Cankerworms & Tent Caterpillars

Every year cankerworms cause extensive damage to trees in Regina. They feed on most broad-leaved trees and shrubs, but prefer American and Siberian Elm, Manitoba Maple and fruit trees. The first signs of infestation are the appearance of small ‘shot holes’ in new leaves and larvae can be found under the leaves. During severe outbreaks, trees and shrubs may be completely defoliated. Healthy trees will usually produce a new crop of leaves by mid-July. After three or more consecutive years of heave attack, tree growth is slowed and branches in the crown may die back.

Cankerworm larvae are light green to brownish-green, often with a darker stripe down the back. They are sometimes called inch worms or loopers. Cankerworms spin ‘silken threads’ that allow them to drop from foliage to escape predators. The ‘silk thread’ also allows cankerworms to be blown by the wind to other trees.

Cankerworms drop to the ground and burrow into the soil when fully grown. Moths of the fall cankerworm emerge from their cocoons in mid-September and October. Spring cankerworms remain burrowed throughout the summer, fall and winter and emerge as moths from the end of March to mid-May. After the moths emerge they crawl up the trees to lay their egg masses in the crown of the tree. The eggs of both the fall and the spring cankerworm hatch in spring.

Cankerworms & Tent Caterpillar Control Program

There are three main components to the City's cankerworm control program.

Step 1 - Monitoring

More than 400 traps are placed on various trees throughout the city to monitor the populations of adult male and female cankerworm moths in each area. Cankerworm counts are done on the bands during the spring and fall emergence periods to determine which areas have the highest level of cankerworm concentration for a particular year and require spaying to control these populations. 

Step 2 - Spraying

City crews spray City-owned trees in areas with high concentrations of cankerworms. Areas identified as having higher population levels are sprayed first and as time allows we move to the next level of infestation, in decreasing order of trapped adult concentrations. Spraying is done from mid-May to mid-June when the worms are hatching and feeding on trees. A commercial product containing BTK is used. BTK affects only worms and is non-toxic to other insects, birds, animals and humans. The worms eat the product, stop feeding in 2-3 hours and die in a few days.

The City does not go out to an individual house to spray the trees or spray private trees. Those that have sensitivities can call the Pesticide Advisory Line for information on where and when the City is spraying. Residents are asked to move their cars off the streets while their areas are being sprayed. 

Step 3 - Public Awareness

Residents are encouraged to band private and City trees during the spring and fall emergence periods. Tree banding can reduce or manage populations and reduce the need for spraying. Banding trees controls cankerworm populations by trapping wingless female cankerworms as they crawl up the tree to lay their eggs. You should band your trees from late March to mid-May and again from early September to mid-November to catch the cankerworms moths at both the times they are emerging from the soil. It is important to band all trees in an area or else cankerworm larvae could move from unbanded trees to banded trees. Please do not leave bands up longer than recommended as it can do more harm than good to the tree.