All About Maple Tar Spot, the Black Spots on Your Maple Trees

tar spots on maple tree leaves

I recently was conducting some training classes with the Field Service Professionals in Mequon, WI and I saw a tree disease that seems to be increasing in frequency over the last couple of years – Maple Tar Spot. The black spots on Maples are very distinct in their shape and color, but pose no real danger to the trees the disease infects, except for the loss of aesthetic appeal.

Besides showing on several species of Maples, Tar Spot can also develop on Boxelder trees and even Willows. Tar Spot is an accurate name as the disease eventually forms black spots that are roughly ¾ of an inch in diameter. Tar Spot disease on Maples or other species initially starts as small yellowing spots in the early summer and gradually enlarge and turn black. The spots become raised and look exactly like blobs of tar.

tar spot on sycamore tree

How Does Tar Spot Form, and How Can I Reduce It?

There are several fungi that cause Tar Spot. These fungi overwinter in leaf litter and produce spores that will re-infect the tree. There isn’t a need to apply a fungicide as the disease does not affect the health of the tree. Granted, the spots are somewhat disconcerting, but it is only on a cosmetic level. One of the best ways to reduce the amount of Tar Spot, is to pick up the infected leaves that fall around the base of the tree. Those leaves can be burned, buried or even composted. The disease may not be totally eliminated next year, but the amount of activity should be greatly reduced.

For proper diagnosis of any tree disease, always consult a professional tree care specialist. Spring-Green offers a number of tree and shrub care programs, such as root feeding and specialty insect-fighting injections. Find your local Spring-Green today.