Tara Kearsey
Northern News Services

Yellowknife (Aug 14/00) - A foreign pest is preying on Northern birch trees.

Thousands of trees in Hay River and the capital city are infested with a species of the birch leaf miner, known as the sawfly.

These insects inflict damage to the leaves of birch trees. The first signs of an infestation are light green or grey spots, which eventually develop into brown blotches. As the insects feed between the surfaces of the leaves, the brown blotches increase in size and eventually cover most of the leaf.

The birch leaf miner is not native to the North, or even Canada. The insects were inadvertently transported from Europe to North America in the early part of the 20th century.

The pest has been in the North at least since the 1980s, but the last infestation of this magnitude has not been seen since 1998. The problem has also surfaced later than usual, as birch trees normally show signs of infestation earlier in the summer.

"Once you've got it, it can be an ongoing problem. (The infestation) is present and we're probably going to have it all the time," said Bob Decker, forest ecologist for RWED in Hay River.

"There are no natural predators of this particular pest and that's why we get these outbreak levels."

Decker said he was driving around Hay River late last week and noticed that a lot of birch trees were showing the signs of birch leaf miner damage.

Although the insect destroys most of the inner tissue of birch leaves, the tree itself does not usually experience serious damage.

"It's just a cosmetic thing: the leaves look unsightly," said Decker.

However, the insect attack does cause serious stress to birch trees. If the infected tree experiences repetitive attacks, does not receive enough moisture and is invaded by other insects, the branches of the tree could die.

But Decker said the infestation is a headache you just have to live with.

There are pesticides available, he said, but they have to be applied at a certain point in the insect's life cycle. Even then, pesticides pose a health hazard to both humans and household pets.

Birch leaf miners have attacked birch trees in Yellowknife as well. Mackenzie Management has applied the pesticide Cygon 2E to birch trees located near Range Lake Manors North and South, Hudson House, Franklin House, Frobisher House and Rockcliff and Rockridge Apartments.

Any contact with trees near these buildings should be avoided by all humans and pets until after Aug. 14. For more information on pesticides for birch leaf miners, call Agriculture Canada's Pesticides Directorate at 1-800-267-6315.

Yellowknife city officials have sent samples of birch tree leaves to Edmonton for analysis, to positively determine if the leaf discolouration is in fact the work of the birch leaf miner.