Maples tend to develop many different leafspots during the spring and summer, none of which are fatal but can cause extensive leaf drop.
These leafspots are caused by various fungi but infection rates are higher when the trees are in stress. Trees and shrubs under stress conditions are more susceptible to all diseases and also insect attack. Stress can be caused by inadequate watering (especially during high temperatures and dry conditions), root or bark damage, and girdling twine and roots.
Leaf spot diseases can be especially severe after a period of abundant spring rains followed by periods of drought. This is because the immune systems that protect the trees are compromised due to the stress of the two wildly different water situations.
The leaf spots may coalesce and the leaf may begin to crinkle, curl and turn black. The tree may also slough many of these leaves, making it appear the tree is dying. This is usually not the case as the tree is simply ridding itself of diseased leaves that no longer perform the photosynthesis functions.
There is no treatment needed for these diseases but trees that are being adequately fertilized and watered tend to have fewer disease problems including leaf spot. The most important key to reducing stress is PROPER WATERING!
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