There are many different pests or diseases that can affect the health of our trees. Insects such as the Emerald Ash Borer (EAB), Cankerworm, Spongy Moth and Asian long-horned beetle, and diseases such as Oak Wilt can have devastating effects on the health of the urban forest.
Reducing the vulnerability of the city's urban forest to pests and diseases involves implementation of a wide range of urban forestry practices, including:
- Plant health care: site-appropriate tree species selection, young tree pruning, watering, and mulching;
- Improving tree habitat: increasing soil volumes, improving soil quality, reducing above and below ground completion for space and resources;
- Diversifying the urban forest: establishing underutilized and new native and non-invasive tree and shrub species;
- Improving knowledge and understanding of the urban forest: conducting a public tree inventory and improved species-based pest vulnerability analysis, increasing monitoring, species and stock suitability trials;
- Pest-specific management: development and implementation of targeted strategies to mitigate the effects of specific insects or pathogens.
Cankerworm
Cankerworms are native leaf-eating caterpillars, whose population peaks every 10-15 years and can cause widespread leaf damage. Damage in 2017 was significant, and the populations of these caterpillars are expected to peak for one to two years, then decline as natural predators such as birds along with caterpillar diseases reduce the populations naturally. Hardwood trees can survive one to two years of defoliation.
Trees impacted by cankerworms
The most common trees that this species prefers to feed on are ash, basswood, beech, black cherry, red maple, sugar maple, red oak, and white oak. It will also feed on the leaves of apple, birch, boxelder, dogwood, elm, hickory, and many other hardwoods.
Help reduce cankerworm populations
| How to create a tree sticky band |
| Creating a “Sticky Band” around your trees can help reduce cankerworm population and help keep our urban trees and forests healthy. |
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| Wrap the tree with polyester or cotton banding |
| Wrap a 10 to 15cm wide strip of polyester or cotton (quilt) batting around the trunk of the tree you are going to be banding - about five feet (1.5m) off the ground. Keep out of reach of pets and young children |
| Cover the wrap with plastic wrap or a garbage bag |
| Cover the polyester or cotton (quilt) batting with a sheet of plastic wrap or a garbage bag. Allow several inches of plastic above and below the insulation. For larger trees you may need to tape multiple bags together. |
| Tape the band covering to secure to tree |
| If you are using plastic bags or plastic wrap, tape the plastic to the tree with duct tape or packing tape. Please do not use nails or staples to attach the plastic to the tree as this will injure the tree. |
| Apply sticky substance to tree band |
| Spread a layer of a sticky substance, such as TanglefootTM (non-toxic, not a pesticide, available at garden centres and hardware stores) as directed or petroleum jelly, on the plastic. This will make the cankerworms stick to the band. Be sure to wear gloves as it is very sticky! |
| Inspect and maintain sticky band |
| Inspect the sticky material regularly and remove leaves, insects and other debris and reapply sticky material if required. |
| Remove sticky band at the end of the season |
| Bands should be removed by late spring and reapplied in the fall. It is important to remove the bands to prevent damage or discolouration of the bark. |
Cankerworm Frequently Asked Questions (FAQs)
Will cankerworm kill my trees? |
| Cankerworm will not kill healthy trees. Healthy vigorous trees will put out new leaves later in the summer. |
What is the lifecycle of cankerworm? |
| In spring the caterpillars feed on leaves from April to mid-June. Then they move into the ground for the next six months to mature into adult moths. The moths emerge from the soil in November - December and lay their eggs in the tree canopy. |
What kind of trees are affected by cankerworm? |
| Cankerworm is most commonly found on hardwood species such as oaks, maples, elms, and ash. |
What should I do if I have cankerworms on my tree? |
| Cankerworm damage can be controlled on your trees in an environmentally friendly way in the late fall season. A sticky band installed around the main stem of the host trees traps the female moths and prevents them from climbing up the tree to lay their eggs. Female cankerworm moths do not fly and must climb up the nearest tree to lay their eggs. If you are banding trees on your property, make sure you band all trees that are susceptible to the insect. Banding your trees should start in late-October and can be removed by late-December. |
Are there natural predators to cankerworms? |
| Yes, natural organisms such as parasitic wasps, birds, mice, ground beetles, and bacteria usually keep cankerworm population levels in check. However, serious infestations do break out from time to time, usually every eight or 12 years in forested areas. Mild winters, such as the one we recently experienced in 2016-2017, can also help lead to an increase in cankerworm populations. |
What can you do for your private trees? |
| Banding trees is a way to help trap and stop cankerworms from crawling up the tree to lay their eggs. Banding should ideally be done before frost. |
How do I band a tree? |
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For a video showing this process please see the City of Toronto instructional video available at: |
Emerald Ash Borer
The Emerald Ash Borer (EAB) is a non-native beetle that lives in ash trees and lays eggs on the bark and bark crevices. The larvae then tunnel beneath the bark and feed on the layer of live cells between the bark and the sapwood, cutting off nutrients and water to the upper portions of the tree.
Signs of Infected Emerald Ash Borer Trees |
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Signs of the EAB usually only become apparent once a tree is heavily infested. The following are signs and symptoms your ash tree may be infested with the EAB:
A certified arborist should inspect your tree to confirm the presence of the EAB and to recommend treatment options. |
Emerald Ash Borer in Burlington |
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The presence of the EAB in Burlington was first confirmed in 2010. The EAB has now been identified in pockets throughout the city. The city's population of ash trees, which make up about 13 per cent of the urban forest, is at risk due to EAB. Forestry staff are working towards removing infected trees and replanting them with trees that are more resilient to EAB and other potential diseases. |
Emerald Ash Borer Quarantine Regulations |
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To limit the spread of the EAB, the Canadian Food Inspection Agency prohibits moving any species of firewood and ash tree products (nursery stock, logs, lumber, packaging, wood, bark, wood chips or bark chips) from the Burlington and Region of Halton area to any other surrounding regions. For additional information on the EAB, you can visit the Ontario Ministry of Agriculture, Food and rural Affairs management strategy page or the Canadian Food Inspection Agency. |
Oak Wilt
Oak wilt is a vascular disease of oak trees, caused by the fungus Bretziella fagacearum that can damage and destroy an oak tree in a single growing season. The fungus grows on the outer sapwood of oak trees and damages the tree by restricting the flow of water and nutrients through the tree. All oak species are susceptible and at risk.
Oak wilt is a vascular disease of oak trees, caused by the fungus Bretziella fagacearum that can damage and destroy an oak tree in a single growing season. The fungus grows on the outer sapwood of oak trees and damages the tree by restricting the flow of water and nutrients through the tree. All oak species are susceptible and at risk.
Oak wilt has spread throughout the Eastern United States and has been present since the 1940s. In 2023, oak wilt was confirmed for the first time in Canada in Niagara Falls and the Township of Springwater. While oak wilt has not been identified in Burlington, the City encourages residents to become familiar with the signs and symptoms of oak wilt in order to minimize the threat to oak trees locally.
Trees impacted by oak wilt
All oak species are susceptible and at risk. The red oak group (red, black, pin) is the most susceptible, with mortality frequently occurring within one growing season. Oaks in the white oak group (white, bur) are also affected but are more resistant.
Oak Wilt Frequently Asked Questions (FAQs)
What are the Signs and symptoms of oak wilt? |
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Understanding the signs and symptoms of oak wilt can help residents identify oak wilt and report it to the City. Signs and symptoms include:
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How can I help prevent the spread of oak wilt in Burlington? |
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What do I do if I suspect oak wilt is on public or private oak trees? |
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The City is asking residents who have oak trees on their private property to inspect their trees for oak wilt. If residents suspect oak wilt to be present on their oak tree or on a City-owned oak tree, they are asked to call the customer contact centre at 905-335-7777 or email at city@burlington.ca. To stay up to date on information regarding oak wilt in Canada, visit the Canadian Food Inspection Agency website. |
As part of Burlington's Integrated Pest Management (IPM) program, Forestry staff assess sites annually across the city and conduct egg mass surveys to determine areas where natural processes can no longer keep pest population levels down on their own. Although healthy trees can generally withstand repeated defoliation, trees which are already in distress from problems such as acute drought, compacted soils, diseases or other pests may die. Generally, healthy trees which are defoliated in spring, will leaf out again by fall. Spongy moth populations tend to be cyclical, with peaks every 8-12 years, followed by dramatic population decline of the pest
Treatments are only used when populations exceed accepted thresholds. Treatment of the insect populations below threshold levels. The treatment option commonly used is BtK (Bacillus thuringiensis var. kurstaki), a bacterium found naturally in soils. BtK works only against larva of the target species of insect; it does not affect plants, animals or people. BtK is one of the few organic treatments acceptable to organic growers as it is a naturally occurring biological organism.
Help reduce Spongy (Gypsy) Moth populations
| How to create a burlap tree band |
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Burlap banding is an effective way to help reduce the population and damage done by spongy moths (formerly known as the gypsy moth). Follow our steps below or watch the following banding demonstration video.
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| Wrap the tree with burlap |
| Wrap a piece of burlap about 8-12 inches wide around the tree about 4 feet from the ground. |
| Tie the burlap to the tree |
| Tie it with a piece of string so the burlap flops over the front of the burlap to trap the caterpillars and another tie around the bottom. |
| Gather and destroy captured caterpillars |
| Gather the caterpillars each and place them in a bucket of warm soapy water for 3 days, or squish them. |
Spongy Moth Frequently Asked Questions (FAQs)
Are you spraying this year? |
| No, we’re not spraying in 2022. |
Why aren't you spraying this year? |
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Experts did an egg survey and found that the numbers will be below the danger threshold for spraying. Most mature trees can survive a spongy moth infestation. We will survey each fall to determine if it is needed for 2023. Spongy moth populations are cyclical and localized, with populations being higher or lower in different areas of the city during different years of that cycle. Most trees affected by spongy moth recover and grow new leaves after defoliation (losing their leaves). However, additional stresses such as salt damage, soil compaction or multiple years of defoliation can lead to decline. |
I have a lot of eggs/caterpillars. What can I do? |
| Sticky banding and burlap banding can help prevent the caterpillars from crawling into the canopy. There are some good videos online that can help. Some landscape and arborist companies can also do some spraying, but this will be at the homeowner’s cost. |
Can you spray my home or local park? |
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We recognize that their numbers might seem high and they are unpleasant, but we cannot spray this year as the deadline for federal and provincial permission passed months ago. Experts have also told us the numbers are below the dangerous threshold. |