Fungal Diseases on Aspen Trees

Since aspen trees are a native to central Oregon, most of us have at least one in our landscape. Along with the beautiful white bark and the golden fall color, come several diseases that seem prone to affect the Aspen trees. Some of the disease problems are due to a lack of care by the homeowner. I preach over and over every fall to rake up those fallen leaves. If left on the ground you are more apt to develop Black Spot on your aspen trees.
Black Spot is a fungal disease that causes the Aspen leaf to turn black around the edges and lose leaf mid summer. It most likely will not kill the tree but can be very unsightly in the landscape. Now is a good time to treat your aspen trees, especially if you have had this fungal problem in past. You want to spray your trees with a fungicide just as the bud swells and repeat again as the leaf starts to emerge from the bud.
Another fungal disease is Septoria Leaf Spot. Symptoms are small brown or black mostly circular spots on the leaves. The treatment is the same as for black Spot.
Aspen Galls is another problem on the trees. Not a fungal disease but an insect. The tree will have lumps in the branches. This is caused by a tiny fly like insect that bores into the branch and lays it's eggs. The larvae feeds off of the branch, causing the gall. This gall won't usually kill the tree, but can cause problems, by weakening the branch. I suggest that you cut the gall off of the tree by cutting the branch just behind the gall.
Aspen trees are relatively short-lived, usually 20 to 40 years for individual trees. As they become older they will become more prone to problems such as sooty fungus and rust blight.