Tips for combating Black Knot in Lacombe

The City of Lacombe is advising residents that Black Knot (Apiosporina morbosa) – a deadly tree fungus – is spreading rapidly across Lacombe, and can kill cherry trees in just a few years if residents don't take immediate action.

The fungus spores are spread by splashing water, wind, birds, and insects. The fungus causes greenish brown to black swellings on a tree's branches and stems, deforming and reducing their growth. Heavily infected trees often become stunted and may eventually die from the disease.

Residents with Choke Cherry, Pin Cherry, Mayday and Schubert trees on their properties are advised to monitor them regularly, as the infection is easy to spot. Up to 75 percent of these trees in the city are infected.

Catching the infection early and pruning the affected branches when they are in the dormant stage – in early spring or late fall – can usually save the tree; however, be sure to sterilize your pruning shears with rubbing alcohol after every cut to prevent the further spread of fungus spores.

Prune affected branches at least 6 to 8 inches below the infected area. Practice good sanitation by not to leaving any prunings on the ground, as there is a risk of fungus spores being left behind in the debris. Never prune in the rain, no matter how light or heavy, as spores can be released in the air.

If the pruning during the growing season, the infection limbs should be bagged and never transported in open air. Do not compost the infected tree prunings, as they can continue to produce spores for months after being removed. Instead, take the cuttings to the Wolf Creek Recycle Site for proper disposal, or to the Prentiss Landfill east of the city.

The City is currently undertaking a community-wide tree pruning campaign in public parks and open spaces to combat the spread of the disease. For more information on managing Black knot on your property, please contact the Parks Department at (403) 782-1297.


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