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How to get rid of sawfly larvae on your trees

Sawfly larvae on a leaf

What is a sawfly?

Sawflies can wreak havoc on urban trees in Western Canada. The sawfly larvae feed on spruce needles and leaves, severely defoliating trees and making them weak and susceptible to disease. Left unchecked, a sawfly infestation can kill a tree in three years. That’s why it’s essential to identify, treat and control sawfly larvae colonies on your trees.

Types of sawflies

There are about 600 species of sawfly in Canada. They live everywhere, especially in boreal forest regions. Their name is derived from a saw-like appendage females use to cut open the soft tissue of plants and lay their eggs. The most plant destructive species in Western Canada include:

  • Yellow-headed spruce sawfly larvae feed on the needles of white, black and blue spruce trees. Larvae eat the needles one at a time, leaving entire branches brown and defoliated, restricting the tree’s ability to photosynthesize energy. This is the most destructive sawfly in urban forests.
  • Large rose sawfly larvae feed exclusively on wild and domesticated rose bushes.
  • Elm zigzag sawfly is a species that has only recently been identified in Canada. The larvae feed the leaves of elm trees and can cause extreme defoliation.

What does a sawfly look like?

Early sawfly identification is vital to keeping populations under control. Adult flies resemble wasps but without the space between their abdominal segments.

The larvae of the yellow-headed spruce sawfly have brownish-orange heads and green bodies marked with six grey stripes. They can grow to a length of about 20 centimetres. Larvae are fully developed by early to mid-July.

Sawfly larvae treatment and prevention

Inspect your trees in late spring and early summer to keep sawfly populations under control. If you spot larvae on your trees, you can remove them by hand or spray them off the tree using a strong jet of water.

For more advanced infestations, you may need to apply a pesticide. Try back-to-back applications of Trounce, two weeks apart. Trounce is an organic pesticide that controls a broad range of insects. It’s a natural solution that breaks down and has no residual effects. Using a professional arborist will ensure the application is done correctly and reduce the risk of killing other beneficial insects such as bees.

Sawfly larvae control in Calgary and Edmonton

At ArborCare®, we can help control your sawfly problem and any other pests that may be invading your yard. With our plant management program, arborists maintain and care for your trees and can treat infestations before they become a severe threat. Contact us today to learn more about our program.

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