Anthracnose of shade trees

By Katie Drewitz,U of M Extension

With the cool, wet spring temperatures that we have been fighting this year, we have seen an increase in calls to the Extension office with related issues. One of the issues that is incredibly concerning to home owners is anthracnose of shade trees. The good news is that this fungal disease is generally short–lived and does not require treatment in most cases.

Anthracnose is a common fungal disease of shade trees that results in leaf spots, cupping or curling of leaves, and early leaf drop. In Minnesota it is most common in cool, wet springs like the one we are coming out of this year. If your tree leaves are looking unhealthy or your tree has lost most or all of its leaves, there is a chance that it has anthracnose. Leaf symptoms are usually most severe on the lower and inner branches of the tree.

If your tree loses its leaves it is important to rake up the leaves, and dispose of them. It is also important to clean up your leaves in the fall. Anthracnose fungi survive the winter in buds, twigs, fruit, and fallen leaves. In spring, spores are splashed short distances by water or carried in the wind. If weather conditions remain cool and wet, spores will form within the leaf and spread through the tree canopy. Once the weather becomes dry and the leaves mature, spread of the disease will end. If your tree lost its leaves this spring, it will likely will put on another set of leaves as the weather dries and warms.

Anthracnose can affect ash, birch, black walnut, butternut, buckeye, elm, hornbeam, maple, and oak trees. For ash, maple and oak, the young leaves and shoots are most likely to be infected while mature leaves are mostly resistant. Anthracnose can continue to progress through summer months in walnut and hornbeam trees.

You can reduce stress on your trees and lower the risk of anthracnose in the future by doing a few simple things. Water your tree throughout the growing season and water it well in the fall as it prepares for winter. Wet conditions promote the fungi, so redirect sprinklers that may be splashing on your tree. Only fertilize if a soil test confirms the need. Remove fallen leaves and infected twigs.

Fungicides are rarely necessary for treating anthracnose. If your tree is badly infected for years in a row, then the use of a fungicide can be discussed. If you are looking to plant a new tree, there are anthracnose–resistant varieties available on the market.

Information from this article was compiled in part by Rebecca Koetter and Michelle Grabowski, Extension Educator. For more information on anthracnose in shade trees please contact your local Extension Educator. Stearns, Benton and Morrison County residents can call Katie Drewitz, Horticulture, Small Farms and Local Foods Extension Educator, at (320) 255-6169 ext. 1.