"Why does my beautiful maple have ugly black spots on its leaves?""Why is my American sycamore bare this year?"
To answer these questions, we need to go back to a chilly, wet evening 5 weeks ago. On May 5th, the temperature dropped overnight to 41 degrees just after an early morning shower that day. We continued this cool, wet trend for 10 lousy days, and though humans (and their trees) may have found the weather disagreeable, anthracnose fungus was celebrating Cinco de Mayo!
Anthracnose fungus attacks newly emerging leaves in the spring when the weather is just right for disease development. The symptoms vary from host to host, but typically infected leaves will have irregular dark spots along veins. Eventually, the leaf will curl, die, and fall. In the case of the sycamore, often the leaf buds are killed before they have even had a chance to emerge.
[Sugar Maple leaf before and after anthracnose fungus]
Anthracnose fungus affects many deciduous trees and seems to be most noticeable this year on sycamore and maple in our area. I have had at least 10 customers per week concerned that their beloved trees were dying due to this fungus. I have also been driving by my favorite American sycamores around my home, only to find them very sparsely leafed and struggling. This includes Upper Arlington's oldest tree, an amazing 3 stemmed beauty that our team pruned a few months ago.
[American Sycamore leaves with anthracnose fungus]Thankfully, I have wonderful news for the stewards of these afflicted trees. Anthracnose is a cosmetic disease for the majority of trees! If the tree is otherwise healthy and well established, it will be just fine. It will replace those lost leaves in July when conditions no longer favor anthracnose development.
How can you help trees with this seasonal infection?
Water your trees during our hot, dry summers! Concentrate the water at the ground level only, do not splash the leaves. All trees will appreciate the extra water, but those that have lost their leaves and are attempting to replace them will relish it! ARTICLE: HOW TO WATER YOUR TREES
Prune your trees for better air circulation and light penetration. This will help the leaves dry faster and it will be harder for the fungus to spread.
Dispose of affected leaves so that the spores are not hanging around next year to re-infect your tree.
Consider fertilizing your trees in the spring so that they have the needed nutrients to stay healthy (and possibly put on 2 sets of leaves if it is another good year for anthracnose infection).
Above all, do not panic! We cannot control the weather or the fungus. Just concentrate on overall tree health and by mid-summer, the trees will have recovered and this disease will be just a bad memory.
Krista Harris | Regional Manager, Russell Tree Experts
Krista grew up in the central Ohio area and became an ISA certified arborist in 2017. She graduated from The Ohio State University with a Bachelor of Science in Crop Science and a minor in Plant Pathology in 2000 and has been in the green industry ever since. Her favorite trees are the American sycamore, American beech, and giant sequoia. [BS in Horticulture Crop Science, The Ohio State University / ISA Certified Arborist® OH-6699A / ODA Comm. Pesticide Lic. #148078]