Fact Sheets no. Five fungi cause most foliage diseases on aspen, cottonwoods and other poplar species. Foliage diseases develop readily in wet, cool weather. Foliage diseases decrease a tree's aesthetic value and can cause premature defoliation.
Severe outbreaks can affect the general health of the tree.
To reduce future disease problems, rake up and dispose of leaves and prune out branches with cankers. Timely fungicide application can prevent severe outbreaks. Foliage diseases can reduce the aesthetic value of aspen and cottonwood. Occasionally, a severe disease outbreak causes premature defoliation or dieback of parts of the tree. If a tree loses its leaves early in the season, it may grow new ones and its health is not seriously affected.