Trees in urban areas are under stress from problems such as extreme temperatures and poor soil conditions. When trees are stressed, they are much more susceptible to insect pests. Exotic pests pose a significant threat to urban trees, such as emerald ash borer. Newly introduced exotic pests are often more successful because they have been introduced without the natural predators or parasites that would normally help keep these invasive pest populations in balance.

Using strategies that help improve tree health and suppress pests will help maintain urban tree populations. Cultural methods, such as those that improve soil aeration, soil organic matter and soil moisture, may help increase the tree's natural resistance to these pests. Cultural methods are an important part of other strategies used for exotic pests including exclusion, eradication, suppression, containment, slowing the spread and management.

This management strategy focuses on two significant insect pests of urban landscape trees in Ontario:

  • emerald ash borer (EAB) on ash (Fraxinus sp.)
  • bronze birch borer (BBB) on birch (Betula sp.)

The following information may also be helpful when managing other insect pests of landscape trees.

For forest pest management information, please refer to the Ministry of Natural Resources and Forestry.


Emerald ash borer (EAB)

Emerald ash borer (Agrilus planipennis) is an exotic, invasive insect pest that has killed millions of ash trees in Ontario, Quebec and the United States. It poses a major economic and environmental threat to urban and forested areas in both countries.

Emerald ash borer is regulated by the Canadian Food Inspection Agency (CFIA) and is known to infest several areas within Ontario and Quebec. The CFIA program is focused on the leading edge of the infestation to slow its spread to help protect Canada's environment and forest resources and keep international markets open.

Emerald ash borer attacks and kills all species of true ash (Fraxinus sp.). With artificial spread, such as movement of infested ash firewood and nursery stock, this insect can quickly infest other areas of Canada. CFIA regulatory measures prohibit the movement of specific materials including any ash material and firewood of all species from specific regulated areas of Ontario and Quebec. Anyone violating these restrictions is subject to a fine and/or prosecution. Report signs and symptoms of infested trees in unregulated areas to the CFIA at 1-800-442-2342 (toll-free).

Bronze birch borer

Bronze birch borer (Agrilus anxius) is a North American insect pest that has damaged and killed tens of thousands of birch trees in Canadian landscapes. It attacks several species of birch (Betula sp.), but is especially devastating on exotic birch species including European white birch (Betula pendula). It attacks native birches such as paper birch (Betula papyrifera) and grey birch (Betula populifolia), mainly when they are under stress (improper soil, site conditions, competition). It is a serious insect pest, often killing trees in just two to three years. It is not a regulated insect pest in Canada.


Monitor trees for signs of stress and boring insect pests that might be attacking the trees by conducting visual inspection by ground, climbing or aerial. Tree-inhabiting borers will cause overall decline of growth. This can result in symptoms such as stunted growth, leaf chlorosis, leaf drop and twig and branch dieback in the crown.

Various life stages of EAB and BBB may be detected depending on the time of year. Woodpeckers will eat boring insects, so woodpecker activity and damage are usually good indicators that trees are infested with insect borers.

Trap systems, such as green and purple prism trap systems, have been developed to attract adult Emerald Ash Borers. Trapping adults will only indicate that EAB is in the area, not which trees are infested. Visual monitoring and destructive sampling are required to confirm EAB infestation in trees. Detection of EAB in urban environments using branch sampling has also been developed by Natural Resources Canada, the Canadian Forest Service in collaboration with the CFIA and the Ontario Ministry of Natural Resources. Branch sampling in open grown, urban ash trees has been used to detect the presence of EAB in asymptomatic trees and has about a 75% success rate.


Signs and symptoms of emerald ash borer

Signs and symptoms of EAB include:

  • dieback (canopy thinning in the top third of the crown, progressing throughout the entire canopy)
  • epicormic shoots (shoots growing from the lower trunk, leaves are often juvenile-looking and larger than average)
  • bark cracking (larval galleries of EAB cause trees to produce callus growth over the galleries which forces over-laying bark to split vertically; callus growth is a defense mechanism for the tree)
  • serpentine larval galleries (larval feeding causes serpentine-shaped tunnels in phloem, just under bark)
  • larvae (white, flattened, highly segmented larvae in larval galleries from late summer to spring)
  • D-shaped exit holes in bark of trunk and larger branches from emerged adults (difficult to detect)
  • woodpecker activity (several species of woodpeckers feed on EAB larvae/pupae, chipping off bark to expose the inner bark and wood in order to find them, leaving large holes in the tree)

Photos and detailed descriptions of EAB can be found at:

Signs and symptoms of bronze birch borer

Signs and symptoms of BBB include:

  • death of the leader (canopy thinning and dieback in the top of the crown, often starting with the leader only, progressing throughout the entire canopy, branch by branch over one to five years)
  • raised, horizontal and zigzag ridges in bark (larval galleries of BBB cause trees to produce callus growth over the larval galleries which forces over-laying bark to become raised; callus growth is a defence mechanism for the tree)
  • white, flat, highly segmented larvae in larval galleries, from late summer to spring
  • D-shaped exit holes in bark of trunk and larger branches, from emerged adults
  • woodpecker activity (several species of woodpeckers feed on BBB larvae/pupae, chipping off bark to expose the inner bark and wood in search of them, leaving large holes in the tree)

Photos and detail descriptions of BBB can be found at:

Management for emerald ash borer and bronze birch borer

Site selection, nutrient and water needs

Landscape trees should be monitored and managed for signs of stress. Proper site selection is one of the most important factors in good tree health. For instance, birch trees are shallow-rooted and thrive on sites with cool, moist soil in the root zone. Quite often, trees are planted in dry, exposed sites with inadequate compacted topsoil and significant competition from turf or other ground covers.

Cultural practices such as root zone aeration, irrigation during establishment and drought, structural pruning, removal of competing ground covers, mulching, supplementing soil with organic matter, fertilizing and protection from mechanical injury and compaction should be carried out to help improve the tree's tolerance to pests. Supplemental irrigation is especially important for trees recovering from pest infestations during the dry summer and autumn months. A slow, gradual irrigation of 15 to 20 mm every 7 to 10 days during hot, dry conditions will help keep trees healthy.

Species selection

Where possible, tree species that are tolerant or resistant to borer pests should be used in the landscape. For example, river birch (Betula nigra) has demonstrated good tolerance of BBB. Blue ash (Fraxinus quadrangulata) has demonstrated good tolerance of EAB when it is growing on its own roots. Landscapes that contain a diverse mix of tree species (biodiversity) will be less susceptible to the impacts of host-specific pest problems like borers. A team of Ontario horticulturalists recently assembled a list of trees for urban landscapes that might be planted as alternatives to ash. The list comprises several species that are noted to be able to survive in some tough urban landscapes.

Removal, pruning and sanitation

Bronze birch borer infestations often begin with branch tip death and usually occur on the leader. Removing and destroying infested branches while the insect is in the larval stage may prolong the life of the birch tree. Infested branches may be removed prior to leaf emergence to help reduce adult emergence and lower populations in the area. Do not prune branches of birch trees once leaves have emerged in spring and early summer as adults will be emerging and the fresh pruning cuts will attract BBB adult females to lay their eggs. There is no evidence to indicate that pruning out infested branches may prolong the life of an ash tree after EAB attack.

Branch trimmings and removed trees that are infested with borers should be chipped or burned as soon as possible to help prevent any tree inhabiting borers from completing their life cycle and infesting other trees. Municipalities with EAB infestations may have established special procedures for handling tree trimmings and yard waste from regulated areas. Contact your municipality for the latest information on disposal of regulated yard waste.

Biological control

There are numerous native biological control agents, such as predators, parasites and pathogens, that use the insect pests that plague our landscape trees as a food source. Examples include woodpeckers feeding on wood boring insects and parasitic wasps that lay their eggs inside the larvae and eggs of wood borers. While there are several species of parasitoids that attack BBB eggs, the level of parasitism is not usually high enough to have any significant impact on the pest population.

When pests are introduced from one area to another (for example, from China to North America), the biological agents that would normally help keep them in check do not exist in the new area. Classical Biological Control is the practice of importing and releasing host-specific natural enemies from a pest's native range to help control populations in the area of introduction.

EAB is native to north eastern Asia, where it is considered a sporadic pest of ash. Populations of EAB in Asia remain low due to resistant host plants, climatic conditions and a complex of natural enemies that exist there. North American and Chinese scientists have been searching for natural enemies of EAB in its native range since 2003. Several EAB parasitoids (small stingless relatives of ants and wasps) were discovered in China. North American scientists are currently evaluating parasitoids from China for biological control of EAB here in Canada and the US. Some of these parasitoids have been released in EAB-infested regions in North America and are being evaluated for their suppression of EAB populations.

Pest control products (pesticides)

Insecticides can be important pest management tools in the management strategy for emerald ash borer and bronze birch borer when trees are at risk and other methods are not adequate to protect trees. Insecticides may be toxic to non-target organisms and may persist in the environment. Insecticides should be used only where treatment is deemed necessary for the tree's health.

Tree injection is a method of application that minimizes the risk of exposure to non-target areas and organisms. In comparison to traditional application methods where the insecticide is applied as a spray application to the exterior of the tree, trunk injections deliver the insecticide directly into the selected tree. Application by trunk injection helps conserve natural enemies of pests as well as other non-target organisms that would be exposed to foliar applications of insecticides.

A pest control product must be registered by Health Canada's Pest Management Regulatory Agency (PMRA) under the Pest Control Products Act and classified under the Pesticides Act and O. Reg. 63/09 by the Ministry of the Environment, Conservation and Parks (MECP) to be sold and used in Ontario. Products must be used according to label directions.

There are a few injectable insecticides registered for use in Canada for the management of EAB and BBB. You can view these pesticide labels on the PMRA's Label Search by searching for the individual pest name under "Search Full Contents of E-labels". These products are used to help protect trees from infestation of labelled pests to maintain the tree health. These injectable insecticides are systemic, which means they are transported upwards through the tree.

Even with systemic insecticide treatment, it can take the tree several years to recover from pest infestation. Since the pests are established in the landscape, re-treatment will be required for continued protection against future attacks. Application costs may make these treatments an option for high value landscape trees, but it is also available for use on trees in forestry production, nurseries, greenhouses and forests where economically feasible.

Studies have shown that it is best to begin using insecticides while trees are still relatively healthy. This is because the injectable insecticides work systemically. The insecticide must be transported within the tree in healthy sap conducting tissue (xylem and phloem). Larval galleries of these boring insects will interfere with the tree's ability to transport water, nutrients and injected insecticides from the trunk to the crown and may result in incomplete protection and efficacy. For these reasons, some researchers suggest that if >50% of the canopy has been lost, it is probably too late to save the tree.

The registered injectable insecticide products contain active ingredients that are toxic to bees or bee brood. Since these products are systemic and can travel up the tree to the flowers, bees can be exposed to residues in floral pollen and/or nectar resulting from tree injections. To mitigate the risk from these tree injections, label requirements state that these products can only be injected post-bloom to flowering deciduous trees, such as ash and birch, to reduce impacts on bee pollinators. Some residues may be carried over into the following season. Do not apply injectable insecticides to trees that will produce food for humans.

Most injectable insecticide products used to manage EAB and BBB are toxic to aquatic invertebrates. Do not contaminate irrigation or drinking water supplies or aquatic habitats by cleaning of equipment or disposal of wastes. Do not mix, load or clean equipment within 30 m of wellheads or aquatic systems.

For best results, application should be made when the tree is actively transpiring (on sunny days), generally May to August, where leaves have emerged and are fully expanded, but preferably before late summer. The ability of the tree to conduct the insecticide up into the canopy may vary with tree species, geographic area, time of day, individual tree vigour or light intensity at time of treatment. If soil moisture conditions are dry, a thorough deep root zone watering prior to treatment will enhance insecticide uptake. Where possible, avoid annual applications of insecticide since the application procedure creates wound sites.

Pesticide use requirements

The Ontario Pesticides Act and O. Reg. 63/09 provide the province's regulatory framework for pesticide management to protect human health and the natural environment. The MECP, through the legislation, regulates the sale, use, transportation, storage and disposal of pesticides. Refer to the MECP website for regulatory information relevant to the use of pesticides and tree care:

More information

The Ministry of Agriculture, Food and Rural Affairs (OMAFRA) nursery crops blog provides current pest management recommendations for the nursery and landscape sectors during the growing season. Information on tree pests and their management can also be found in Ontario Crop Protection Hub.

Contact the OMAFRA nursery and landscape specialist or certified crop advisors for any additional pesticide resistance management and/or integrated pest management recommendations.

For tree care service providers, contact a certified arborist.

Search Canadian-approved pest control product labels for labelled uses on nursery and landscape trees. Product labels can be found on registrant company websites and at the PMRA.


Buck, J.H. and Frappier, S. EAB Program Manual.

Herms, D.A., McCullough, D.G., Smitley, D.R., Sadof, C., Williamson, R.C. and Nixon, P.L. 2009. Insecticide options for protecting ash trees from emerald ash borer. North Central IPM centre Bulletin. 12 pp.

Marchant, K.R. 2011. York Region Emerald Ash Borer Management Plan.

Pest Management Regulatory Agency. 2011. Evaluation Report ERC2011-03. Confidor 200 SL containing Imidacloprid. Publications PMRA Health Canada.