Disease on leaves of Aspens
Can you kindly ID the problem with my Aspens? I have asked 2 arborists and they are not sure what it is. Also if you can advise what to do about it. They don't appear to be an insect, but rather very rigid to the touch. Many leaves are affected on the 7 "groves" that are in my yard. Much appreciated. An image is attached.
Santa Fe County New Mexico
This looks like galls formed by eriophyid mites. As eriophyid mites feed on leaf tissue, a hormone-like toxin is introduced into the leaf. Leaf cells then grow in a distorted gall shape. These galls then provide shelter for the eriophyid mites. Eriophyid mites are very small, perhaps 1/256 inch. Eriophyid mites have only 4 legs rather than the 8 legs of other mites.
There is not a lot you can do to prevent eriophyid mite injury to leaves. Tree health is usually not affected. For these reasons, no control is recommended. You can clip off affected leaves and bag/discard if you wish.
You might take some of the affected aspen leaves to the NMSU - Extension office in Santa Fe County. They may have a microscope that allows you to see these eriophyid mites crawling around and among the leaf galls.
3229 Rodeo Road
Santa Fe, NM 87507
Thank you for your quick reply as well as your interesting insights. Would spraying dormant oil in the Fall or next Spring help prevent these mites?
Yes, possibly. A dormant oil should be applied to the aspen in mid-late winter (Jan-Feb), temperatures are 50 or higher.
For now, suggest you just clip off as many infested leaves as you can reach, bag and discard.
See next to last paragraph of text at
http://www.ext.colostate.edu/pubs/insect/05557.pdf and http://www.ext.colostate.edu/pubs/insect/05569.pdf
Thank you for all your expertise as well as the helpful links!