Birch Leafminers

What Is It?
Three species of sawflies (Fenusa pusilla, Profenusa thomsoni, Heterarthrus nemoratus) introduced from Europe in the early 1970s can be responsible for the premature browning of birch trees.
The lathrolestes luteolator; a small wasp that hunts birch leafminers
What's the problem?
The larvae feed on the inner green tissues of the leaf, causing a discoloured spot. Feeding over several weeks causes the blemish to take on a blister-like appearance.

A single leaf can contain many larvae whose blisters may merge to destroy much of the leaf. Heavy attacks repeated over several years will cause stress, making the tree more susceptible to other problems.

What Can I Do?

To support the biological control of birch leafminers, we do not recommend chemical birch leafminer treatments. Since 1990, populations of a tiny wasp (Lathrolestes luteolator) which selectively attacks the most damaging birch leafmining pest (Profenusa thomsoni) have developed and drastically reduced the problem.

The following tips will help you maintain a healthy birch tree will be more resistant to any birch leafminer attack:
  • Roots of birch trees need a cool, moist, shady location. Proper site selection is crucial for a long, healthy existence.
  • Fertilizing is best done in early spring at the onset of the growing season. Lawn fertilizer applications around the tree may be sufficient.
  • Prune any dead wood and remove the smaller of any branches that rub 1 another. Birch tree pruning is best done after the leaves are fully developed (June to July).
  • During the growing season, provide water during prolonged drought conditions. Thoroughly soak the area under and around the tree at least once a week if there is little rainfall.
  • To reduce the risk of mechanical damage from lawn mowers, weed eaters etc. , do not have any sod immediately surrounding the tree trunk.