Ontario is home to a wide number of tree species. Whether in forests, lining streets, or just in our backyards, there are always diseases, insects, and invasive species that are threats to the health of our trees.
Below are some of the most common threats to Ontario’s trees and issues we see regularly during our inspections and assessments at P & A.
Dutch Elm Disease
Dutch Elm disease is one of the most devastating tree diseases in Ontario and across North America. It attacks elms in particular and if left untreated, will kill the tree eventually. Infected elm trees will have leaves that are wilting, curling, and turning yellow, and progressively falling from the tree.
The fungus is carried by beetles from tree to tree. If detected early, branches can be pruned and the tree can be treated with fungicide to help curb it. Avoid pruning trees with Dutch Elm disease from April to October. It’s best to contact a professional for this work to ensure the rest of the healthy branches are not damaged.
Dutch elm disease is the most devastating disease of elm trees in North America. Beetles carry the fungus that causes this disease.
Anthracnose
Anthracnose is a disease present on the bud of the twig that spreads during damp cool spring weather. It usually affects ash, maple, and oak trees.
While non-fatal to otherwise healthy trees, signs of an infected tree include dry brown and black blotches on the edge of the leaves that spread to the whole leaf. The leaves will drop in the spring and may return in June or July again.
While not fatal alone, if a tree’s health is already compromised, anthracnose can cause further stress on the tree and lead to its death. Prune diseased branches and rake and dispose of leaves and fruit in the fall since the disease can live in them over the winter and re-infect the trees in the spring.
Gypsy Moth
We’ve spoken a lot about the gypsy moth in recent months because it wreaked havoc on trees across Ontario in the summer of 2020. If left untreated or without prevention, a bad Gypsy Moth infestation can kill a tree in as little as two years.
It’s best identified by its egg masses. In groups of 400-700 eggs, they are tan in colour and suede-like in appearance. They are about 2.5cm in diameter on the trunk or limbs on a tree and easily identifiable in late fall or winter. The following spring, the eggs will hatch and start to feed on tender leaves, eventually stripping the tree of its leaves. Scraping these egg masses or wrapping the tree in folded burlap can help prevent the larvae from reaching the leaves.
Gypsy moth larvae feed quickly and can decimate forests in as little as two years.
Emerald Ash Borer
Emerald Ash Borer is a massive threat to Ontario’s ash trees. Already it has wiped out ash populations in cities across Canada. Larvae hatch in the spring and tunnel under the bark, eating the tissue and disrupting the flow of nutrients. Leaves first begin thinning at the top of the tree, eventually spreading downwards. Once a tree is infested with Emerald Ash Borer, it will most likely die.
Injection treatments are available for ash trees to prevent the infestation, but they must be administered before an infestation occurs. The best way to prevent the spread is to not move firewood between cities and regions so as to keep uninfested ash trees in Ontario safe.
Unfortunately, it may only be a matter of time before ash trees are completely gone from Ontario forests.
Sudden Oak Death Syndrome
Sudden Oak Death Syndrome hasn’t yet made it to Ontario, but is traveling east across the United States and is likely to arrive in Ontario at some point. Not much is known about this disease yet, except that it’s a soil borne, fungal-like organism that leads to cankers oozing red and black, and causes leaves to turn pale yellow or brown. It affects species of oaks.
The best way to prevent this disease is by monitoring plants, trees, and soil that are brought into Ontario from the United States, as the disease can spread easily from plant to plant.
Beech Bark Disease
Beech bark disease is currently a massive threat to beech trees in Ontario. It’s caused first by something called Beech Bark Scale, which weakens the tree by making wounds in the bark and limbs. When the tree is weakened from Beech Bark Scale, it provides the opportunity for the fungus (carried by an insect) to enter the wounds, spread, and kill the tree.
Beech Bark Scale can be treated if the tree is not yet infected with the fungus. It appears as white, wooly wax on the trunk of the tree. This can be treated by applying dormant oil after the leaves drop in the fall.
If the tree is infected with the fungus, the tree will die and will need to be removed. If the wax turns yellow, the leaves don’t grow to their full size, or the tree is oozing brown, it is likely infected with the fungus.
Oak Wilt
This disease affecting all oak tree species has recently been detected in Southern Ontario near the border with the United States, and may spread quickly throughout the province if the proper care is not taken.
Once a tree is infected with oak wilt, the tree will die. It spreads through root grafts with neighbouring oak trees and by sap feeding beetles. It’s imperative that you not move firewood between cities or regions to help prevent the spread of Oak Wilt.
You can spot Oak Wilt easily because the leaves turn a yellow-bronze colour and drop early, in July or August. The bark can also split due to the growth of fungal mats under the bark. If you believe your oaks have this disease, act fast to prevent the spread and call a tree care company.
Fire Blight
Fire blight is a common disease that affects many species, include apple trees and pear trees. While not fatal to otherwise healthy trees, it can cause immense problems with the fruit of these trees and cause the tree to be more susceptible to damage and other diseases.
A tree with fire blight will appear to be burned. Fruit can be shriveled, dark cankers or lesions will form, ooze can form on twigs, and leaves will turn brown and curl into a candy cane shape.
If a tree has fire blight, to prevent it from spreading to other trees, prine the infected area and sterilize the tools with rubbing alcohol between cuts. Dispose of the prunings immediately. Bacterial spray from a professional may also help if fire blight is affecting your apple orchard.
Cankers
Cankers in general can affect a broad range of trees. It refers to a fungal or bacterial infection that weakens the tree by girdling the trunk and limbs, making it vulnerable to other diseases and pests.
Cankers can appear on branches, stems, or trunks and look like dark lesions that sometimes ooze. Leaves may wilt or needles may brown.
Particularly in Ontario, Butternut Canker is a disease that affects the endangered butternut trees in the province.
Stay Ahead of your Tree Health
If you’re worried about the health of trees on your property, P & A can help. We can diagnose insect infestations or diseases in your trees and provide a management plan to help you keep your trees healthy.
Get in touch with us today if you’re concerned about your trees!