County warns about black knot

By Sean Feagan, Local Journalism Initiative Reporter

A tree disease caused by a fungus has been identified in Wheatland County and, if left unchecked, may result in the stunting or death of trees.

Black knot, caused by the fungus Apiosporina morbosa, is a disease affecting certain fruit trees (in the genus Prunus), including cherries and plums. The stems of affected trees show a blackish growth or swelling.

On Feb. 17, Wheatland County announced its maintenance crews identified black knot in some of its communities. The county’s hamlet operations foreman said black knot was seen a few years ago, and while it does not seem widespread, residents should be aware of it and how to deal with it, wrote Mackenzie Maier, the county’s communication specialist, in an email.

While the disease is considered common and widespread in Alberta, if it is left to progress, it can disfigure and reduce the growth of branches, sometimes leading to the death of the tree. It also stresses the infected tree, leaving it more prone to infection from other pathogens.

The county cut the infected portions out of the trees areas it maintains. However, diseased branches were identified on private properties, so the county is asking landowners to assess their properties for its presence and remove any infected materials.

To control black knot, all knot-bearing branches should be pruned out in late fall, winter or early spring, when plants are dormant and knots visible. Infected branches should be removed six to eight inches below the knot. To avoid spreading the spores of the fungus, shears should be cleaned and disinfected after use. Diseased wood should be either burned or removed from the site, as they may release spores for up to four months after removal.