Learn more about Toronto's forest pests, diseases and threats by reviewing the factsheets below.
Common insect pests that are a threat to Toronto's trees and urban forest include:
Aphids are small soft-bodied insects that feed on plants by sucking sap from leaves and stems.
The Asian longhorned beetle (Anoplophora glabripennis) is a very serious threat to the hardwood trees of North America.
The birch leafminer (Fenusa pusilla) is included in a group of insects known as sawflies.
The bronze birch borer (Agrilus anxius) is a native, North American beetle that can cause serious damage to a host of birch trees.
The bronze poplar borer (Agrilus liragus) is a flat-headed borer that feeds on poplars and is native to North America.
The carpenter ant (Camponotus pennsylvanicus) is a social insect and lives in colonies. They nest in wet wood in the cavities of trees.
The Eastern tent caterpillar (Malacosoma americanum) is a native insect that rarely occurs in large enough numbers to cause tree death in Toronto.
There are two species of bark beetles that feed and breed on elm trees, the smaller European elm bark beetle (Scolytus multistratus), and the native elm bark beetle (Hylurgopinus rufipes).
The elm leaf beetle (Xenthogaleruca luteola) is originally from Europe and was first discovered in Ontario in 1945.
The elm leafminer (Fenusi ulmi) is a European insect that has been known in North America since the late 19th century.
The Emerald Ash Borer (EAB) is an introduced insect pest from Asia that attacks and kills all species of ash (genus: Fraxinus) trees.
European gypsy moth (Lymantria dispar) is a defoliating insect that can severely weaken or kill trees. It is a major introduced pest to North America.
Fall cankerworm (Alsophila pometaria) is a native insect, and can be one of the most damaging defoliators of Toronto’s urban forest.
There are several species of plant bugs and leafhoppers that feed on honey locust (Gleditsia triacanthos).
Japanese beetles were introduced to North America in 1916. They are a voracious eater of the leaves and fine roots of over 300 different species of plants, grasses and trees.
Lace bugs are a native North American insect that feeds on a wide range of trees.
The eastern subterranean termite was introduced to Toronto in 1938 and has since become established in homes throughout the city.
Common diseases that are a threat to Toronto's trees and urban forest.
Apple Scab is one of the most serious diseases of apple and ornamental crabapple trees.
Ash anthracnose is a common disease of ash trees, caused by the fungus Apiognomonia errabunda.
Beech bark disease is a devastating disease of beech tree and is caused by a complex of a beech bark scale (Cryptococcus fagisuga) and species of Nectria fungi.
Black knot is a disease of Prunus species that causes twig and branch swelling and discolouration, resulting in girdling and dieback of branches and sometimes the main stem.
There are many different types of cankers that affect a broad range of trees.
Cytospora canker is one of the most common and damaging diseases of spruce.
Dutch elm disease (DED) is the most devastating disease of elm trees in North America.
Eastern filbert blight is caused by the fungus (Anisogramma anomola) and is indigenous to northeast North America.
Fire blight can be a serious disease that affects many trees and plants in the Rosaeceae family.
Leaf blotch of horse-chestnut is a leaf disease caused by the fungus Guignardia aesculi.
Oak Anthracnose is a disease affecting oak trees caused by the fungus Apiognomonia quercina.
Oak wilt, caused by fungus Ceratocystis fagacaerum, is a serious disease of oak trees.
Pear trellis rust is cause by the fungus Gymnosporangium fuscum. The pear trellis rust fungus has been introduced to southern Ontario in recent years.
Powdery mildew is a common foliar disease of many tree species.
A large number of scales feed on trees by sucking sap from leaves, twigs or stems.
Sudden oak death (Phytophthora ramorum), is a disease affecting species of oak trees caused by a soil borne, fungal-like organism.
Sycamore anthracnose is the most serious disease of sycamore trees.
Tar spot is a fungal leaf disease that may occur on several plants, but it is most common on maple.
Verticillium wilt is a vascular disease caused by the soil-borne fungus Verticillium dahlia.
Hazards and other threats to Toronto's trees and urban forest include:
The beaver (Castor canadensis) is the largest rodent in North America. In Ontario, they have been known to eat almost every tree and shrub species available.
Bees are important pollinators and honey producers. Wasps and hornets are considered beneficial insects because they feed on a large number of insect pests.
Galls are unusually-shaped formations that grow on plants including trees.
Girdling roots are roots that grow around other roots or around the main stem of a tree.
Mechanical injuries are one of the most common causes of dieback of trees in an urban environment.
De-icing salt used in winter to provide safe road and walking conditions can cause significant damage to trees and other vegetation.
Water is vital to trees. Without water a tree cannot maintain its physiological functions and will die.
Wood decay is a process of wood disintegration that is caused by fungi or other micro-organisms.