Gypsy moth and cankerworm control

Help control the spread! Join us for a Gypsy Moth and Cankerworm Information Session to learn what the town is doing and what you can do to protect our urban forest from the damaging effect of these insects.

Tuesday, April 10, 6-7:30 p.m.
Queen Elizabeth Park Community and Cultural Centre
2302 Bridge Road, Multi-Purpose Room

What are they?

Gypsy moth is a non-native insect that is considered a major destructive pest in North America. Gypsy moths can be a concern because the larvae (caterpillar stage) feed voraciously, mostly on the leaves of deciduous or leafy trees such as oak. If the caterpillar population is high, they can defoliate whole trees and entire woodlands in a short amount of time. While trees can often survive one season of defoliation, successive years where leaves are lost can cause trees to die, particularly when coupled with other forest pests like cankerworm.

Cankerworm (also known as inch worm) is a native insect that undergoes cyclical population increases every 10-15 years. Cankerworm has a significant impact on tree health in peak population years.

Based on population surveys in 2017, Oakville faces extreme levels of gypsy moth and cankerworm infestation in 2018 that could significantly affect 110 hectares of town woodlands and our overall urban forest.

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 the spring of 2018 to control gypsy moth and cankerworm infestation on town trees. Btk has been identified as the most effective way to prevent excessive defoliation from gypsy moth and cankerworm in heavily infested woodland areas. Some sites may be ground sprayed or have alternate control methods implemented.

Spraying will be performed by a low flying helicopter over the designated woodlands and typically done early in the morning, between 5 and 8 a.m. Two treatments will be necessary within five to ten days 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 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).

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 around trees to trap emerging spring 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.
  • Use burlap banding to catch gypsy moth caterpillars.
  • Contact a professional tree care service provider to discuss Btk spraying. You can find a list of certified arborists at the ISA Ontario website. Visit our Arborist Licensing page to learn more.

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, 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 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, particularly during a severe 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.

Does the gypsy moth have any natural enemies?

Yes. Natural enemies of the gypsy moth include other insects such as wasps, flies, beetles, ants and spiders as well as birds, chipmunks, squirrels and raccoons. Usually, diseases caused by bacteria, fungi or viruses contribute the most to keeping gypsy moth 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 way 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 for decades.

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. Learn more about Zimmer Air Services.

The operation of low-flying helicopters for aerial spray application is approved by Transport Canada. Some roads near the woodlands will be closed very briefly while the spraying takes place so that drivers are not distracted by the low-flying helicopters.

Btk: The use of Btk is permitted under Oakville’s pesticide-bylaw. Btk is a naturally occuring pesticide approved by the federal Pest Management Regulatory Agency.

According to Health Canada, Btk poses little-to-no threat to human health through either handling products directly or being exposed to them indirectly during a spray program. Some people with respiratory problems may experience mild irritation if directly exposed to Btk. If you experience any issues, please contact your doctor and report your incident to Health Canada.

Btk is a bacterium that occurs naturally on dead or decaying matter in the soil. It is grown from soil bacteria that occur naturally worldwide. When a caterpillar ingests Btk, a protein called endotoxin is triggered that poisons the insect’s digestive system. The caterpillars must ingest the Btk in order for the pesticide to be effective.

According to Health Canada, Btk is only toxic in the caterpillar stage of the gypsy moth life cycle. 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. It does not affect adult moths and butterflies, specifically Monarch butterflies, as they are not in the caterpillar stage at this time of year. Other insects including honeybees, as well as fish, birds or pets, are not affected by Btk. Btk biodegrades quickly and there are no groundwater contamination concerns.

Learn more about Btk on Health Canada’s Btk Fact Sheet (pdf) and on the Halton Region’s website.

When will the spraying take place?

The aerial spray program must take place when the gypsy moth is at a specific stage of development in order to be effective. The spraying will most likely occur in early to mid-May. The spray dates are highly dependent on weather conditions. The most up-to-date information on the spray times and dates will be posted on the town’s website.

What areas of Oakville will be sprayed?

The aerial spraying will be conducted over affected town woodlands only. Spraying will not take place over town streets or residential properties. There are 26 woodlands in the 2018 Gypsy Moth and Cankerworm mitigation 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. Maps will be posted on this page as details are confirmed.

Will the town spray my trees?

The town’s Urban Forestry section is responsible for the maintenance of town trees only. 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 Health Canada’s Gypsy Moth Fact Sheet (pdf).

Where can I find more information on insect pests?

Visit the town’s Invasive Species page.