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 25 and Fungicides and Bactericides Alphabetical Listing by Trade Name for more information on products with the same active ingredients.
The symbol OG indicates 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 cause 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)
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 seed-borne and soil-borne 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. 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): 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 14d, REI 12h, Groups 11 & M5. 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 (DoubleNickelOG): 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 (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 500): 1.0 pt/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 & 18. 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 7d, 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 14d, REI 12h, Groups 11 & M5. See label for tank mix precautions.
azoxystrobin plus difenoconazole (Quadris Top): 12.0 to 14.0 fl oz/A; PHI 1d, 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 LCOG): 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.
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.
famoxadone plus cymoxanil (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.
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 12h, Group 3.
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.
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 100º F, 20 minutes at 120º F, and then 10 to 20 minutes at 64º-72º F. 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 26 fl oz/A; PHI 14d, REI 12h, Group 11 & 3.
Bacillus amyloliquefaciens strain D747 (DoubleNickel 55OG): 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): 11.0 to 14.0 oz/A; PHI 7d, REI 12h, Groups 9 & 12.
fludioxonil (Cannonball WP): 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): 25.0 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.