Click to print

Click to enlarge.

Beginner

Scientific Name
Botrytis cinerea

Identification
Wedge shaped, dark brown lesions with concentric rings which usually develop on the tips or margins of leaflets. Lesions are limited by major veins.

Dense, fuzzy greyish-brown fungal growth and spores are produced on the stems when the weather is wet. Affected stems become hollow.

The skin of infected tubers is wrinkled. Under the skin, tissues are soft and wet, but with time will darken and develop into a dry rot.

Often Confused With
Early blight
Late blight
Air pollution

Period of Activity
More common in wet years. It usually develops on lower leaves after the rows are closed

Scouting Notes

• Scouting should start before the rows close.
• Fields should be monitored at least twice a week.
• When walking fields, stop at many sites as possible and check plants at random.
• Always examine the lower part of the plants where initial infection starts.

Thresholds
Growers should make management decisions based on the level of disease incidence in the field.

Advanced

Scientific Name
Botrytis cinerea

Identification
Wedge shaped, dark brown lesions with concentric rings which usually develop on the tips or margins of leaflets. Lesions are limited by major veins.

Dense, fuzzy greyish-brown fungal growth and spores are produced on the stems when the weather is wet. Affected stems become hollow.

The skin of infected tubers is wrinkled. Under the skin, tissues are soft and wet, but with time will darken and develop into a dry rot.

Often Confused With
Early blight
Late blight
Air pollution

Biology
The fungus overwinters in the soil on dead leaves, vines or infected tubers. New infections can arise from spores produced on crop residues, from germinating propagules (sclerotia) or from spores produced on other hosts. Cool, humid conditions and dense crop canopies favour infection. Botrytis gray mold usually develop in Ontario in July-August when potato rows are usually closed and humidity is high in the lower part of the plants. The fungus penetrates leaves through wounds or through diseased tissues. It can infect damaged tubers at harvest, during transit or when grading.

Period of Activity
More common in wet years. It usually develops on lower leaves after the rows are closed

Scouting Notes

• Scouting should start before the rows close.
• Fields should be monitored at least twice a week.
• When walking fields, stop at many sites as possible and check plants at random.
• Always examine the lower part of the plants where initial infection starts.

Thresholds
Growers should make management decisions based on the level of disease incidence in the field.

Management Notes
Avoid crop stress:

• Provide adequate levels of nutrients.
• Manage other pests.
• Match irrigation with crop needs. Do not over-irrigate.
• Timely application of crop protection materials.
• Harvest tubers when the skin is set and avoid mechanical injury.