This summer, we have received a lot of calls from clients asking us what the yellow and/or black spots on the maple tree leaves mean for the tree’s health. Because of all of these enquires, we decided to make this blog post explaining what these spots mean, and what you can do to prevent them.
Understanding the Problem
The appearance of yellow and black spots on maple leaves is often due to a fungal disease known as tar spot, primarily caused by fungi from the Rhytisma genus.
Below is a series of pictures by James & Griffin Dill showing the progression of tar spots on a maple tree. If your tree is afflicted with tar spot disease, you will typically begin to see yellow spots on the leaves in June. By August or September, these yellow spots will have turned black.
Image source: James & Griffin Dill, University of Maine Cooperative Extension
While tar spots may seem alarming, research shows they do not pose a threat to your tree’s health. However, if you find them unsightly and wish to prevent their occurrence in the next season, you can rake and dispose of the infected leaves in the fall. This helps to reduce the number of fungal spores that can reinfect your tree in the spring. Keep in mind, though, that this strategy is only effective if your neighbors also manage their infected leaves and avoid using them as compost or mulch. Otherwise, spores from their trees can spread to your yard, continuing the cycle of infection.
It is important to note that there are no fungicides registered to combat tar spots in Canada.
For more information about tar spots, visit the following links:
Conclusion
We hope you found this blog post informative. If you’re in Kitchener, Waterloo, or Cambridge and need a consultation regarding your tree concerns, please contact GreenCare Tree Services. Our experienced arborists are ready to provide top-quality tree services tailored to your needs.