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Common Maple Tree Issues

Source: Sarah Eggert, Meeker County Agricultural Intern & Karen Johnson, Extension Educator- McLeod & Meeker Counties

Have you noticed that your maple tree has been losing its beautiful leaves this summer? Have there been irregular growths on bumps on the leaves? Over the last few weeks, the University of Minnesota Extension has seen several common maple tree issues. The main three that have been popping up this summer are anthracnose, tar spot, and leaf galls.

One of the most common diseases that are showing up in Minnesota is anthracnose. This is a general term that describes different diseases that produce symptoms such as leaf spots, colored blotches, twig cankers, and dieback on many different trees and shrubs. In a majority of cases, anthracnose does not cause any permanent damage to established trees. This disease is best managed by removing the stems that have been damaged and disposing of them immediately. It also helps to remove the stress of the tree by adequate watering. If leaves are falling, rake away the fallen leaves and remove them before the first snowfall to prevent further spreading.

This next disease is easily identifiable when looking closely at the leaves. Tar spot is a disease that is caused by a fungus and gets this name because it appears like droplets of tar on the leaf. In general, tar spot will not harm the long-term health of the tree, but it can be unappealing and in severe cases, cause leaf drop. The best way to control tar spot and other leaf spot issues, is sanitation. You can rake the leaves away and dispose or destroy them as they fall. Removing these leaves away from the base of the tree will prevent further infection next spring. Applying fungicides can also be an option, but is only suggested if the tar spots continue for several years.

If you are still noticing something wrong with your leaves on your maple tree, but doesn’t seem to be tar spot, it might just be a leaf gall. These are created by insect or mite feeding or egg laying activity. They are most commonly found on the leaves but can be found on the stems as well. Galls typically form during the late spring, which is when the main growth stage of the tree is. However, most galls are not noticed until they are fully developed and can remain on plants for an extended period of time. Most galls do not affect the overall tree health, so it is recommended just to leave them to promote plant vitality. Like the other diseases, there are some chemical options that can be taken into consideration, but it is often timely as to when to properly apply the treatment.

While these common issues all have pretty different looks, they all start within the leaf. Keep an eye on your maple trees this season in order to prevent any diseases or other issues from spreading within your yard. Properly maintain care of your trees to further prevent these diseases or deficiencies from starting. For further information on your trees and problems it can suffer from, visit the “What’s Wrong with my Plant?” page on the Extension website at


Karen Johnson
Extension Educator, Ag Production Systems
(320) 484-4303
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