Powdery mildew is a common foliar disease of many tree species. The powdery mildew appears as a white growth on the upper surface of the leaves. The powdery appearance comes from a mass of spores of the fungus covering the leaf surface. These spores are able to spread in air currents and cause new infections. The disease is most severe under dry climatic conditions, however high relative humidity is necessary for establishing new infections. The fungus overwinters on fallen infected leaves and on buds of trees.
For more information about Powdery Mildew go to http://http://www.toronto.ca/trees/pdfs/factsheets/Powdery_Mildew_fs.pdf
Tar spot is a fungal leaf disease that may occur on several plants, but it is most common on maple. Tar spot is most common on Silver and Norway maples though it also may affect Sugar, Red and Sycamore maples. The first symptoms of infection show up in early summer as small yellow spots on leaves. The spots become larger and darker and by late August they look like spots of tar. Tar spot does not cause serious damage to established trees. The disease may cause premature leaf drop, but it does not cause permanent damage to the tree.
For more information Tar Spot go to http://http://www.toronto.ca/trees/pdfs/factsheets/Tar_Spot_fs.pdf
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