 3d, REI 12h, Group 7.
Pseudomonas chlororaphis strain AFS009 (Howler EVO^OG): 40.0 to 120.0 oz/A; PHI 0d, REI 4h, Group BM02. May be used in greenhouse.
pydiflumetofen plus fludioxonil (Miravis Prime): 11.4 fl oz/A; PHI 7d, REI 12h, Groups 12 & 7. Apply in sufficient volume to achieve thorough coverage.
pyraclostrobin (Cabrio EG): 12.0 oz/A; PHI 7d, REI 12h, Group 11. For disease suppression only.
pyraclostrobin plus fluxapyroxad (Merivon Xemium): 8.0 to 11.0 fl oz/A; PHI 7d, REI 12h, Groups 11 & 7. Do not apply more than 2 consecutive applications before switching to a labeled non-Group 7 or non-Group 11 fungicide.
pyrimethanil plus fluopyram (Luna Tranquility): 16.0 to 27.0 fl oz/A; PHI 7d, REI 12h, Groups 9 & 7.
Streptomyces lydicus strain WYEC 108 (Actinovate^OG): 3.0 to 12.0 oz/A; PHI 0d, REI 4h, Group BM02.
tebuconazole plus fluopyram (Luna Experience): 8.0 to 12.8 fl oz/A; PHI 7d, REI 12h, Groups 3 & 7.

Stemphylium Leaf Blight (Stemphylium sp.)

The disease has a broad host range including garlic, leek, onion, shallot, asparagus, tomato, radish, sunflower, parsley, alfalfa, and soybean. Symptoms appear as small, tan to brown lesions on the leaves which rapidly progress to defoliate plants. A decrease in photosynthetic leaf area results in smaller and reduced quality of bulbs, and indirectly, poor shelf and storage life. The recent emergence of the pathogen has been associated with the development of resistance to single-site mode-of-action fungicides, including strobilurins. Crop rotation to a non-host for at least one year may significantly reduce inoculum density. Additionally, post-harvest residue removal is an important means to promote degradation and overwintering of inoculum between seasons. Weed control and use of certified seed and clean transplants for field establishment are essential.

azoxystrobin plus difenoconazole (Quadris Top): 12.0 to 14.0 fl oz/A; PHI 1d, REI 12h, Groups 11 & 3.
cyprodinil plus fludioxonil (Switch 62.5 WG): 11.0 to 14.0 oz/A; PHI 0d, REI 12h, Groups 9 & 12.
difenoconazole plus benzovindiflupyr (Aprovia Top): 10.5 fl oz/A; PHI 7d, REI 12h, Groups 7 & 3. Do not make more than 2 consecutive applications before switching to a non-Group 7 fungicide.
difenoconazole plus cyprodinil (Inspire Super): 16.0 to 20.0 fl oz/A; PHI 7d, REI 12h, Groups 3 & 9. Apply in sufficient volume to achieve thorough coverage.
difenoconazole plus fluopyram (Luna Flex): 10.0 to 13.6 fl oz/A; PHI 7d, REI 12h, Groups 3 & 7.
laminarin (Vacciplant): 14.0 to 22.0 fl oz/A; PHI 0d, REI 4h, Group P04.
penthiopyrad (Fontelis): 16.0 to 24.0 oz/A; PHI 3d, REI 12h, Group 7.
Pseudomonas chlororaphis strain AFS009 (Howler EVO^OG): 40.0 to 120.0 oz/A; PHI 0d, REI 4h, Group BM02. May be used in greenhouse.
pydiflumetofen plus fludioxonil (Miravis Prime): 10.3 to 11.4 fl oz/A; PHI 7d, REI 12h, Groups 12 & 7. Apply preventatively in sufficient volume to ensure good coverage.
pyraclostrobin plus fluxapyroxad (Merivon Xemium): 5.5 to 11.0 fl oz/A; PHI 7d, REI 12h, Groups 11 & 7. Do not apply more than 2 consecutive applications before switching to a labeled non-Group 7 or non-Group 11 fungicide.
pyrimethanil plus fluopyram (Luna Tranquility): 16.0 to 27.0 fl oz/A; PHI 7d, REI 12h, Groups 9 & 7.
tebuconazole plus fluopyram (Luna Experience): 12.8 fl oz/A; PHI 7d, REI 12h, Groups 3 & 7.
thyme oil (Guarda): see label for rates; PHI 0d, REI 0h, Group NC.

Disease Control