Common Pests and Diseases

A tree is a living thing. It needs nutrients, water and sunlight to survive. There are many pests and diseases that can affect trees including insects, fungi and bacteria.

Ash-Leaf Cone Roller

Ash-Leaf Cone Roller:
These insects mainly do cosmetic damage to ash trees with little harm to the tree. Ash-Leaf Cone Rollers will enter onto the green leaves as caterpillars, where they will roll the leaves into cones, and emerge as small moths. The City of Edmonton does not recommend pesticide use in managing this insect.

Black Knot Disease in a tree

Black knot:
Most commonly found on cherry trees, particularly Schubert Chokecherries, and is spread through its spores during warm wet weather by wind, insects, and birds. Black knot is a fungal disease that forms swellings on branches and the base of stems. It will stunt growth and kill the tree if not properly managed. Trees infected with black knots should have infected branches pruned off and burned. Pruning equipment must be sterilized after each cut to prevent the further spreading of the disease.


Birch leafminer larvae

Birch Leafminers:
Birch leafminer larvae feed on leaves, leaving a blister-like appearance, and can damage most of the leaf. The City of Edmonton recommends pruning deadwood and removing branches that rub against one another as a preventative measure.


Dutch Elm Disease

Dutch Elm Disease:
Dutch Elm Disease is a fungus that is transported by elm bark beetles and is commonly spread in the deadwood of Elm Trees. Although Edmonton does not have a Dutch Elm Disease issue, homeowners and municipalities must be vigilant to prune all deadwood in the winter months, as this is when the beetles are dormant and will not infect new tree wounds.

Fire Blight bacteria on leaves

Fire Blight:
Fire Blight is a common bacterial disease in Edmonton and the prairie provinces that is found in crabapples, roses, mountain ash, hawthorn, saskatoon, and other fruit trees. It is recognizable by its orangish/bronze leaves and wilting branches. Insects, birds, rain, and wind all spread the disease. To manage Fire Blight, infected branches should be pruned and properly disposed of. Pruning equipment must be sterilized after each cut to prevent the further spreading of the disease.

Larger Boxelder Leafroller Moth

Larger Boxelder Leafroller:
Larger Boxelder Leafrollers are caterpillars that feed on the leaves of maple trees, particularly Manitoba Maples. The caterpillars roll up the leaves with silk during their feeding and can give trees an unappealing look. The leafrollers can defoliate a whole tree, but this does not generally lead to tree fatality.


Black Mountain Pine Beetle

Mountain Pine Beetle:
In recent years, the Mountain Pine beetle has killed hundreds of thousands of pine trees in forested areas northwest of Edmonton. Although they haven’t been detected in the Edmonton corridor, municipalities must be aware of the threat that the Mountain Pine Beetle can have on pine trees. The Mountain Pine Beetle kills trees by emitting a blue stain fungus that clogs tree tissue from circulating water and nutrient uptake. Pine trees that are infested by the Mountain Pine Beetle are burned to kill off larvae, pupae, and adult beetles.

poplar tree borers

Poplar Borers:
About an inch in length in Adult Maturity, Poplar borers emerge in mid-spring and will lay their larvae within the bark of poplar trees. From here larvae bore into the truck leaving a pile of sawdust at the base of a tree or tree branch. The best prevention of poplar borers is to ensure that poplar trees remain healthy with adequate water so that they don’t find their way into the bark of trees during drought-type conditions. Poplar Borers mainly affect Trembling Aspen, Balsam Poplar, Cottonwood, and Willow Trees.


Satin Moth

Satin Moth:
Although relatively uncommon in Edmonton and the surrounding areas over the past few years, the Satin Moth is an insect that homeowners and landscapers should look out for. Traditionally, the Satin Moth has most negatively affected poplar trees, feeding and inhabiting the leaves. To prevent further harm to trees, homeowners can scrape off the eggs that are formed at the lower base of the truck of the trees.

Speckled green fruit worm

Speckled green fruit worm:
These caterpillars lay their eggs on the leaves and twigs of trees. They feed upon the leaves of trees and can defoliate trees if not managed properly. They mainly affect trembling aspen and willow trees.

piny Ash Sawfly larva

Spiny Ash Sawfly:
The Spiny Ash Sawfly affects younger ash trees by feeding on leaves to produce holes and can consume the entire leaf.


Yellow-Headed Spruce Sawfly:
The Yellow Headed Spruce Sawfly attacks spruce trees, particularly young spruce trees in which larvae eat new needles working their way from the top of the tree downward. Insecticides may prove to be an effective agent to kill this invasive species if applied in mid to late June.