Gypsy Moth and Cankerworm

Aerial spray program

Update -  aerial spray complete

The second and final aerial spray to control gypsy moth and cankerworm was completed successfully on the morning of Friday, June 1, 2018.

The first aerial spray was completed successfully on Friday, May 25. Some smaller areas were sprayed from the ground by bucket truck.


In spring 2018, the town conducted an aerial spray in select town woodlands with a safe and naturally occurring insecticide to control gypsy moth and cankerworm infestation. Review the map of the aerial spray program.

Please review our Frequently Asked Questions section for more information. If you have additional questions or concerns regarding the aerial spray program, please contact ServiceOakville at 905-845-6601.

What are they?

Gypsy moth is a non-native insect that is considered a major destructive pest in North America. Cankerworm (also known as inch worm) is a native insect that undergoes population increases every 10-15 years. When populations are high, they can eat all the leaves on a tree in a short amount of time. Successive years where leaves are lost can cause trees to die.

Based on population surveys conducted in 2017, Oakville faced extreme levels of gypsy moth and cankerworm infestation in 2018 that could have affected 110 hectares (272 acres) of town woodlands and result in a significant loss of trees if no action was taken.

The damaging effects of gypsy moth and cankerworm can be controlled with an effective Integrated Pest Management (IPM) plan.

The town will be conducting an aerial spray application of a safe and natural biological treatment called Bacillus thuringiensis Kurstaki (BtK) in town woodlands in mid-May 2018, weather permitting, to control gypsy moth and cankerworm infestation on town trees. Btk has been identified as the most effective method to prevent excessive defoliation from gypsy moth and cankerworm in heavily infested woodland areas. Some additional sites may be ground sprayed or have alternate control methods implemented.

Spraying will be performed by a low flying helicopter over the designated woodlands between 5 and 8 a.m. Two treatments will be necessary within approximately one week of each other. The most effective time to apply Btk is late April to mid-May when the gypsy moth caterpillars have recently emerged. The most up-to-date information on spray times, dates and maps will be posted on this page. Please check back here for details.

  • Learn more about the aerial spray program in our Frequently Asked Questions section
  • Review the staff report

About Btk

Public health and the safety of our environment are top priorities at the Town of Oakville. The aerial spray will use Foray 48B Biological Insecticide Aqueous Suspension, containing active ingredient Bacillus thuringiensis, subsp. Kurstaki (Btk) strain ABTS-351, (PCP# 24977) under the Pest Control Products Act (Canada).

The use of Btk is approved by Health Canada. Over the years of use worldwide, no public health concerns have been identified from exposure to Btk.

Btk is a soil bacteria that occurs naturally. The bacteria is poisonous only to a group of insects during the larvae stage of their life cycle. Btk does not affect adult moths or butterflies or other beneficial insects, honeybees, pets, birds, fish, or mammals. There is no impact on animals that may eat a gypsy moth caterpillar that has ingested Btk. Find out more about Btk on the Health Canada Btk Fact Sheet (pdf).

No special precautions are required for residents near the aerial spray areas. You may wish to alter your early morning plans such as running or dog walking as some woodlands will be closed briefly. You may wish to remain indoors and close windows to avoid any noise distraction from the helicopters.

Here’s what you can do to protect your trees and help control the spread:

  • Physically remove gypsy moth egg masses. Use a putty knife or trowel to scrap eggs into a container and destroy the eggs by leaving them in soapy water for several days.
  • Apply sticky bands or burlap around trees to trap emerging cankerworm and gypsy moth caterpillars. Commercial sticky bands can be found at most home and garden stores.
  • Use gloves to hand-pick caterpillars and crush.
  • Contact a professional tree care service provider to discuss Btk spraying.

For detailed control tips, review the Health Canada Gypsy Moth Pest Control page.

Forestry staff has been monitoring the population of gypsy moth since 2002. In 2005, staff observed an increase in Gypsy Moth population, and undertook a more comprehensive monitoring program.

As a result of a population increase in 2007, Oakville participated in a collaborative spray program in 2008 with neighbouring municipalities to spray 63 hectares (155 acres) of municipally infested woodlands with Btk. The aerial spray program was considered a success. The gypsy moth population in the following years was negligible and an integrated pest management approach that did not require aerial spraying was implemented. Forestry staff manually removed egg masses from the trees, where possible, prior to spring emergence.

Since the last outbreak of this pest in 2008, the overall risk to town’s municipal woodlands has been low. The 2012 and 2013 egg mass surveys conducted by the town’s consultant reported a slight increase in the population levels from those seen in previous years. High infestation levels were localized and protective injection treatments were implemented in select hot-spot locations from 2013-2017.

In the spring of 2017, the town’s forestry consultant recorded significant increase in the density and population of gypsy moth and cankerworm in town woodlands. In November 2017, Town Council approved the 2018 Gypsy Moth and Cankerworm Mitigation Plan.

What is gypsy moth?

Gypsy moth (Lymantria dispar dispar) is an exotic forest insect pest that is native to Europe and considered to be a serious defoliator of trees and shrubs. After severe or repeated defoliation (loss of leaves), trees can die or become so weakened that they are vulnerable to secondary infestations. All species of oak are susceptible to gypsy moth. This is of particular concern as oaks are high value heritage trees of immense significance to Oakville’s landscape and neighbourhoods.

What is cankerworm?

Cankerworm has two species: spring cankerworm (Paleacrita vernata) and fall cankerworm (Alsophila pometaria). Adult spring cankerworms emerge and deposit eggs in late March and throughout April, whereas fall cankerworm adults emerge and deposit eggs from late September throughout October. The larvae of both species emerge in the spring just as the leaves begin to appear and will feed on the foliage until mid-June. When feeding is complete, the larvae enter the soil where they remain until they emerge as adults.

How much damage can gypsy moth and cankerworm cause to trees?

According to the town's 2016 iTree Report, gypsy moth, if left untreated, has the potential to impact 409,000 trees in the town of Oakville. This is equal to 23 per cent of the town’s tree canopy. While the moth stage of the gypsy moth does not feed on trees, the caterpillar stage of this insect can potentially devour every leaf of the tree’s canopy. Both gypsy moth and cankerworm are capable of causing a considerable amount of damage to trees during an extreme infestation. The severity of the tree damage depends on the degree of infestation, past defoliations and the current health of the tree. If a tree has been weakened by previous defoliations or stressed by other conditions such as drought and attacks from other insects the defoliation can lead to the death of the tree.

What types of trees are most affected by gypsy moth?

All species of oak are susceptible to gypsy moth. The larva of this insect also feed on poplar, birch, willow, maple, beech, and cherry and if faced with a shortage of deciduous leaves, they will feed on conifers (hemlock and pine) and ornamental shrubs.

What types of trees are most affected by cankerworm?

The preferred trees of the cankerworm are maple and elm, but it also attacks ash, basswood, bur oak, white birch, and various fruit trees.

Do gypsy moth and cankerworm have any natural enemies?

Yes. At normal population levels, gypsy moth and cankerworm play a crucial role as a food supply for many of the native species of birds that live in Oakville’s urban forest, as well as other woodland animals such as raccoons. Usually, diseases caused by bacteria, fungi or viruses contribute the most to keeping gypsy moth and cankerworm levels low.

How severe is the gypsy moth and cankerworm infestation in Oakville?

In 2018, Oakville faces extreme gypsy moth and cankerworm infestation in a number of areas throughout the town. The infestations in these areas will result in the weakening or wide-spread loss of trees.

What is being done?

The Town of Oakville is conducting an aerial spray program in heavily infested woodlands. Based on research and results of previous aerial spray programs, aerial spraying of the biological treatment Bacillus thuringiensis Kurstaki (Btk) has been identified as the most effective method to deal with gypsy moth and cankerworm in heavily infested areas. Btk will be sprayed by low-flying helicopter over the target areas.

Is it safe?

Yes. Municipalities across Canada have conducted aerial spray programs in urban settings for decades. According to Health Canada, Btk poses no threat to human health through either handling products directly or being exposed to them indirectly during a spray program.

Aerial spraying:

The aerial spray will be conducted by Zimmer Air Services. Zimmer Air Services is highly experienced in the control of forest pests in municipal settings and has been approved for hire by the Ontario Ministry of Natural Resources and Forestry. The operation of low-flying helicopters for aerial spray application is approved by Transport Canada. Learn more about Zimmer Air Services.

Some roads near the woodlands will be closed briefly or experience short delays while the spraying takes place so that the low-flying helicopter does not distract drivers. There may be some brief minor noise disturbance as the helicopter passes over residential areas near the woodlands being sprayed.


The use of Btk is approved by the Health Canada Pest Management Regulatory Agency and is permitted under Oakville's pesticide-bylaw. It has replaced chemical insecticides in aerial spraying programs worldwide.

Research shows that Btk used in aerial spray programs has no negative environmental or human health effects. Btk is a bacteria which occurs naturally in soil. The bacteria is poisonous only to a certain group of insects when ingested during their larvae or caterpillar stage. For Btk toxins to be activated, alkaline conditions that exist only in certain insects' digestive systems must be present. The acidic stomachs of humans and animals do not activate Btk toxins. Btk does not affect adult moths or butterflies or other beneficial insects such as honeybees, or pets, birds, fish, or mammals. The aerial spray will not affect Monarch butterflies as they are not in the caterpillar stage at this time of year.

Btk biodegrades quickly and there are no groundwater contamination concerns.

The aerial spray is conducted only under ideal weather conditions which includes very little wind. The public is unlikely to see or feel the spray or experience any affects. No special precautions are necessary or required.

Learn more about Btk on Health Canada's Btk Fact Sheet (pdf) and on Natural Resources Canada's website.

If you have questions or concerns related to the health impacts of aerial spraying with Btk, please call the Region of Halton Public Health Department at 905-825-6000.

When will the spraying take place?

Spraying will occur on two separate days from 5-8 a.m., sometime between April 30 and June 15, 2018, most likely in mid-May once the gypsy moth caterpillars and cankerworms have emerged. The aerial spray program must take place when the gypsy moth and cankerworm larvae are just emerging in order to be effective. Spraying is dependent on weather and will only be done in the right conditions. As a result, specific spray dates are chosen between 12 and 48 hours in advance, and can be cancelled if weather conditions change. Residents within the affected spray areas are encouraged to check for updates on the News and Notices page and the town’s Facebook and Twitter accounts.

What areas of Oakville will be sprayed?

The aerial spraying will be conducted over select town woodlands only. Spraying will not take place over town streets or residential properties. There are 21 woodlands in the 2018 aerial spray program. Some sites may be ground sprayed or have alternate control methods implemented. Woodlands and trails will be closed briefly while the spraying takes place and reopen immediately after. There are no health concerns with entering the woodland after the trees have been sprayed. Review the aerial spray program map.

What roads will be affected?

Traffic may be delayed briefly on residential roads near the woodlands as the helicopter passes overhead so the helicopter does not cause a distraction to drivers. There may be short delays on Oakville Transit routes 11, 14 and 33 during this time.

The following roads will be closed to traffic very briefly (five to fifteen minutes) between 5 and 6 a.m. on both days of the spray operation as the helicopter passes to adjacent woodlands:

  • Upper Middle Road between Grand Boulevard and Joshua Creek Drive
  • Upper Middle Road between Trafalgar Road and Eighth Line
  • Neyagawa Boulevard between Upper Middle Road and River Oaks Boulevard

The following closure on Ford Drive will take place very briefly between 6 and 6:30 a.m. on both days of the spray operation:

  • Ford Drive between Aspen Forest and Devon Road

Will the town spray my trees?

The town's Urban Forestry section is responsible for the maintenance of town trees only.

What can I do to protect my trees?

There are many ways private tree owners can protect their trees from gypsy moth and cankerworm. Contact a certified tree service provider for information on treatment options or review the What You Can Do section on this page or Health Canada's Gypsy Moth Fact Sheet (pdf).

What is the town doing about other insect pests?

Most insects are a nuisance only and under normal circumstances do not require a control program. Visit the town's Invasive Species page to learn more.