Understanding and identifying the most common ailments trees face will make it easier to manage the impacts of disease. Early detection is the best way to prevent future tree failure because of tree disease or insect infestation.

Let’s go over some of the most common tree diseases and how to identify them.

What Is Your Tree Supposed to Look Like?

One of the most vital steps in recognizing if disease is present is knowing what your tree is supposed to look like to begin with. It is helpful to research what a tree will look like through different stages of growth and what the expected size and shape of the tree will be once it reaches maturation. This information is also important to know before you plant any new trees, so you can ensure they have the right space and proper conditions to grow into their full potential.

Good health indicators for deciduous trees include lush leaves that are the appropriate color for the season they are in. For evergreens, the branches should be full of green needles. The trunk should be in good condition as well. The bark on a healthy tree looks consistent without any holes, inclusions, or cracks. Branches should also be growing in an even pattern from the stem of the tree.

Have There Been Any Abnormal Changes?

Knowing the factors that point to a healthy tree makes it easier to spot when something is not quite right. If you have noticed any abnormal changes in your tree’s appearance, it is prudent you do not just shrug it off. The common indicators of disease are generally easy to recognize if you know what to look for.

Common Diseases & Indicators

Leaf Rust:

Tree rust is a fungal infection that attacks the leaves on the tree. Orange, gold, or reddish spots appear on the leaves and eventually rupture the leaf surface. There are several kinds of fungi that lead to leaf rust, though they tend to be specie specific. This means there is little concern that the infection will spread to other tree types in your yard (though it will likely spread between trees of the same species, so treatment should be applied as quick as possible).

Fire Blight:

Fire Blight is caused by a bacterial infection (Erwinia amylovora). Trees that have become infected with Fire Blight will have drooping branches, with sudden withering of the leaves and blossoms. Cankers often appear on the trunk, and the bark may look as if it has been burnt (hence the name). Fire Blight can be a terminal diagnosis for trees and other plants (especially the Rosaceae family) and the warm, humid climate in Toronto can make it challenging to control. However, early interventions, especially when employed in winter when the bacterium is dormant, have proven successful to stop the spread.

Dutch Elm Disease:

One of the early indicators of Dutch Elm Disease, or DED, is the wilting, curling, yellowing, and premature falling of leaves on the upper branches of an Elm tree. DED is a fungal disease that is spread by elm bark beetles and was introduced to North America in the early 1900s. Because the Elms here do not have any natural resistance to the disease, they have been severely impacted. Integrated pest management systems have helped to slow the spread of DED and protect the vulnerable Elm population.


Anthracnose is another fungal disease that affects trees. This group of fungal diseases cause dry brown or black spots on the edges of leaves. During rainy seasons, anthracnose can spread very quickly which is why early detection and intervention are so important.

Emerald Ash Borer:

The Emerald Ash Borer is an invasive insect species that affects Ash trees. Female beetles lay eggs under the bark of the tree. When the larvae hatch, they feed on the tree and usually overwinter in the prepupae stage. In spring, they fully transform to adult beetles and emerge from the tree. You can recognize the distinctive “D-shaped” holes left behind in the bark from where they exit. Another sign of Emerald Ash Borer infestation includes the thinning of the leaves at the crown of a tree.

Consult the expert

It is essential to address any possible infections or infestations immediately. Waiting too long to apply treatment will likely lead to the continued spread of disease and the eventual death of your trees. Certified arborists have extensive training in diagnosing tree disease and have a wide variety of treatment options at their disposal.

Contact Local Arborist today to inspect your trees for disease. Our team of tree care experts are here to help!

Local Arborist is a professional tree care company in Toronto that specializes in tree disease and pest management. Contact our friendly team today for a free estimate on tree disease treatment.