WSU Extension

Hortsense

Caption: Aphid colony
Photo by: Unknown
  
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Mountain Ash : Aphids
(revision date: 2/14/2019)


Biology
Aphids are small, soft-bodied insects that typically feed near the tip of growing shoots. Their feeding may deform leaves (curling, distortion) and stunt terminal growth. Aphids range in size up to 1/8" long and often produce honeydew, a sweet sticky material. The honeydew may develop a growth of black sooty mold, which is an aesthetic problem but seldom harms the plant. It may also attract honeydew-feeding ants.
Management Options

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

Chemical Management


Apply when aphids or damage is first noticed. 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.
  • All Seasons Horticultural & Dormant Spray Oil Conc [Organic]
    Active ingredient: oil/pet distillate  |  EPA reg no: 4-80
  • R-T-U Year-Round Spray Oil
    Active ingredient: oil/pet distillate  |  EPA reg no: 6218-78
  • Safer Brand BioNEEM Multi-Purpose Insecticide & Repellent Conc [Organic]
    Active ingredient: azadirachtin  |  EPA reg no: 70051-6-42697
  • This list may not include all products registered for this use.
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Caption: Aphid colony
Photo by: Unknown
Caption: Aphid cast skins
Photo by: R.S. Byther