Treating Aspen tree problems
Fungicide treatments might be warranted for trees that perennially suffer from fungal diseases, but, unfortunately, that describes most aspens in Denver since aspens are not suited to our soils or elevation. When planted here, they tend to develop problems.
If you want to treat trees with a fungicide, you need to start applications at bud break in the spring, and then repeat applications two or three times during the growing season at 12- to 14-day intervals. Please follow label rates and directions when applying.
Other controls include irrigating in early morning so leaves can dry out, adjusting sprinkler patterns to avoid spraying the foliage, spacing trees to provide air circulation, and fall removal of infected leaves, twigs and branches to reduce the amount of disease next spring.