DES MOINES - If your oak tree seems to be losing its leaves early, it may be due to a disease called Bur Oak Blight, caused by a fungus. This disease has been seen mostly in bur oak trees, but symptoms have also been found on swamp white oaks.
Leaves on affected trees start to brown between late July and early August, causing the leaves to fall or hang dead on the tree over the winter. Once a tree begins to show symptoms of this condition, it will continue to get worse each year.
Trees affected by Bur Oak Blight have experienced branches dying, and in some cases, entire trees have died. It’s unknown whether Bur Oak Blight is the sole cause of tree death, or if it makes the oak more susceptible to other diseases or organisms.
Currently, there are limited ways to manage this disease. Bur Oak Blight often survives on dead leaves that hang on trees through the winter, so removing the leaves on the ground does not seem to minimize the impact of the fungus. Fungicide treatments have shown some promise, but this method is only recommended once a tree shows symptoms of the disease and not as a preventative treatment.
If you suspect a tree is suffering from Bur Oak Blight, get the problem correctly diagnosed before any management decisions are made. You can send samples to the Iowa State University Plant Diagnostic Clinic for testing.
Tree diseases targeting specific species is an important reason to have a diversity of trees in your yard or forested area. Diversity in your landscape can often reduce the overall impacts of species-specific diseases and insect problems. To explore options for what to plant in your yard, check out the DNR’s Rethinking Maple publication.