Birch Leafminer: a major issue of Birch tree in Calgaryby mrgadmin on April 22, 2023

Birch leafminer is one of the most common leaf problems in Calgary and surrounding areas. The adult fly is a small, black and 4-winged insect. It is active between May and mid-September, and it has two or three generations per year. Leafminer overwinters as pupae in the soil beneath a birch tree. In spring, the emerging adults mate and the females fly to birch leaves to lay their eggs on new leaves. The eggs get hatched in 4 to 14 days. The newly hatched larvae feed within the leaf for 8 to 12 days before emerging from the leaf as mature larvae. Mature larvae then drop to the ground, where they pupate and remain in the soil until maturing onto the adult fly which usually takes 2 to 3 weeks and then they are ready to start the cycle again.

Leafminers cause damage by tunneling or mining between the surface of the leaf with a small brown or reddish-brown, irregular-shaped patch on the upper surface of the leaf. If the mine is occupied, the larvae can be seen when the leaf is held up to a light. Those injected leaves will often appear curled at the edges. The leafminer attacks before the leaves have fully expanded, thereby interfering normal development and deformed leaf. The damage can cause stress and weaken the tree, making it more susceptible to serious problems such as bronze birch borer.

The easiest way to control this pest is to keep your trees healthy by supplying enough water and nutrients. Birch tree needs more water than most other trees. Spraying chemicals for the big trees is not environmental friendly as chemicals will be spread to the surrounding environment. Since the larvae are protected inside the leaf, use of chemicals spray is not effective control measure. A new system of injecting systemic insecticide directly into the trunk of the tree has been developed and has shown promising results in controlling this insect. The best way to get rid of this problem is to call trained certified arborist and discuss the options of controlling this pest. It should be worthwhile to remember that injecting tree with the systemic insecticide at the wrong place and the wrong time will do more harm than injecting insecticide in correct way.