birch tree with blue sky in edmonton

Leaf Miners in Alberta: Symptoms and Treatments

Leaf miners are harmful pests that target urban forests throughout Alberta. Also called sawflies, leaf miners are native to Europe. However, they made their way to Canadian forests between 1920 and 1960.

They’re one of the most common insects that affect birch trees in North America. Here’s what you need to know about these nasty pests.


How to identify leaf miners

Leaf miners are winged insects and are closely related to bees and wasps. Adult leaf miners are between three and six millimetres long, black and resemble house flies. There are five different species of leaf miners found in Alberta.

You can find evidence of leaf miners in damaged birch tree leaves. Leaf miner larvae feed on the green tissue of birch tree leaves, turning them brown. Consequently, if it looks like the tree has suddenly dried up or become infected with a disease, it’s probably infested with leaf miners.


Leaf miner life cycle

Leaf miners spend winters as prepupae in the soil and emerge as insects in May. Adult females begin laying eggs inside birch leaves in June. The females cut tiny slits in the birch leaves to deposit their eggs. When the eggs hatch, worm-like larvae start munching away at the green tissue inside the leaves, creating “leaf mines.”

After feeding for several weeks, the larvae drop to the ground, burrow themselves into the soil and form cocoons where they spend the winter.


How to treat leaf miners

Outbreaks of leaf miners in Alberta have been successfully controlled by a native parasitic wasp. The wasps lay eggs inside the leaf miner larvae. When the eggs hatch, the parasitic wasps consume and kill the leaf miners. The wasps are now used as a biological control agent and have kept leaf miner numbers low in Edmonton since the 1990s.

For this reason, you shouldn’t use insecticide on your birch trees to eradicate leaf miners as the poison will also kill the beneficial wasps.


Can my Birch tree be saved?

Fortunately, leaf miners don’t kill birch trees. However, the damage they inflict on the leaves robs the trees of their ability to photosynthesize nutrients. This damage stresses and weakens the trees, making them more vulnerable to other harmful pests and diseases.

Keeping your trees healthy as possible is the best way to minimize leaf miner damage. Water your trees during prolonged periods of drought, fertilize them in the spring and prune dead branches after the leaves are fully developed in June or July. Additionally, keep sod and grass away from your trees to avoid damage from lawnmowers and trimmers.


All Season Tree Service in Alberta

At All Season Tree Service, our team of professionals know all about tree pests and diseases and what needs to be done to safely care for your trees. Contact us to schedule an appointment or to get a free quote to keep your trees happy and healthy all year round! We serve residents and property owners in Edmonton, Sherwood Park, Spruce Grove and all surrounding areas!