What is it?

Birch leafminers are several species of sawflies that attack all species of birch trees. The larvae feeds between the surfaces of a leaf, causing mostly aesthetic problem to the tree.

Symptoms

• A small, light green or gray spots appear on the leaves around areas where eggs were deposited in early June
• An irregular shape of brown blotch appears and increases in size while the larvae is “mining”.
• Foliage turns brown and leaf’s edge might curl

Damages

• It is mainly aesthetic issue and seldom kill the tree.
• However, repeated attack can stress the tree and more prone to other pests and diseases.

What to do?

• Keep your birch tree as healthy as possible to withstand attack, by enough watering, fertilizing.
• Introduce natural enemies such as parasitic wasps.
• Rake and dispose fallen leaves in fall time.

Other resources:

https://tidcf.nrcan.gc.ca/en/insects/factsheet/7765

https://natural-resources.canada.ca/forest-forestry/insects-disturbances/birch-leafminer