Town of Okotoks Open Spaces: Pest Alert Fire Blight

3559_fire blight 1This devastating and highly contagious bacterial plant disease is firmly established in Okotoks. Fire blight is declared a pest under the Alberta Pest Act and must be removed from affected trees and shrubs.

Susceptible trees and shrubs: Mountain Ash, Hawthorn, Apples, Crabapples, Cotoneaster hedges, Pear. Please inspect your trees and shrubs!

Symptoms: Wilted leaves and blossoms remain on curled branches that appear scorched by fire. Look for this to happen early in the growing season. Cankers along the branches form creating sunken areas on bark that are discolored with exfoliating bark. These cankers may also show the organism, which is a yellow or brown ooze present in the growing season.

Treatment: Managing this disease can be difficult but there are some things that we can do to help control the spread of the disease. First of all, avoid planting susceptible species and if you do, keep your numbers down because they require annual pruning maintenance to keep them healthy. The Town of Okotoks currently has these susceptible species identified for limited use. Hawthorn appears to show the most resistance of the susceptible species.

3560_fireblight2Cotoneaster usually has an extremely high incident rate because it is sheared. Shearing is stressful to plants! It promotes soft lush growth and creates rough cuts on the branches leaving many points of entry for the disease to establish. Furthermore, try other dwarf plants for hedges instead, like burning bush (Euonymus spp.), dwarf lilac, dwarf barberry, etc. Planting these dwarf species for hedges can reduce or eliminate shearing which can create a healthier plant. Keeping the plants healthy is critical if you choose to use susceptible plants. Watering, mulching (promotes root growth) and proper pruning will help minimize the spread and introduction of the disease. If you notice diseased branches prune the branch at least 12 inches below the infection. Be sure to prune in dry conditions, use sharp tools and prune the affected areas last if there is other pruning being done in the plant. As a minimum, disinfect your tools between plants. Infected branches should be burned or buried to effectively stop the disease cycle. It is strongly recommended to use a certified arborist because over pruning or improper cuts can also weaken the plant.

Call the Horticulture Hotline at 403-938-8031 to speak with our Horticulture or Urban Forest Specialist for further information. Email: