Disease Control

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

NOTE:  For the products for disease control listed below, one product trade name and formulation is provided for each active ingredient (common name) as an example of rates, days to harvest (dh), REI, and special instructions. In many cases there are other products available with the same active ingredient. Please see Table 22 and Alphabetical Listing by Trade Name for more information on products with the same active ingredients.

Blue Mold (Penicillium species)

Blue mold is a harvest and storage disease and may be particularly prevalent on fresh garlic. 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 borne in infected cloves or seed. Invasion is usually through wounds, mechanical bruises, or freezing injury. Control other diseases in the field to prevent avenues for infection. Harvest bulbs with a minimum or bruising and wounding and dry promptly. Store bulbs at 5° C (40° F) with low relative humidity. Some countries recommend treating with fungicides before storage.

thiophanate methyl (Thiophanate Methyl 85 WDG): 0.8 lb/gal. (REI 12h, Group 1 ). Pre-plant treatment.

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 plus thiram (Apron XL LS plus Thiram): 0.16 to 0.64 fl oz/100 lbs seed. (REI 48h, Groups 11 & M3). Seed treatment.

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 3-4 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.

azoxystrobin (Quadris): 9.0-15.5 fl oz/A (0 dh, REI 4h, Group 11). Make preventive applications on a 5-7 day schedule. Do not make more than one application of Quadris before alternating with fungicides that have a different mode of action.

copper hydroxide (Kocide 3000): 0.75 lb/A. (0 dh, REI 24h, Group M1). Can cause phytotoxicity to leaves.

dimethomorph (Forum): 6 oz/A (0 dh, REI 12h, Group 15). Forum must be applied as a tank mix with another fungicide that has a different mode of action. Apply in adequate water.

fenamidone (Reason 500 SC): 5.5 fl oz/A. ( 7 dh, REI 12h, Group 11). Do not make more than one application of Reason before alternating to a fungicide from a different resistance management group. Do not alternate with Quadris.

fluopicolide (Presidio): 3-4 fl oz/A. (2 dh, REI 12h, Group43). Must be applied in a tank mix with another labeled fungicide product with a different mode of action.

potassium salts of phosphorous acid (ProPhyt, Fosphite, Phostrol): Rates vary with formulation. (0 dh, 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.

mandipropamid (Revus): 8.0 fl oz/A. (7 dh, REI 12h, Group 40. Begin applications before disease development and continue on a 7-10 day interval. Make no more than two consecutive applications before alternating with a fungicide with a different mode of action.

mefenoxam and mancozeb (Ridomil Gold MZ): 2.5 lbs/A (7 dh, REI 48h, Groups 4 & 18). Use sufficient water to obtain thorough coverage. Begin applications when conditions are favorable for disease development and continue on a 14-day schedule. Do not apply Ridomil Gold more than four times.

Purple Blotch (Alternaria porri)

Practice long rotations with unrelated crops and practices that reduce hours of leaf wetness, i.e., plant spacing and good air drainage. Plant resistant or tolerant varieties. Plow under crop residues promptly after harvest. Use of a single fungicide throughout the growing season is not recommended.

azoxystrobin (Quadris): 6.0 to 12.0 fl oz/a (0 dh, REI 4h, Group 11). Apply at the first sign of disease and alternate with chlorothalonil after 7-14 days. Do not exceed three applications. Do not rotate with other Group 11 fungicides (Cabrio).

boscalid (Endura): 6.8 oz/A. (7 dh, REI 12h, Group 7). Begin applications prior to disease development and continue on a 7 to 14 day interval. Do not make more than two consecutive applications before rotating to a fungicide with a different mode of action.

chlorothalonil (Bravo Ultrex): 0.9 to 2.7 lb/A (7 dh, REI 12h, Group M5). When disease is present, use the higher rate.

maneb/mancozeb (Maneb, Penncozeb, Manzate, and Dithane): Rates vary depending on formulation. See label and Table 23. (7 dh, REI 24h, Group M3).

propiconazole (Tilt): 4-8 fl oz/A. (14 dh, REI 12h, Group 3).

pyraclostrobin (Cabrio EG): 8 to 12 oz/A (7 dh, REI 12h, Group 11). Apply at the first sign of disease and alternate with chlorothalonil after 7-14 days. Do not exceed six applications or 72 oz/A. Do not rotate with other Group 11 fungicides (Quadris).

pyraclostrobin plus boscalid (Pristine): 10.5-18.5 oz/A. (7 dh, REI 12h, Groups 11 plus 7). Begin applications prior to disease development. Do not make more than two applications of Pristine before alternating with a fungicide with a different mode of action. Do not alternate with Quadris, Cabrio, or other Group 11 fungicides.

pyrimethanil (SCALA SC Fungicide):  9.0-18 fl oz/a. (7 dh, REI 12h, Group 9). Use lower rate only in a tank mix with a broad spectrum fungicide.

Stem and Bulb Nematode (Ditylenchus dipsaci)

The nematode can be spread in infested soil, on equipment, and infected seed. Symptoms include erratic stands, stunting, looping and bending of leaves, twisting and growth deformities. Soft rot caused by secondary invaders such as bacteria, fungi, maggots, and larvae often occurs in infected bulbs. Ditylenchus dipsaci infects germinating seed or is borne in seed cloves. D. dipsaci can be controlled by four year crop rotations including the elimination of volunteer onions or garlic and host weeds. The primary treatment for controlling nematodes in garlic is hot water treatment of cloves. The standard regime is 30-45 minutes at 38° C (100° F), 20 minutes at 49° C (120°F), and then 10-20 minutes at 18-22° C (64-72° F). An alternative is the production of nematode free seed garlic cloves by meristem culture and isolated production. Various nematicides and fumigants have been used as soil treatments. 

White Rot (Sclerotium cepivorum)

Avoid planting in infested fields. Destroy infected plants and spot treat the soil around the plants with fumigants. Warm season production of host crops may greatly reduce sclerotial inoculum. Practice crop rotation. 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.

iprodione (Rovral): 4.0 lb/A.(REI 24 h, Group 2). Apply in-furrow at planting. Do not make more than one application per year.

PCNB (Terraclor): 27.5 lb/A. (REI 12 h, Group14). Apply in-furrow at planting. For clove treatment, use 13.5 lb/1,000 lb of seed cloves.