Anthracnose is a fancy term for certain leaf spot or leaf blight diseases. Cool and wet spring conditions favor the fungi that cause anthracnose. Oak anthracnose has been common this spring. Browning of the leaf tissue occurs, especially along the margins of the leaves and also along the veins of the leaves. When severe, much of affected leaves can appear papery brown and leaves may fall from the tree.
There are many different, but closely related anthracnose fungi. Each fungus is specific to a particular host plant. For example, the fungus that causes anthracnose of oak does not infect ash trees. All anthracnose fungi require water to infect a tree.
Fortunately, established trees can typically withstand infection by anthracnose fungi and are able to recover as the growing season progresses. The warm and dry conditions of summer do not favor disease development.
Anthracnose of shade trees can be managed by using a combination of approaches.
- As feasible, rake and remove fallen leaves to help reduce overwintering of the fungus.
- Prune trees as necessary to promote good air flow throughout the canopy of leaves. Plant trees so they will receive good air circulation.
- Improve overall vigor by mulching with an organic mulch such as wood chips and watering when conditions are dry.
- Protectant fungicide sprays are an option, but are seldom warranted.