marssonina leaf blight in trembling aspen
I have several aspen in my Woodbury back yard. Two of them have been hard hit by marssonina leaf blight this year after another bad year in 2015. The 2015 episode led to die-off of some lower limbs, which were removed. It looks as though the 2017 aftermath will be similar. Things I've read state that it usually does not kill the tree, but I'm becoming concerned. I understand that fungicide spray can be applied in the spring, but I know my wife would be concerned about possible health effects on dogs, which routinely utilize the yard. Four other aspen. possibly clones of one which died and was removed in 2008, seem to be resistant and are not much affected. Have you any advice for me. Robert Callery
If you haven't done so already, consider asking a forester or certified arborist to assess the trees' health onsite and recommend a course of action. Fungicides may or may not be needed, but if they are, the consultant can explain which is best and how the products might affect other life forms. The consultant should also have the equipment needed to apply the product correctly.
As you have noted, some aspens are more disease resistant than others. However, if those that are doing well in your yard are a part of the same clone as those that have died, they are genetically identical and equally susceptible. Other factors may account for their leaves being less affected.
You may already have read about non-chemical ways to control the disease but following is a good summary: