WSU Extension

Hortsense

Walnut
 
Disease
Anthracnose (Blotch) 
Blackline 
Blight 
Thousand cankers disease 
Insect
European fruit lecanium 
Walnut aphid 
Walnut blister mite 
Walnut husk fly 
Walnut twig beetle 



print version| pdf version| email url    
Caption: Walnut anthracnose
Photo by: R.S. Byther
  
Walnut : Anthracnose (Blotch)
(revision date: 4/11/2018)


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

Non-Chemical Management
  • Avoid susceptible varieties such as 'Adams'.
  • Rake up and destroy fallen leaves and nuts.
  • Prune out infected twigs when practical.
Select non-chemical management options as your first choice!

Chemical Management

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.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • Bonide Liquid Copper Fungicide Conc/Organic Gardening
    Active ingredient: copper octanoate  |  EPA reg no: 67702-2-4
  • Monterey Liqui-Cop Copper Fungicidal Garden Spray
    Active ingredient: copper-ammonia complex  |  EPA reg no: 54705-7
  • Soap-Shield Flowable Liquid Copper Fungicide [Organic]
    Active ingredient: copper octanoate  |  EPA reg no: 67702-2-56872
  • This list may not include all products registered for this use.
Images

+ Show larger images

 
Caption: Walnut anthracnose
Photo by: R.S. Byther