Walnut: Blight
Photo by: R.S. Byther
Biology
Walnut blight is a bacterial disease affecting leaves, nuts, and other new growth including flowers. Bacteria are spread to new growth in the spring by rainy weather during the bloom season.
Leaves develop reddish-brown spots with a yellow halo. Leaves affected during expansion are typically distorted due to these lesions.
Twigs develop small black cankers and may be girdled and killed. Young nuts show a dark lesion at the blossom end and drop from the tree.
Nuts infected later in development have small, water-soaked spots on the husk which develop into sunken, cracked, black lesions. Nut kernels may be shriveled or of low quality.
The bacteria overwinter in buds and twig cankers and are spread by water, infecting through natural openings in plant tissues.
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!
- Plant disease-resistant varieties such as ‘Howe’ and ‘Spurgeon’. The variety ‘Franquette’ is highly susceptible to blight.
- Prune out and destroy infected tissues, when practical.
- Avoid overhead watering.
- Space trees and prune to provide good air circulation.
Chemical Management
IMPORTANT: Always read and follow label directions when working with pesticides.
For more information on using pesticides visit :
- Make fungicide applications when catkins begin to enlarge, when shoots begin to expand, and early postbloom.
- Homeowners should not make foliar applications to trees over 10 ft tall.
- Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.
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.
WSU Extension programs and employment are available to all without discrimination.
Evidence of noncompliance may be reported through your local Extension office.