Aspen are becoming thin

Asked August 15, 2018, 11:52 AM EDT

Is there a way to identify a disease or pest that is killing our aspen trees? Established trees have wilting leaves just on one branch at a time, then the branch dies. They are getting supplemental water with a sprinkler system, so I don’t think it’s a watering problem.

Custer County Colorado trees and shrubs

3 Responses

This is likely a disease called Marssonina leaf spot. I have seen this periodically in Salida, perhaps a bit worse this fall than we have seen in the past few years. It will likely cause premature leaf drop this fall, and boring fall color. Best prevention you can do for future is to clean up fallen leaves and discard them (spores survive composting process at our altitude and can reinfect trees next year).

More information is available at It also offers suggestions for management of this and other common diseases of aspen. This likely will not kill your tree as it is so episodic (bad years and good years).

I hope this is helpful!

Thank you Kurt! Would it help to apply a fungicide in the spring? If so, what would you recommend?

No. Cleaning up the leaves breaks up the cycle adequately. Most of the severity of these outbreaks is weather -dependent...this has been a bad year for this disease. I suspect that the fall colors in the high country will also be subdued this year as well.