Answer: There are many factors which could be affecting your maple. Diseases such as verticillium wilt can cause the dieback you describe, as can insect pests like borers and maple worms. Environmental factors, such as drought or wet feet -- saturated soil -- as well as road salt can also cause dieback. Maples don't like to have the soil around their roots compacted, so avoid driving over the area under the tree. Your maple may also have a nutrient deficiency. Try pruning out dead wood, sterilizing cutting tools between cuts with rubbing alcohol. Inspect leaves for insects, and apply a thick layer of compost as a mulch to help provide nutrients. Moss on tree trunks merely indicates a moist, shady environment; it will not harm the tree.
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