7/2/2023 0 Comments Norway maple leavesNote that ‘Crimson King’ and ‘Schwedleri’, two varieties with dark purple foliage, are the two cultivars considered to be the most susceptible to this disease, so other readers might want to avoid them when choosing trees to plant in their gardens. Thus Norway maple strain of powdery mildew (a specific clone of Sawadaea bicornis) will only affect other Norway maples. Composting too will destroy most spores.Īlso, there is no need to fear that this disease will spread to other plants: there are hundreds of strains of powdery mildew caused by different fungi, but most, such as the one that affects your maple, are very host-specific. Moreover, shredding the leaves will destroy many of the spores and most of others will die when the chopped leaves decompose as just they do in contact with the soil. Since powdery mildew is carried by the wind and is already present in city plantings all around you, you’ll find no particular advantage to destroying affected leaves rather than using them as mulch. You’ll find the incidence of the disease varies from year to year and is most prevalent when the soil is dry at the end of the growing season, but the air is still very humid.ĭestroy the Leaves or Not? Powdery mildew on ‘Crimson King’ maple leaves. The only logical “cure” would be to remove the tree and to replace it with a variety not subject to powdery mildew. If this disease really disturbs you, the only treatment would be to spray regularly all summer with fungicides, not something easy to do with trees because of their height. Powdery mildew is generally considered an essentially aesthetic disease and does no harm to your tree’s health. Plus it’s already present pretty much everywhere Norway maples are grown. You’ll probably have to get used to the appearance of white powder on your maple’s leaves in late summer, as the disease is wind-borne and thus very difficult to prevent. It’s believed that the fungus Sawadaea bicornis, common on this species in its native Europe, was accidentally introduced into North America and has now spread to much of the continent. Until recently, Norway maples in North America were free of this disease, but over the last ten years or so, it has become very common. Your maple appears to be suffering from powdery mildew. rubra), because the latter is not subject to this kind of fungus. Since I like to shred fall leaves and use them as mulch, is it all right to do so with these diseased leaves or would it be better to destroy the infected leaves to prevent this fungus from spreading to other plants and also from infecting the leaves of our maple in the years to come? Is there anything to do to get rid of this annoying fungus?Īnswer: First of all, I think your maple is more likely a red-leaved variety of Norway maple ( Acer platanoides), possibly ‘Crimson King’, rather than the tree known commonly as red maple ( A. Question: I have a large red maple that, over the last few years, has started developing some sort of white fungus on its leaves. Continue to compost knowing you are being helpful.Norway maple leaves suffering from powdery mildew. And you are helping a natural process to move a bit more quickly. You are being a concerned and conscientious gardener, but be assured that your practices are causing no harm. Then we learned that the virus is airborne and no protection or treatment would make a difference, and that the virus seemed to attack only the one species of maple. For a time, gardening advice articles recommended separating these affected leaves, but that is a tedious task. Norway maples can be subject to a black spot virus. So, while not adding to fertility of the soil, oak leaves add texture and mulch to protect bare soil. The waxy texture of the leaves comes from the lignin, a substance that causes interaction with nitrogen in the soil to leach and bind in the soil rather than feeding the roots. The leaves are acidic, but are a useful ingredient in making leaf mold. One of the highlights of Norway maple tree care is managing the samaras, or seed fruits. These trees, if carefully managed, can quickly become attractive focal points of the shade garden. While it is true that they take a long time, shredding oak leaves produces useful mulch. Norway maple has good resistance to storm and ice damage and has a vigorous growth rate. (Who kept track?!) For this reason, many gardeners prefer to dispose of oak leaves through the municipal yard waste program. There is a saying that oak leaves take 10 years to break down.
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