Spots on your maple leaves? This may be due to a fungal condition called anthracnose. As the frequent spring rains coincided with leafing out of maples, some trees are now showing signs of this disease, which thrives in warm, moist environmental conditions.

Anthracnose typically affects young leaf tissue, and is caused by fungal spores that overwinter in leaf litter. Symptoms vary from small, circular to irregular spots that are tan, dark brown, or black, to larger, irregularly shaped blotches of dark brown, dead tissue along the leaf margins and between the veins. As anthracnose lesions are very dark in color, they can be easily confused these with another fungal leaf disease called tar spot. But black tar spot lesions develop during late summer or early fall, rather than appearing on leaves this time of year.

The good news is anthracnose is basically an aesthetic issue and established trees that are otherwise healthy can withstand the infection leaf drop without serious long term affects. With time, an infected tree that has dropped its leaves will re-leaf a new flush of growth from underlying leaf buds that otherwise would have remained dormant.

Keeping leaf litter raked up in the fall is the first defense against maple leaf anthracnose.

Did you know? Anthracnose is a common foliage disease of shade trees in Iowa. Symptoms can also occur on sycamore, ash, oak, walnut, linden, hickory, willows and other deciduous trees.

Horticulture Questions? Contact McCormick at yvonne@iastate.edu for information or advice.