Walnut: Walnut aphid

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

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

• 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.

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.

• 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.

Approved Pesticides

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.

• Bug Buster-O [Organic]
  Active ingredient: pyrethrins [EPA registration number: 1021-1771-54705]
• Monterey Bug Buster II
  Active ingredient: esfenvalerate [EPA registration number: 1021-1778-54705]
• Safer Brand BioNEEM Multi-Purpose Insecticide and Repellent Concentrate [Organic]
  Active ingredient: azadirachtin [EPA registration number: 70051-6-42697]
• Whitney Farms Insecticidal Soap [Organic]
  Active ingredient: potassium salts of fatty acid [EPA registration number: 67702-21-73327]
• This list may not include all products registered for this use.

Additional Images