Control Canada Thistle – Gall Flies

Gall Flies Offer Biological Control of Canada Thistle


How they work

Female flies bore into the stem of the thistle to lay their eggs. The larvae hatch and eat the thistle from the inside, causing a gall to form. This gall is a stressor and a nutrient sink and hinders plant growth. This includes the flowering heads which lowers seed production.

Do they overwinter?

Yes, the larvae overwinter in the gall and emerge as adults in the spring.

Do they affect any other species of plant?

No, they are restricted to the target plant: Canada thistle.


$150 per tray (plus GST).  A tray contains 100 flies.

Ordering Details

Deadline to order is April 3, 2020.

Payment is due at time of ordering. Payment is accepted at the County of Barrhead, Westlock County, or Athabasca County Offices.

Delivery Details

Trays will be delivered in the early summer of 2020.


For more info please call Lisa at Highway 2 Conservation:  780-674-8069