Fungus in leaves can eventually kill trees

Hey there, time traveller!
This article was published 22/06/2012 (4336 days ago), so information in it may no longer be current.

In September, I wrote about problems with anthracnose disease in ash trees in southern Manitoba. As with many tree diseases, the conditions that allow it to infect and damage trees increase each year. This disease continues to kill leaves, twigs and branches — even the entire tree.

In addition to ash, deciduous trees such as oak, elm, poplar and maple can become infected with this disease. I have taken photos of this disease on the leaves of other tree species.

Initially, this fungus affects the leaves, usually as spots or blotches and often causing the leaves to curl around the diseased area, especially if it’s on the side of the leaf.

Infections on leaves of susceptible trees are more severe in areas where prolonged spring rains occur after new growth appears. Anthracnose fungi need water in order to spread their microscopic spores and infect new leaves; they don’t spread during dry spring weather. Wet, cool springs followed by hot, dry summers are ideal for the spread of the anthracnose fungi.

Right now, one can see the leaves of stressed trees have curled, with tattered leaves and brown areas killed by the fungus. Anthracnose also can attack and kill twigs and branches. Ash trees are hit hardest by this disease in southern Manitoba, and it has caused numerous large dead branches in the crowns of thousands of trees.

Anthracnose disease can show up as a twig fungus, which can cause the twigs to grow abnormally and die. This abnormal growth is called a “witch’s broom;” however, the technical term is epicormic twigs. There is no known control for this component of the disease. All that can be done is to prune off the dead twigs.

Unfortunately, the longer these problems are ignored, the more these trees get stressed, causing large branches to eventually die. In many instances, the death of the tree eventually follows.

Leaf anthracnose can be controlled by spraying an approved fungicide, such as one of the copper spray products, twice about two weeks apart in June and early July, if the weather permits spraying. In the last couple of years, wet Junes have made copper fungicide treatments next to impossible for many hundreds of property owners. Treatments need to be done annually for three consecutive years for badly infected trees.

Michael Allen, M.Sc.F., RPF, is a consulting urban forester and certified arborist. He owns Viburnum Tree Experts, a Manitoba company that provides objective assessments of the condition and the care required for trees and shrubs on home and business landscapes. He can be reached at 204-831-6503 or viburnumtrees@shaw.ca. His website is www.treeexperts.mb.ca