Treating Aspen Mites
I've got an aspen that has got what look to be little mites all over it. I've been negligent about treating it, and now the trunk is starting to split and weep. Is there a way to kill the mites and save the tree? Also, if I have to cut it down, what precautions can I take to keep the mites from moving to my other aspens? (The nearest ones are 10 feet or more away and show no signs of being affected so far.) Thanks!
Denver County Colorado aspen
It looks like those may be the crawler stage of Oystershell scale, although I can't say definitively because I can't see an individual insect with enough detail to identify it; when I try to enlarge your photo, it goes all pixelated.
There is a brief period between egg hatch and colonization when the crawlers move around looking for a feeding site. Some of them could be carried by wind or on the body of an animal to your other trees but usually the crawlers either find a feeding site or perish.
Chemical treatments are applied to coincide with egg hatch and you may have missed that window. You can try treating your tree with a dormant season horticultural oil but that will be less effective once the insect is protected under its covering.
Cracking can be a result of scale feeding and the disease Cytospora can invade damaged limbs. Since you say you see "weeping" and cracking on your tree, we recommend you get an arborist out to evaluate your trees and recommend a management strategy.
Here is some information from the Forestry Service about these insects:https://sdda.sd.gov/legacydocs/Forestry/publications/PDF/41.Oystershell%20scale%20FINAL.pdf