Tar Spot on Maples

Asked September 22, 2019, 8:06 AM EDT


Would applying a fungicide to the ground, after fall clean up and again in the spring before the leaves come out, kill the mold spores that winter over? Our plan is to try to clean up all the leaves but it will be impossible with the number of trees and acreage. If the leaves are mulched by the mower does that just spread the spores even more?

Wood County Ohio

1 Response

For most maples and other susceptible trees and shrubs, tar spot is not a serious disease, but primarily is a cosmetic disease that makes trees and shrubs look unsightly. Tar spot does not kill trees or shrubs, nor does it typically even cause serious defoliation. The following links will provide more information on tar spot: https://www.mortonarb.org/trees-plants/tree-and-plant-advice/help-diseases/tar-spot-maple-rhytisma-pp and https://hort.extension.wisc.edu/articles/tar-spot/ .

Raking and destroying leaves will reduce the number of spores that survive to the next spring. Ideally, for this to be truly effective, everyone with an infected maple in the neighborhood should rake and destroy the leaves of their tree. Composting may not completely destroy spores, because home compost piles seldom heat up enough to really kill fungal spores.