WSU Extension


Onions, Garlic
Basal rot 
Downy mildew 
Gray mold 
Neck rot 
White rot 
Onion maggot 
Onion thrips 

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Caption: Botrytis gray mold on onion
Photo by: R.S. Byther
Onions, Garlic : Gray mold
(revision date: 6/3/2014)

Gray mold is a fungal disease primarily found on garlic. It attacks the tissues of the neck and bulb and occasionally causes a leaf blight. Symptoms of infection typically appear on the neck around the time of harvest, when tissues take on a water-soaked appearance with yellow discoloration. A gray, fuzzy mold develops between the scales, and small black fungal structures may be present around the neck. Gray mold eventually results in a rot of the bulbs. Infection typically occurs at the neck or through wounds in the bulb. Plantings that are in heavy, damp soil or that are overwatered have the greatest risk of infection. The disease often develops in stored bulbs and is favored by high humidity. The fungus causing gray mold can overwinter in the soil.
Management Options

Non-Chemical Management
  • Plant disease-free materials.
  • Rotate crops. Do not plant garlic and related crops in the same locations each year.
  • Do not overwater.
  • Do not overfertilize. Excess nitrogen results in delayed maturing of plants and greater susceptibility to disease.
  • Allow tops to mature before harvest.
  • Cure bulbs 6-10 days prior to storage.
  • Minimize bruising and injury during harvest.
  • Store bulbs in cool, dry, well-ventilated locations.
  • Pull out and discard or destroy diseased plants. Do not compost diseased materials.
Select non-chemical management options as your first choice!

Chemical Management

Apply at first sign of leaf blight disease and repeat at 7- to 10-day intervals. Do not apply more than 3 times per season on green onions, leeks, or shallots. Fungicides do not consistently control the bulb and neck rot diseases.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • Bonide Fung-onil Multi-Purpose Fungicide Conc
    Active ingredient: chlorothalonil  |  EPA reg no: 60063-9-4
  • GardenTech Daconil Fungicide Conc
    Active ingredient: chlorothalonil  |  EPA reg no: 67572-82-71004
  • Ortho Max Garden Disease Control Conc
    Active ingredient: chlorothalonil  |  EPA reg no: 239-2522
  • This list may not include all products registered for this use.

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Caption: Botrytis gray mold on onion
Photo by: R.S. Byther