Birch: Birch leafminer
Photo by: A.L. Antonelli
Biology
The birch leafminer is the larvae of a small (about 1/8″-3/8″) black sawfly. The adult sawfly lays eggs in new leaves.
The larvae emerge and feed in leaf tissues, leaving blotch-shaped or winding brown mines. Mature larvae are flattened and may be up to 1/2″ long.
Larvae drop to the ground and pupate in the soil for two to three weeks before emerging as adults. There may be up to four generations per year, depending on length of growing season.
Vigorous gray, white, and paper birches are most commonly attacked. Repeated severe infestations may result in decline of trees.
Management Options
See "Using Integrated Pest Management (IPM) in the Landscape" for successful problem management techniques.
Non-chemical Management
Select non-chemical management options as your first choice!
- Plant resistant species and cultivars, including Betula davurica, B. jacquemontii, B. nigra, and the variety ‘Crimson Frost’.
- Pinch leaves to kill larvae in minor infestations on small trees.
- Reported as 95% resistant (B. costata, B. maximowicziana, B. populifolia x pendula ‘Purple Rain’, and B. schmittii).
- Natural predators may help control populations. Encourage predators such as green lacewings and spiders.
Chemical Management
IMPORTANT: Always read and follow label directions when working with pesticides.
For more information on using pesticides visit :
- If you choose to use a pesticide, apply when first leaves are fully formed, usually around May 1st.
- Make a second application from mid-June to mid-July.
- Insecticide products are toxic to bees.
- 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
If you choose to use a pesticide, some examples of products that are legal in Washington are listed below. Some products are labeled for just INDOOR or just OUTDOOR use, or may allow both uses. Be sure to choose a product appropriate for your situation. Always read and follow all label directions.
WSU Extension programs and employment are available to all without discrimination.
Evidence of noncompliance may be reported through your local Extension office.