Tree diseases can spread quickly and cause long-term damage if they go unnoticed. In Calgary’s changing climate, trees are exposed to stress from temperature swings, moisture changes, and pests, which makes them more vulnerable to infections. Knowing the most common diseases and their warning signs helps homeowners protect their trees and prevent further damage.
Dutch Elm Disease
Dutch Elm Disease is one of the most serious tree diseases in Alberta. It affects elm trees and is caused by a fungus spread by elm bark beetles or through root connections between trees.
Signs to look for:
- Leaves turning yellow or brown in summer
- Wilting and curling leaves
- Branches dying from the top down
- Brown rings visible under the bark when a branch is cut
This disease can kill a mature elm within one or two seasons if not removed.
Black Knot
Black Knot is common in chokecherry, mayday, and other ornamental trees. It appears as hard, black, swollen growths on branches and twigs.
Signs to look for:
- Dark brown or black lumps on branches
- Swollen, rough growths that enlarge over time
- Twisted or deformed branches near the infected area
Cutting out the infected sections is the most effective way to stop it from spreading.
Fire Blight
Fire Blight affects trees like apple, pear, mountain ash, and crabapple. It is caused by bacteria and spreads during warm, wet weather.
Signs to look for:
- Leaves and shoots appearing burned or scorched
- Branch tips curling into a hook shape
- Oozing sap or sticky droplets from infected branches
- Sunken, dark cankers on the bark
This disease can spread quickly during spring and early summer.
Cytospora Canker
This disease affects poplar, spruce, and willow trees. It is caused by a fungus that infects stressed or damaged trees.
Signs to look for:
- Sunken, discolored areas on the trunk or branches
- Oozing amber or white sap from infected spots
- Dead branches or thinning foliage
- Rough, cracked bark around the canker
Proper pruning and stress reduction can help prevent further spread.
Needle Cast Disease (Spruce and Pine)
Needle Cast is a fungal disease that affects spruce and pine trees, especially when they grow in shaded or damp areas.
Signs to look for:
- Yellow or brown needles starting from the lower branches
- Needles falling prematurely
- Dark fruiting bodies on the underside of needles
- Thinning branches from the bottom up
Improving airflow and removing infected branches can help control it.
How to Protect Your Trees
While some infections can be managed, severely diseased trees may need to be removed to protect nearby trees and property. Here are ways to reduce risks:
- Prune trees during dry conditions to prevent infection
- Remove and dispose of diseased branches properly
- Avoid overwatering or damaging tree roots
- Keep trees healthy with proper watering and soil care
- Monitor trees regularly for early symptoms
Final Thoughts
Tree diseases can cause serious damage if left untreated. Early detection and proper care help protect your trees and prevent the spread of infection. If a tree shows signs of severe disease or decay, professional removal or treatment may be necessary to keep your property safe.
