Walnut: Blight
categories: Tree Fruits Walnut Walnut Diseases
revision date: 2022-12-05 12:00
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
Use Integrated Pest Management (IPM) for successful plant problem management.
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: Visit Home and Garden Fact Sheets for more information on using pesticides.
- 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
Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.