Maple Tree Pests and Problems
As a former editor of the LoveToKnow.com Garden channel, I frequently get questions on how to identify and deal with common maple tree pests and diseases. Unfortunately, without photos, problems can be hard to identify. I've included a slideshow on this page to help you identify some of these problems, and as I come across good examples of the maple tree pests or problems, I'll photograph and add these to the slide show. Whether you have a problem identifying what a maple tree gall is, or you don't know what lichens look like, you'll find the answers here, as well as the photographs to help you identify them.
Maple Tree Tar Spot
The maple tree tar spot is pretty easy to identify. I've included a photo below to help you see what one looks like. The tar spot is caused by a fungal pathogen in the genus Rhytisma. It affects maple trees, especially the Norway Maple, Silver Maple and Sugar Maple. It will not kill your trees, but it is unsightly and can cause early leaf drop before the fall season.
The spots first appear as small yellow spots in June, then progress to the familiar black spots on the leaves which can be 1/8 inch in diameter to an inch or more on the Norway Maple. The spots can also appear on the seeds (samaras).
The fungus winters-over on leaves that have dropped to the ground. If the leaves are not raked up in the fall, the spores will reappear in the spring on the old leaves and spread to any nearby tree. Treating the trees is usually not effective since the spores can travel from a neighbor's tree onto your trees.
If your tree has these spots, which then turn into curling leaves in mid-July, you may have a different disease, Anthracnose.
Anthracnose is commonly mistaken for tar spot. However, the damage is much more extensive as it affects not only the leaves but the branches as well. The spots on the leaves are many, and are usually much smaller than the 1/8 inch tar spots.
This condition commonly occurs when there are long periods of cold and wet weather. The areas affected may include the dark small spots and irregularly shaped dead and brown areas on leaves. The leaves usually fall off in the early spring, followed by a second set of leaves which will also die off. The branches may develop cankers which can girdle the branches and kill them.
The disease is perpetuated because the fungal spores over-winter in dead leaves. When there is a prolonged wet spring, the spores have a perfect breeding ground. The spores are carried by the wind to other trees. Once infected, the disease can over-winter in the host plant in the infected branches and twigs.
The disease can be controlled by removing dead leaves in the fall from the base of your trees. Fungicide can also be applied, but due to the size and number of trees that may be affected, commercial applications are usually required. You can call your local Cooperative Extension office to find out what fungicides are legal in your state.
Sooty Mold on Trunk
Sooty mold sometimes occurs on maple trees. This mold feeds on the sticky substance (honey dew) left by aphids and scale insects. If the mold rubs off easily on your fingers when you touch it, it is sooty mold. This won't kill your tree and it can be treated easily.
Try using Bayer Advanced Tree and Shrub mix. Follow the instructions carefully and mix it with water. It is applied at the base of the tree and is taken up through the roots. This application should also stop reinfection for up to one year.
Lichens can be found on many maple trees, especially mature trees. Lichens are not harmful to your trees. They don't feed off of your tree- they feed off of air. You don't need to do anything to the lichens since they aren't harmful. If you feel the need to get rid of them anyway, copper fungicides can assist you in this endeavor. As always, read the label and follow instructions to a "T."
One of the worst diseases that your tree can get is verticillium wilt. This affects the vascular system of the tree and usually ends in death of the tree. The verticillium fungus is a soil-borne disease and can live in the soil for years before it makes an appearance. It enters the tree through the roots.
Common symptoms are yellowing leaves, followed by the leaves wilting and entire branches can be affected. In some maples, the entire crown can wilt and die within a short period of time.
Proper diagnosis can help you make the right decision in what to do with your tree. Call your local Cooperative Extension office to see if they can come out and examine your tree. A core sample of the tree will be needed for correct diagnosis. A green or brownish green color can be found in the sapwood of affected trees.
Phytophthora Root Rot can affect maple trees, especially when there is a wet spring or a tree is living in poorly drained soil. The main symptom of this problem is yellow, smaller than normal, leaves. Dark brown and black roots can be found on the tree when root rot occurs.
Plants can't usually be saved when this happens, and they will need to be cut down to avoid injury to people or damage to property.