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City of Mississauga Parks and Forestry - Pest & Disease Management

2020 Gypsy Moth Management: Work Updates

All ground spraying and tree injection work for the City's 2020 Gypsy Moth Management Program is now complete. Forestry staff thank residents and park visitors for their support.

To learn more about where treatments took place, visit the Treatment Areas section below.

Gypsy Moth

Gypsy MothGypsy Moth (Lymantria dispar) is an insect pest native to Europe that has been introduced to North America. Gypsy Moth caterpillars eat leaves from trees during the spring and early summer (causing defoliation or loss of leaves in trees) which when in high populations can have long-term effects on the health of the City's urban forest.

About Gypsy Moths

What are Gypsy Moths?

The European Gypsy Moth is considered to be a major pest in North America. In its caterpillar or larval stage, the insect eats the leaves of trees making them more susceptible to disease and damage from other insects.

How much damage can Gypsy Moths cause to trees?

High levels of Gypsy Moth caterpillars can cause trees to experience a loss of leaves, which could lead to weakness and make them more susceptible to diseases or weather fluctuations. Healthy trees are able to grow back their leaves within the season. However, several years of defoliation weakens trees and can have negative impacts on their long-term health.

What kinds of trees are most affected by Gypsy Moth caterpillars?

Gypsy Moths prefer oak trees but will eat all kinds of hardwoods including elm, birch, poplar and willow trees. In some rare cases, when the number of Gypsy Moths is extremely high, the caterpillar will feed on evergreens such as pine and spruce. They do not appear to like sycamore, butternut, black walnut, dogwood or balsam fir.

What is the lifecycle of the Gypsy Moth?

The moths are short-lived and seen in mid-summer. Both sexes die after the female lays its eggs on the limbs and trunks of trees, on rocks, buildings or in other sheltered areas. Egg masses remain in place all winter and hatch the following spring from late April to mid-May. Once hatched, the caterpillars begin to feed for approximately seven weeks.

Does the Gypsy Moth have any predators?

Yes. Predators include other insects like wasps, flies, beetles, ants and spiders and animals such as chipmunks, squirrels and raccoons. When caterpillars first hatch, birds such as chickadees, blue jays, robins and nuthatches will prey on them. Gypsy Moth populations are also reduced by diseases caused by bacteria, fungi and viruses.

What is the City doing?

Integrated Pest Management

The City uses an Integrated Pest Management (IPM) approach to control and manage the Gypsy Moth population to keep our urban forest healthy. IPM combines biological, cultural, physical and chemical tools in a sustainable way to minimize risks to the environment, economy and human health.

Each year the particular combination of tools and strategies used in the City’s IPM change in response to the abundance and distribution of the Gypsy Moth population, new and emerging science, and the complex set of stressors that face the City’s trees and natural areas. Through the IPM program, the City is committed to adapting its actions to current conditions and providing the most effective control possible. Recognizing the extraordinary adaptability of insects, IPM does not attempt to eradicate a particular pest entirely. Rather, it’s aimed at keeping pest populations below a threshold level at which they can cause significant economic loss or environmental harm.

History of the City’s IPM Program

  • 2003: City begins monitoring for Gypsy Moths.
  • 2006: Aerial Spray
  • 2007: Aerial Spray
  • 2012: City adopts an IPM approach to managing Gypsy Moths. Monitoring program is formalized. Hanging of pheromone traps and burlapping of trees begin.
  • 2015: Tree injections are first included in IPM Program and continue in select years moving forward.
  • 2018: Aerial Spray
  • 2020: IPM includes egg mass scraping, ground sprays, tree injections and monitoring.

*Note: These milestones represent highlights during identified years, as well as planned management in 2020. Methods vary year to year based on management needs and recommendations.

IPM Methods

Egg Mass Surveys
The City has a rigorous monitoring program that employs consultants to survey Gypsy Moth egg masses during fall and winter months. Data from these surveys are used to estimate the Gypsy Moth population and defoliation levels in the following year. Control strategies are recommended each year based on the results of the surveys and the most up to date information on effective Gypsy Moth management.

Egg Mass Scraping
This method involves scraping Gypsy Moth egg masses off of infected trees that are within reach into a container and then soaking them for at least 48 hours in soapy water to kill the eggs. As each egg mass contains 500-1000 eggs, this is an effective method to reduce caterpillar populations.

This method involves placing a ring of burlap around a tree at chest height. The burlap is secured to the tree with a string at its centre and then folded over to make two layers. Gypsy Moth caterpillars will seek refuge under the burlap layers in the heat of the day and can be removed and eliminated. Caterpillars also occasionally pupate in the burlap.

Pheromone Traps
Pheromone traps can be hung in trees in areas to attract male Gypsy Moths searching for females. Male moths that get stuck in traps and are then prevented from mating.

Tree Injections
Tree injections involve the use of TreeAzin® a botanical injectable insecticide formulated with azadirachtin, an extract of neem tree seeds (not neem oil), and is registered in Canada for use against Gypsy Moths, tent caterpillars and other tree pests. TreeAzin® is injected in a controlled way into the sapwood of a tree. This protects treated trees from Gypsy Moth defoliation during the year it is injected.

Ground Sprays
Ground sprays involve the use of products containing the active ingredient Bacillus thuringiensis subspecies kurstaki (Btk). Heavily infected trees can be sprayed from the ground by licenced operators using a controlled mechanism such as a pressurized hand-held hydraulic sprayer.

Btk is naturally occurring bacteria found in the soil that produces a protein that is toxic only to the larvae (caterpillars) of specific insect species. When ingested by susceptible insects, the toxic protein molecules destroy the walls of the insect’s stomach. The insect usually then dies within two to five days.

Btk is an effective pesticide that has been has been used globally for more than 30 years to successfully manage Gypsy Moth caterpillar populations.

Aerial Sprays
Aerial sprays are conducted in response to large scale, widespread increases in Gypsy Moth populations, when there is concern that increases in Gypsy Moth in addition to other stressors are a high risk to the tree canopy and no other IPM measures are able to keep populations within manageable thresholds.

In response to the large increase in Gypsy Moth and Fall Cankerworm populations, the City conducted aerial spray treatments in 2006, 2007 and 2018 using Foray 48B Biological Insecticide Aqueous Suspension, containing the active ingredient Bacillus thuringiensis subspecies kurstaki strain ABTS-351 (PCP# 24977) under the Pest Control Products Act (Canada). The goal of these spray programs was to lower both the Gypsy Moth and Fall Cankerworm populations.

2020 Gypsy Moth Management Program

Monitoring data from 2018 and 2019 indicate that the 2018 aerial spray program was effective in reducing Gypsy Moth populations in treated areas of the City. These areas are now considered to be low risk for defoliation in 2020.

In lieu of holding public open houses this year, Forestry staff have prepared the following video to inform residents about this year’s Gypsy Moth Management Program and what actions residents can take on their private property to reduce the population of Gypsy Moth in Mississauga.

Treatment Areas

This year’s management will focus on areas in Mississauga that are considered higher risk for defoliation. A variety of management strategies will be implemented for trees in certain City parks and along certain streets including tree injections, ground sprays, egg mass scraping, burlapping and pheromone traps. Not all methods will be conducted in each treatment area.

Portions of Wards 3, 4, 5, 7, 8 and 9 have been identified to receive treatment in 2020 and are depicted on the following maps. Street trees in these areas will be treated with injections only. Park trees will be treated with a combination of injections (Mississauga Valley Park, Paul Coffey Park and Sugar Maple Woods) and ground sprays (Applewood Hills Park, Garnetwood Park and Huron Park).

  • Ward 3 (including Applewood Hills Park and Garnetwood Park)
  • Ward 4 (Mississauga Valley Park)
  • Ward 5 (Paul Coffey Park)
  • Ward 7 (including Huron Park)
  • Ward 8
  • Ward 9 (Sugar Maple Woods).

Note that not all trees on the indicated streets will be treated, nor will all trees in indicated parks. Only trees that have been identified to be at high risk of defoliation in 2020 will receive treatment.

Treatment timing is dependent on a number of ecological factors (e.g.: leaf size, caterpillar size, and weather) but is anticipated to occur during the month of May.

Where can I find updates on when work is taking place?

Updates on timing will be posted frequently to this page during the month of May. Residents are encouraged to sign up for news alerts by joining our Tree Pest Management mailing list, by following us on social media (Facebook, Twitter and Instagram).

Frequently Asked Questions

We have prepared an FAQ document to answer some common questions that residents may have.

What can residents do?

The City needs the help of residents to control the Gypsy Moth population in Mississauga. If residents, especially those in neighbourhoods with a high number of oak trees, use IPM techniques on their own property, working together, we can keep Gypsy Moth numbers at a manageable level.

Here are some recommended IPM techniques that you can use on your property:

  • May to July: Pick caterpillars off leaves, tree trunks and branches and soak them in soapy water to destroy them.
  • May to September, Burlapping PDF Document: Install burlap wraps around tree trunks and then collect and destroy caterpillars and pupae.
  • June to August, Pheromone Traps PDF Document: Use pheromone traps to catch and confuse male Moths.
  • August to May, Gypsy Moth Egg Mass Search PDF Document: Scrape off and destroy egg masses.

Contact an Arborist if you have concerns about trees on your property.

Please call your local nursery or garden supply store for availability of the materials listed above.

Stay Connected

Sign up to receive news alerts on Tree Pest Management from the City’s Forestry team.

For more information on Gypsy Moths, email or call 3-1-1 (or 905-615-4311 from outside Mississauga).


The City has made a series of videos to help demonstrate some of the IPM techniques mentioned above.

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