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 



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Caption: Green peach aphid
Photo by: Unknown
  
Walnut : Walnut aphid
(revision date: 3/10/2017)


Biology
Walnut aphids are small, pale yellow, pear-shaped insects. They are typically found on the undersides of leaves. A second aphid species common on walnuts is the dusky-veined aphid, a grayish aphid found on upper leaf surfaces, usually in clusters along the midvein. Both species produce honeydew, a sweet, sticky material which may attract ants or become covered with a growth of dark sooty mold. Honeydew causes the husks to turn black on some walnut cultivars. Heavy infestations of aphids can cause wilting and leaf drop and weaken trees. Severe leaf loss also increases chances of sunburn damage to nuts.
Management Options


Non-Chemical Management
  • Encourage natural enemies including ladybird beetles, lacewings, syrphid (hover) fly larvae, and parasitic wasps. Avoid use of broad-spectrum insecticides which kill beneficial insects.
  • Hand-wipe or prune to control small, localized infestations when practical.
  • Wash aphids from tree with a strong stream of water.
  • Control honeydew-feeding ants, which may protect aphid colonies from predators.
  • Provide proper nutrition. High levels of nitrogen encourage aphid reproduction. Switch to a slow-release or low-nitrogen fertilizer.
Select non-chemical management options as your first choice!

Chemical Management

Apply only if aphids are in large numbers causing damage. Do not apply during bloom. Esfenvalerate is toxic to bees. Do not apply products containing esfenvalerate on or near blooming plants. To minimize risk to bees, apply in the evening after bees have stopped foraging for the day. 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.
  • Bayer Advanced Natria Neem Oil RTU/Roses, Flowers, Fruits & Vegetables [Organic]
    Active ingredient: clarified hydrophobic extract of neem oil  |  EPA reg no: 70051-13-72155
  • Bug Buster-O [Organic]
    Active ingredient: pyrethrins  |  EPA reg no: 1021-1771-54705
  • Monterey Bug Buster II
    Active ingredient: esfenvalerate  |  EPA reg no: 1021-1778-54705
  • Safer Brand BioNEEM Multi-Purpose Insecticide & Repellent Conc [Organic]
    Active ingredient: azadirachtin  |  EPA reg no: 70051-6-42697
  • Safer Brand Insect Killing Soap with Seaweed Extract II [Organic]
    Active ingredient: potassium laurate  |  EPA reg no: 42697-59
  • This list may not include all products registered for this use.
Images

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Caption: Green peach aphid
Photo by: Unknown
Caption: Aphid colony
Photo by: A.L. Antonelli
Caption: Aphid cast skins
Photo by: R.S. Byther