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Update on Gypsy Moths August 20, 2020

Dear MPOA members,

We have already witnessed a significant regrowth on the many deciduous trees that were stripped of leaves by the gypsy moth caterpillars in June and aside from some residual damage to pines thing appear to be returning towards normal. What can we do to prevent this from happening again next year? Now is the time to destroy the egg masses that are generally found  in small oval shaped light brown clumps on the lower 10 feet of tree trunks. This can be accomplished by scraping them into a pail and either burning them or soaking for 48 hours in soapy water. An alternative is to spray the egg masses with horticultural oil (purchased from a garden centre). Once the egg masses are saturated with oil the eggs inside will suffocate. Remember it is not adequate to just scrape the eggs onto the ground since they will still hatch. The final option is to get a commercial organization like Zimmer Air ( to spray your property. They spray a bacteria (known as BT) in late May or early June which kills the caterpillars after it is ingested. Usually this requires neighbours to be in agreement (a signed waiver is required from each) and  the expense (up to $400 per lot) would be shared by all lots that are sprayed. The Ministry of Natural Resources tells me that they are monitoring the situation but that they have no plans to spray crown land. The accept no responsibility for pest control on private property. See their reply to me (appended):       ……………………….. Bob Reid MPOA president


From: NRISC (MNRF) <>
Sent: August 14, 2020 2:34 PM
To: Robert Reid <>
Subject: RE: Reply: Yes, Page:


Thank you for sharing your concerns about the defoliation which is occurring due to gypsy moths and its impacts on our forests. We would like to provide you with the following information.

Gypsy moth outbreaks are cyclical, typically occurring every seven to 10 years. In Ontario, major outbreaks have occurred in 1985, 1991 and 2002. The most recent outbreak, which peaked in 2008, was much less severe than previous ones. This is because the impacts from gypsy moth are gradually becoming less severe as natural parasites and diseases have adapted to regulate populations.

Gypsy moth are a free-feeding defoliator of hardwood tree species that feed from late May to late June. Once the feeding ceases, severely defoliated trees have the ability to produce a second crop of leaves that will enable them to continue to grow throughout the summer. During severe outbreaks, trees and shrubs are completely defoliated over large areas. Despite the trees’ ability to produce a new crop of leaves over the summer, the damage causes significant growth loss. Understory shrubs and plants may also be affected. Trees growing vigorously can withstand a few seasons of severe defoliation with little impact.

The Ministry of Natural Resources and Forestry conducts field and aerial surveys annually to monitor and assess forest health across the province, and may take action, such as spraying with BTK (Bacillus thuringiensis), to protect crown land forests, when appropriate.

The Province of Ontario does not carry out insect control programs on private land. Pest management on private land is the responsibility of the landowner or municipality. Landowners wishing to reduce impacts on their property have the option to have trees sprayed with BTK in the spring by a registered pesticide application company. This approach may be best carried out by coordinating efforts with other landowners wishing to spray.

On a smaller scale (ornamental or yard trees), there are several approaches available to help control gypsy moth, including physical removal of egg masses in the fall/winter, or removing and burning egg masses or soaking them with soap and water mixture. Also, in the spring, once the eggs have hatched, a band of either burlap or other cloth product wrapped around the trunk will provide a place for caterpillars to hide during the heat of the day. Check these bands regularly and scrape caterpillars into a container of soapy water. Healthy trees are better able to ward off attacks and withstand stresses such as defoliation.

To support landowners in the management of gypsy moths, the ministry and its partners have developed fact sheets that provide information and outline best management practices. Please visit and for more information. The Ministry of Natural Resources and Forestry also continues to monitor the location and impacts of gypsy moth to Ontario’s forests.


If you have any further questions, please contact Dan Rowlinson, Forest Health Monitoring Program Coordinator, MNRF Science and Research at (705) 946-7445 or

Thank you again for your message.



NRISC web reader – LS


Ministry of Natural Resources and Forestry

Natural Resources Information and Support Centre

300 Water Street, 5th Floor N

Peterborough, ON K9J 3C7


TTY: 1-866-686-6072