Anthracnose Appearing on Maple Leaves in Southwest Missouri but Can Impact Other Trees Too

Contact: Jill Scheidt, agronomy specialist
Tel: (417) 682-3579
E-mail: scheidtjk@missouri.edu

LAMAR, Mo. – Southwest Missouri homeowners have been calling county extension centers in the area with a common question: “What is causing the strange spots on the leaves of my maple tree?”

Jill Scheidt, agronomy specialist with Barton County University of Missouri Extension, provides the answer.

“This year we have experienced a cool, wet spring. These weather conditions are favorable for the development of anthracnose on maple trees,” said Scheidt.

Anthracnose of maples is a fungal disease causing irregular spots on leaves. Anthracnose fungi typically create spots that form around the leaf veins, causing the death of the vein and the surrounding tissue.

Over time these areas tend to fall out, giving the leaves a very ragged appearance. Leaf margins, interveinal areas and some petioles can also be infected, causing malformed and blighted leaves.

Anthracnose can also affect ash, birch, elm, hickory, linden, sycamore, tulip tree, walnut and white oak trees in Missouri.

“Anthracnose can be treated with a fungicide, but is not generally recommended because trees are usually able to recover without long term damage,” said Scheidt.

Trees damaged by anthracnose usually recover by mid-June (when weather conditions are drier and warmer). Raking leaves in the fall and discarding of them is the easiest and best way to control anthracnose.

There are several things homeowners can do to help manage anthracnose.

First, it is important to know that spores of anthracnose fungi over winter in leaf litter and on dead branches. Raking to remove infected leaves in the fall and pruning dead branches will reduce the inoculum available to create infections for next season.

Second, it is a good idea to promote air circulation by thinning excessive twig and branch growth. This will reduce the period of time that leaves are wet and vulnerable to inoculation.

Third, keep trees growing vigorously by supplying one inch of water weekly during dry periods and fertilize in early spring.

Fourth, fungicides are available to control this disease on many hosts. However, fungicides are most appropriate and economical for younger, newly transplanted trees that may not be able to withstand defoliation.

“To be effective fungicidal sprays must begin at bud break before symptoms are noted and be continued at intervals specified by the label (usually 10 to 14 days) through the period of spring rains. Spraying after infection is present will provide little benefit,” said Scheidt.

For more information, contact the nearest county extension center or go online to http://extension.missouri.edu.