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Learn About Invasive Species

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Forest Pests and Pathogens


For more information regarding invasive forest species visit www.forestinvasives.ca. Forest Invasives includes comprehensive information on invasive insects, diseases, and plants that threaten our forests and greenspaces; educational webinars that connect audiences with expects to highlight concerns and management strategies; instructive videos that outline detection procedures; and helpful tips for land and home-owners.

Forest Pests


Invasive forest insects are a problem for all types of forest: urban, commercial, and natural. Invasive insects are spread largely in part by humans, making urban centres prime location for an invasion to start. The urban forest increases property values, reduces energy costs for homes with trees near them, improves air and water quality, and give aesthetic value. Once an invasion takes hold it can easily spread out into the natural and commercial forests. The natural forest provides a vast quantity of environmental services, as well as holding intrinsic social values (recreational use, Aboriginal culture, national identities). The commercial forest is a pivotal economic need for Canada, it not only provides a significant portion of our GDP but the forest industry is the source of a lot of jobs. Invasive species are a large financial cost to the forest industry, Canada’s annual timber losses due to invasives are estimated at 61 million m3 which is equivalent to $720 million in losses (Canadian Action Plan for Invasive Alien Terrestrial Plant and Plant Pests (CFIA, September, 2004).  The detrimental impacts on trees by invading insects do not stop with the trees it effects every aspect of the ecosystem.


Asian Long-horned Beetle

Asian long-horned beetles (ALB) are an invasive forest pest that attacks a wide variety of hardwood trees including maples, poplars, birches, and willows. Adult beetles are between two and four centimetres and shiny black with large irregular white spots on their backs. They have bluish tinged legs with white patches, and black and white antennae as long as their body. Larval ALB are cream white, round, segmented grub. ALB causes leaking sap, leaf drop, and branch dieback in its host tress; these symptoms lead to a decrease in hardwood species in infected areas. The affected trees make up a large part of Ontario’s forest and maple syrup industry and their loss could mean huge economic losses. As well as the ecological losses of many important forest species who rely on the hardwood trees for habitat. To remove ALB infestations, all the trees affect and those around the area must be cut and chipped. Do not move firewood or nursery trees as this can quickly spread ALB to unaffected areas. Learn more about ALB at www.forestinvasives.ca.

Fact Sheet

Emerald Ash Borer

As its name suggests emerald ash borer (EAB) is an invasive insect that uses ash trees as a host plant for larval development and feeding. Adults are narrow and 8-14 millimetres; they are metallic green with bright red patches under their wings. Larvae are cream coloured with a brown head and are two to three centimetres long. The affected ash trees have characteristic D-shaped exit holes from adult beetles emerging. They also have dieback, yellowing of foliage, vertical cracks, and shoots that grow out of the lower trunk. EAB infestations kill 99% of ash trees affected and all infested trees are cut and burned. The loss of ash trees causes changes in forest structure and puts native species that use the ash trees at risk. Some chemical treatment methods are in place to inject trees with an EAB specific insecticide but in order for it to be effective it must be administered shortly after infection. The use of wasps as a biocontrol has been approved to help reduce the EAB populations. Learn more about EAB at www.forestinvasives.ca.

Fact Sheet

Brown Spruce Long Horn Beetle

Brown Spruce Longhorn Beetle (BSLB) is a small brown flying beetle (no more than 2.5 centimetres) with long reddish antennae, which infests spruce trees. The beetles lay their eggs in the tree and the larvae feed off of phloem, which carries nutrients throughout the tree. This weakens the tree which then gets reinfested every year until they die (one to five years). The movement of spruce products is highly regulated now to slow the anthropogenic spread of BSLS. Currently the only major North American BSLB outbreak is in Nova Scotia and the infestation is being monitored closely and there has been significant suppression by NRCan’s Canadian Forest Services through trapping and mating disruption.

Fact Sheet

Mountain Pine Beetle

Mountain pine beetle (MPB) is a small beetle (less than a centimetre) that is native to western Canada and uses lodgepole pine as a host. They are beginning to spread to north east into Alberta, using the jack pine as a new host. This spread could lead MPB further east and into the Canadian Shield. Adult MPB are dark and cylindrical with a distinct separation between their abdomen and thorax. Once MPB bores into a tree and begins to dig galleries the water flow in the tree is disrupted, causing the drying out of the foliage. Initially the needles turn a dull green, then yellow to red, until they eventually drop. The spread of MPB could dramatically impact the forestry industry Canada wide and severely reduce wildlife habitat. Alberta is aggressively managing MPB by aerially surveying trees and removing newly infected trees to try to combat the spread. Learn more about MPB at www.forestinvasives.ca.

Fact Sheet

Gypsy Moth

Gypsy moths and their caterpillars are invasive pests that defoliate hardwood trees such as oak, birch, poplar, willow, and maple. Gypsy moth caterpillars are up to six centimetres long with five pair of blue dots and six pair of red dots running down their back and are covered in long light hairs. Adult male moths are brown with dark markings on its wings. Females are white with dark markings and are flightless. Gypsy moths defoliate and kill the trees that they infect, this impacts the ecosystem services that the trees would give. Also, because a lot of the forest industry relies on these hardwood species, there are large economic losses in affected areas. Because gypsy moths don’t bore into the tree they can be removed; eggs sacks can be scraped off, and caterpillars can be trapped in burlap wrapped around the trunk.

Sirex Woodwasp

Sirex woodwasps are a parasite of a wide variety of pine species; the females lay eggs in the tree in a substance that is toxic to the tree. The adult wasp can be up to three centimetres long with thin bodies and no ‘wasp waist’. Males are black with orange-yellow segments where females have a greyish blue body and reddish legs. When pines are attacked they produce resin to try to kill the invader, so infested trees will have beads of sap running out of oviposition holes. Their needles will wilt and turn yellow and eventually go brown and drop. If the tree becomes heavily invaded it will stop growing and die. Several biocontrol options have been implemented to try to diminish populations. Using a parasitic wasp to hyperparasitize the woodwasps is effective but doesn’t reduce the population enough to stop the spread.

Fact Sheet

Forest Pathogens


Invasive forest pathogens are usually the result of a fungal infection and are a problem for all types of forest: urban, commercial, and natural. The pathogens have the ability to dramatically decrease the population of a single species within the forests which can severely impact the forest functions. The urban forest increases property values, reduces energy costs for nearby homes, improves air and water quality, and give aesthetic value. The natural forest provides a vast quantity of environmental services, as well as holding intrinsic social values (recreational use, Aboriginal culture, national identities). The commercial forest is a pivotal economic need for Canada, it not only provides a significant portion of our GDP but the forest industry is the source of a lot of jobs. The detrimental impacts on trees by invasive pathogens do not stop with the trees it effects every aspect of the ecosystem.
Beech Bark Disease

Beech bark disease (BBD) is an insect-fungus combination; beech scale is an invasive insect that feeds on the bark of beech trees, giving the native canker fungi a way to entre and infect trees. Within 10 years of infection 50-85% of trees die. The scale insect is yellow and up to 1 mm long, it covers itself in white woolly wax that gives the appearance of a wool coating on the tree. Once the tree is infected with the canker fungi it develops deformities, small cankers, and tarry black substance on the trunk that can eventually lead to its death. The beech tree produces nuts that are a main food source for many native species especially black bear. The damage to beech trees also negatively impacts the forest industry, reducing their profits. The loss of beech trees would also decrease the biodiversity and beauty of the forests, causing both environmental and social losses. Learn more about beech bark disease at www.forestinvasives.ca.

Butternut Canker

Butternut canker is a disease that affects the butternut tree, it is caused when a specific fungi gets under the bark and causes cankers to form on the trunk, branches, or exposed roots. These cankers form as large black spots from the fungi hyphae; the infection can spread via spores all around tree, causing dieback and eventually death. The introduction of butternut canker has resulted in a dramatic decrease in butternut populations as well as causing a loss of biodiversity in our forests. The seeds produced by the butternut tree are an important food source for native species including birds and small mammals. Butternut is also a high quality wood for woodworking and cabinet making, the cankers severely damage the quality of the wood making it undesirable. Butternut trees produce nuts that humans have been consuming for hundreds of years as well as a natural yellow dye, the loss of butternut trees will cause social losses. Learn more about butternut canker at www.forestinvasives.ca.

Fact Sheet

Dutch Elm

Disease Dutch elm disease is a fungal disease that is spread by both a native and introduced beetle. The beetles burrow through the tree, creating galleries, and spreading the fungus throughout. The fungus blocks sap movement in the elm trees which causes; yellowing and wilting of leaves, brown stains in the sap wood, and eventual branch dieback. Elms are popular urban trees that are used to line roadsides, due to Dutch elm disease they die off, reducing property value and costing money to have removed. It also reduces native biodiversity and wildlife habitat.

Oak Wilt

Oak wilt is a vascular disease caused by a fungal infection. The fungus produces mats under the bark that result in discolouration of the sap wood. The tree stops being able to transport fluids and the leaves eventually turn yellow and fall off. Trees usually die within a year of being infected, however, some trees do show resistance and survive. Oak trees are a very important forest species; they offer soil stabilization, erosion prevention, and air quality improvement. They are also needed for native wildlife by providing habitat and food. The tree damage and loss decreases the economic gain from oak harvesting. Learn more about oak wilt at www.forestinvasives.ca.

               Hikers Action Plan

Think about the threat of invasive species when planning your next hike. Make sure your love of nature doesn’t accidentally harm the next woodland you visit.

1. Stay on the path

Stay on the paths designated for hiking in natural areas to avoid picking up seeds from the forest that shouldn’t be spread elsewhere.


2. Clean your gear

Check all of your hiking gear at the end of your outing for plants and mud that might be carrying invasive plant seeds


3. Groom your pet

Make sure your pets don’t bring back an invader from the forest. Look over your pet at the end of the trail and wash off any mud. Keep invasive seeds form using your dog as a way to invade new areas.


4. Report all invaders

Call the Ontario Federation of Anglers and Hunters’ Invading Species Hotline at 1-800-563-7711 to report an invasive species sighting. Or download the EDDMapS Ontario app to report an invader on the spot.