Inch Worms, Cankerworm Outbreak


We live in the beach and have 5 large oak trees. They are approx 80 feet in height and 90 cm in diameter. This year we have had an infestation of inch worms and their poop. What can we do about them and will they damage our trees? I know they are eating holes in the leaves, but will they do further damage? Is there anything we can do to kill them and to prevent them from returning? I am concerned about the health of our very mature oaks! Thank you for your reply.




Thank you for contacting Toronto Master Gardeners.

Unfortunately this year is the outbreak year for inchworms (or cankerworm) here in Toronto, Mississauga and some other Canadian Cities.

According to the City of Toronto:

Usually, serious infestations break out every 8 or 12 years in forested areas. These infestations are historically less frequent in urban forests. The last similar outbreak in Toronto occurred in 2000.

Caterpillars feed on tree leaves from late April to mid-June. The damage is final for this year and the caterpillars are moving to pupate in the soil. At this stage of insect’s development, there is no effective control.

Healthy vigorous trees will put on new leaves later in the summer.

In the fall, Urban Forestry staff along with local community groups will monitor the affected areas to determine further action.

This spring, Urban Forestry implemented a successful control of gypsy moth outbreak. Fall cankerworm is often confused with gypsy moth because they appear at similar time and they cause defoliation of similar host plants.

For Specific Management Practices for Control of Fall Cankerworm, visit the website of the city of Toronto;

and for more information:

Good luck!