WSU Extension

Hortsense

Caption: Elm leafminer damage
Photo by: J. O'Brien
  
print version| pdf version| email url    

Elm : Elm leafminer
(revision date: 3/10/2017)


Biology
Elm leafminers feed by removing green tissue from between upper and lower surfaces of the leaves. Symptoms of feeding by the yellowish or green larvae include large brown to gray brown blotches on the leaves. These damaged leaves may remain on the tree throughout the growing season. The adult elm leafminer is a small black sawfly. This pest attacks Scotch, Camperdown, English and American elm.
Management Options

Non-Chemical Management
  • Natural predators may help control populations.
  • Pinch, or pick and destroy, infested leaves to kill larvae.
Select non-chemical management options as your first choice!

Chemical Management


If you choose to use a pesticide, apply when mine blotches are first noticed or at least before late spring when larvae begin to leave the leaves to pupate in the soil. Insecticidal soaps must be applied to the exposed larvae. 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.
  • Bonide Captain Jack's Deadbug Brew R-T-U [Organic]
    Active ingredient: spinosad (spinosyn A+D)  |  EPA reg no: 4-472
  • Safer Brand Insect Killing Soap Conc II [Organic]
    Active ingredient: potassium laurate  |  EPA reg no: 42697-60
  • This list may not include all products registered for this use.
Images
    - hide images

+ Show larger images

 
Caption: Elm leafminer damage
Photo by: J. O'Brien
Caption: Elm leafminer damage
Photo by: A. L. Antonelli