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Fire blight

Fire blight is a serious bacterial disease affecting trees and shrubs in the rose family. It can ravage Calgary’s urban forests during humid and warm summer weather conditions. Generally, fire blight is very rare in Calgary since our summers are usually too cool and dry for disease development. However, severe thunderstorms and hail can lead to an outbreak of fire blight.

Fire blight affects primarily the rose family of trees and shrubs. Common members of this family include apple and crab apple, pear, mountain ash, cotoneaster, raspberry, flowering almond, and saskatoon.

Fire blight bacteria can spread a number of ways, including insect transmission, use of contaminated pruning tools and strong winds and rain. Hailstorms help spread the disease by wounding the bark and making the tree vulnerable to infection.


  • Diseased leaves appear red and fire-scorched. Blighted leaves eventually brown and die but remain attached to the tree.
  • New growth exhibits a dramatic downward wilting at the tips.
  • Clear amber liquid may be found oozing from diseased twigs. This liquid is highly charged with the bacterium, which causes the disease. Transferring even a small amount to healthy trees can generate new infections.
  • Some trees may develop secondary infections indicated by bark cankers, which appear as indented, discoloured areas on the branches and trunks. Bark cankers are usually more serious infections and can kill the tree.

What can you do?

The first step to controlling the disease is to prune, remove and destroy all diseased wood. However, pruning can also be a means of transmission. It is critical that you sanitize your tools as you prune. After each and every pruning cut, the cutting blade must be sanitized with a 25% solution of bleach and water (1 part bleach + 3 parts water).

Take diseased branches and other wood to the landfill to prevent re-infection. Do not use fire blight-infected wood in mulch, compost or store as firewood or compost materials. Infected branches will continue to harbour the disease and serve as a potential source of re-infection. 

Bacteria blight: A similar disease

Not all dead leaves and branches are caused by fire blight. A disease known as bacteria blight is commonly mistaken for fire blight. The symptoms of bacterial blight are somewhat similar to fire blight but can also affect lilacs, cherries, apricots, and other types of flowering trees. Treatment for bacterial blight is the same as for fire blight.

We encourage you to contact a tree and shrub-care professional if you have further questions or concerns.