Walnut: Anthracnose (Blotch)
categories: Tree Fruits Walnut Walnut Diseases
revision date: 2022-12-05 12:00
Photo by: R.S. Byther
Biology
Anthracnose or blotch of walnut is caused by a fungus. The disease affects leaves, young twigs, and nuts. Leaves develop irregularly circular reddish-brown to grayish-brown spots up to 3⁄4″ across. Severe infections on sensitive cultivars can result in significant leaf drop. On twigs of the current season’s growth, anthracnose causes sunken grayish lesions with reddish-brown margins. Fruiting bodies may be visible in the lesion. Nuts develop sunken spots on the husks. These spots are typically smaller than the spots on the leaves. Infections that occur early in nut development often cause premature drop and reduction in yield. The fungus overwinters in infected plant debris and in twig lesions.
Management Options
Use Integrated Pest Management (IPM) for successful plant problem management.
Non-chemical Management
Select non-chemical management options as your first choice!
- Avoid susceptible varieties such as ‘Adams’.
- Rake up and destroy fallen leaves and nuts.
- Prune out infected twigs when practical.
Chemical Management
IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.
- Make applications to protect new growth when the disease has been a serious problem in previous years.
- 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.