WSU Extension

Hortsense

Elm
 
Disease
Bacterial wetwood (Slime flux) 
Dutch elm disease 
Nectria canker 
Insect
Aphids 
Bark beetles 
Carpenterworm 
Elm leaf beetle 
Elm leafminer 
European elm scale 
Spiny elm caterpillar 



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Caption: Elm woolly aphid
Photo by: A.L. Antonelli
  
Elm : Aphids
(revision date: 2/14/2019)


Biology
Aphids are soft-bodied, pear-shaped insects that feed on the leaves. They are yellowish to green in color and approximately 1/16" long. Aphids often produce honeydew, a sweet, sticky substance which can develop a dark growth of black sooty mold. Deformed leaves are often associated with heavy infestations. Whitish cast skins are often found on leaves, as well. Some aphid species may also cause galls.
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 predatory 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

Thorough coverage of the foliage is important, including lower leaf surfaces. Apply when aphid build up is noticed. Apply oils in early spring before bud swell. 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
  • Bug Buster-O [Organic]
    Active ingredient: pyrethrins  |  EPA reg no: 1021-1771-54705
  • Hi-Yield Dormant Spray
    Active ingredient: oil/pet distillate  |  EPA reg no: 7401-428
  • Safer Brand BioNEEM Multi-Purpose Insecticide & Repellent Conc [Organic]
    Active ingredient: azadirachtin  |  EPA reg no: 70051-6-42697
  • Safer Brand Insect Killing Soap Conc II [Organic]
    Active ingredient: potassium laurate  |  EPA reg no: 42697-60
  • 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: Elm woolly aphid
Photo by: A.L. Antonelli