Maple leaf blister and anthracnose: Two foliar diseases that can appear on same tree
Learn more about the symptoms of maple leaf blister and maple anthracnose, two foliar diseases of maple trees that can appear in late spring on the same tree.
Anthracnose can be a fairly common spring disease on maple leaves in some years. There are several different fungi that cause anthracnose. One of the fungi (Kabatiella) causes newly developing leaves to shrivel and turn black, while older leaves develop dark brown lesions along the leaf veins. A different fungus (Discula) produces lesions that are tan to reddish-brown and are centered on and immediately around the veins.
In general, cool, wet weather produces worse anthracnose than warmer, drier weather. Severely affected leaves fall off. Infections caused by anthracnose usually affect the lower branches and branches in the interior of the tree more than the upper part of the crown. Generally, a new set of leaves grows to replace those that fell off. There isn’t much to be done for treatment because infection has already taken place before the symptoms appear.
Maple leaf blister can occur on red and silver maples. From information I reviewed to write this article, I got the impression it is an uncommon disease in Michigan. This 2016 spring was the first time I have ever seen it. People would probably be much more familiar with another species of Taphrina that produces the dramatic and colorful symptoms of peach leaf curl.
Although maple leaf blister looks somewhat similar to maple anthracnose, there are some differences. Several different species of Taphrina can cause leaf blister of maple. Compared with maple anthracnose, the spots are more rounded in shape, don’t follow the veins and contain small, raised blisters. Lesions are a mix of lighter brown to black. The fungus overwinters in bud scales and attacks developing leaves early in spring. With the right weather conditions, the infection can spread rapidly and cover most of the leaves in the canopy, not just the lower canopy. Once the leaves harden off and the weather becomes warmer and drier, the infection cycle stops.
To make things interesting, anthracnose and leaf blister can occur on a tree at the same time. The only way to be certain if a tree has one or the other or both is to send samples to a diagnostic services laboratory, such as Michigan State University Diagnostic Services, and have it confirmed.
Regardless of which disease (or both) is causing the symptoms, there aren’t any fungicide treatments that are effective – the infections took place much earlier in the season. So what can you do? A light application of fertilizer to provide readily-available nutrients and making sure the tree has adequate water during periods of drought over summer will help trees recover from the stress of putting out a new set of leaves. MSU Extension also suggests raking up and discarding fallen leaves, but many of the fungi that cause diseases overwinter on twigs and bud scales.