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 leaf beetles
Photo by: Unknown
  
Elm : Elm leaf beetle
(revision date: 2/14/2019)


Biology
Elm leaf beetles feed on the leaves both as larvae and as adults. The larvae appear in late spring (typically May-June) from eggs laid by overwintering adults. The 1/4" larvae are greenish or yellow with black stripes and spots. They skeletonize leaves, feeding on the underside and eating all parts except the veins and upper cuticle, which turn brown. Adult elm leaf beetles are approximately 1/4" long and yellow to greenish with two dark stripes. Older adults are darker. Adult feeding causes small holes in the leaves. Severe infestations may result in severe premature leaf loss. Trees may releaf in late summer. Repeated infestations may weaken or kill trees. Weakened trees are also more susceptible to attack by elm bark beetles, which can carry the Dutch elm disease fungus.
Management Options


Non-Chemical Management
  • Plant resistant cultivars of American elm (Ulmus americana) including 'Dynasty', 'Princeton', 'Prospector', 'Frontier', and 'Pathfinder' (NOTE: Many American elm cultivars are highly susceptible to Dutch elm disease.)
  • Other elms reported to be somewhat resistant to elm leaf beetle feeding include Chinese (U. parvifolia) and the elm-like zelkovas (Zelkova spp.)
  • Provide proper culture to maintain plant health. Healthy plants are more tolerant of insect damage.
  • Prune dead and dying branches in late fall or winter.
Select non-chemical management options as your first choice!

Chemical Management

Apply when first larval damage appears. 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.
  • 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.
Images

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Caption: Elm leaf beetles
Photo by: Unknown