Grape: Botrytis bunch rot (Gray mold)

• Categories: Grape Grape Diseases Small Fruits
• Last review date: 2026-05-15 06:20

Biology

This fruit rot is caused by a fungus which also causes disease in strawberries, raspberries, and many other plants. In grapes, the disease is typically limited to fruit. infection may occur throughout the season and in storage. Early-season infections often occur through the flower. A characteristic, fuzzy, gray-brown coating of fungal growth develops on the young fruit, which may later dry into infected mummies.

Later infections may develop as a result of rain during harvest, causing a condition known as “slip-skin”. Brownish patches develop on the fruit and the skin separates from the flesh. After harvest, storage rot may cause a brown, soft rot of the fruit.

The fungus overwinters on old cluster stems, canes, or mummified, diseased fruit. Disease development is favored by tight fruit clusters, dense foliage, and cool, moist conditions.

Management Options

See "Using Integrated Pest Management (IPM) in the Landscape" for successful problem management techniques.

Non-chemical Management

Select non-chemical management options as your first choice!

• Space plantings and prune to provide good air circulation and reduce humidity.
• Avoid overhead watering and other practices which cause moist conditions in the canopy.
• Prevent injury to the fruit, which can facilitate disease development.
• Clean up plant debris, including mummified fruit. Destroy or discard (do not compost) diseased materials.

Chemical Management

• Apply at beginning of fruit set after bloom is gone.
• Make 2 or 3 additional applications at 10- to 14- day intervals up to 3 weeks prior to harvest or when weather dries.
• Copper products offer only slight control.

Approved Pesticides

If you choose to use a pesticide, some examples of products that are legal in Washington are listed below. Some products are labeled for just INDOOR or just OUTDOOR use, or may allow both uses. Be sure to choose a product appropriate for your situation. Always read and follow all label directions.

• Bonide Copper Fungicide Spray or Dust RTU [Organic]
  Active ingredient: basic copper sulfate
  EPA registration number: 4-58
• Bonide Liquid Copper Fungicide Concentrate/Organic Gardening
  Active ingredient: copper octanoate
  EPA registration number: 67702-2-4
• Monterey Horticultural Oil [Organic]
  Active ingredient: mineral oil/pet distillate light
  EPA registration number: 48813-1-54705
• Soap-Shield Flowable Liquid Copper Fungicide [Organic]
  Active ingredient: copper octanoate
  EPA registration number: 67702-2-56872
• This list may not include all products registered for this use.