News release: Anthracnose of Trees

Tim Baker, MU Extension Horticulture Specialist
102 N. Main, Suite 1, Gallatin, MO 64640

Release Date: June 11, 2015

Headline: Anthracnose of Trees

This year, I am seeing a lot on anthracnose on maple and especially sycamore trees.  Every year differs in the occurrence and intensity of this disease, but with the cool, wet weather we have been experiencing this year, anthracnose seems to be taking off.

“Anthracnose” is a generic term which refers to diseases which are caused by fungi that produce similar symptoms on leaves.  These organisms are species specific.  In other words, the fungus that causes maple anthracnose is different than the one that causes sycamore anthracnose or anthracnose on your green beans.

Anthracnose usually appears as dead areas on the leaves, ranging from a few spots to blotches that involve most of the leaf. The spots are usually brown, but can range from a reddish tint to black.  The leaves often become twisted and distorted as well.

While anthracnose is caused by a fungus, and theoretically a fungicide could be used to treat it, we generally do not recommend chemical control.  Although the trees are stressed, they usually recover without long-term damage.  New leaves should be symptom-free as soon as it warms up and dries off.  Older leaves become more resistant to the disease, and less likely to support new outgrowths of the fungus.

The disease certainly looks serious, which alarms the homeowner.  Fortunately, it is not, unless it is on smaller, newly-established trees. Newly-planted trees may suffer serious problems from an anthracnose infection.  In this case, you might consider using a fungicide spray.

To control anthracnose, be sure to rake up all the leaves in the fall, and discard them.  If you leave them around, the fungal organism will overwinter in the leaves, and will be around next year to infect your tree again, if the conditions are right.

It may also help to fertilize your tree.  This helps invigorate the tree, and vigorously growing trees are more resistant to infection.  Be sure to fertilize during the spring, not the fall.

In general, do everything you can to reduce stress on the tree.  Stress is cumulative, and stressed trees are more prone to disease.  In addition to fertilizer, be sure to water the tree during drought.  Mulch will help reduce water needs, but keep it away from the trunk, if possible.

Anthracnose is known to affect ash, birch, elm, hickory, maple, oak, sycamore, and walnut trees.

We have a guide on anthracnose on shade trees.  Give me a call at 660-663-3232, and I will be happy to send you a copy.