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Cankerworms

Note: The City also has a specific invertebrate pest control program to manage cankerworm populations in Regina.

Characteristics

  • Larvae The eggs of both the fall and the spring cankerworm species hatch in spring and turn into larvae. Cankerworm larvae are light green to brownish-green, often with a darker stripe down the back. They are sometimes called inch worms or loopers. Cankerworm larvae spin "silken threads" that allow them to:
    • escape predators
    • be blown by the wind to other trees
    • drop to the ground and burrow into the soil when full grown
  • Adult Adult male cankerworms turn into silver moths which appear either from mid-September to October (for fall cankerworms) or from the end of March to mid-May (for spring cankerworms). After emerging, the wingless female moths crawl up trunk of American and Siberian Elms, Manitoba Maple trees or fruit trees to lay their egg masses in the tree’s crown.

Identifying infestations

  • “Shot holes” in new leaves As they feed, larvae will create small ‘"shot holes" in new leaves. The cankerworm will also be found under the leaf.
  • Leafless trees Large populations of cankerworms can eat all the leaves off trees and shrubs. Healthy trees usually produce new leaves by mid-July. However after several years of heavy infestations, the tree’s crown may die back.

IPM Toolkit

  • Preventive tools
    • Not applicable
  • Physical tools Band ALL your elm, fruit, or Manitoba Maple trees in the spring (late March to mid-May) and fall (September to mid-November) to trap female cankerworms as they crawl up the trunk to lay their eggs. You can hire a company to do the work or band the trees yourself:
  1. Purchase fibreglass insulation (15 – 20 cm ide), plastic (black garbage bags also work), sticky substance (axle grease, Tanglefoot, Stick-em) and duct tape
  2. Wrap a strip of fibreglass insulation around the trunk about 1 to 2 metres above the ground.
  3. Cover the insulation with plastic and secure with duct tape.
  4. Cover the plastic with your sticking agent.
  5. Regularly re-apply your sticking agent and remove debris to ensure effectiveness.
  6. Remove your band after mid-May and again in mid-November to keep your tree bark in good shape. (Save the insulation for the next banding season.)
  • Biological tools
    • Not applicable
  • Chemical tools
    • Biological pesticides containing the bacteria Bacillus thuringiensis kurstaki (Bt.k.) can control cankerworm infestations. Follow label directions for proper application to specific branches where cankerworms are present.
    • You can apply Bt.k. on your own private trees; however, you need to hire a certified, commercial tree sprayer to apply Bt.k. on City-owned trees in your yard.
    • It is illegal for homeowners and private contractors to spray any other products on City-owned trees.