Hi, some of the aspen trees in my yard have begun to weep a reddish brown sap. I have included 2 pics for dz ID. I am wondering about cytospora canker but it looks somewhat different than the images I have seen online. My questions are these: what is it, will it spread to my other aspens, and how do I control/kill it. Thanks!
Mesa County Colorado trees and shrubs
Yes this is cytospora canker and there is no cure. This ooze is it actually reproducing and sending out spore. You could try cutting it out with a pen knife, treat your knife and possibly the wound with Lysol and try to keep the tree as healthy otherwise by having the right amount of water etc... It looks like I see an irrigation head? right behind the trunk. Tree trunks do not like to be wet and could be a source of spreading the disease and stressing the tree. I am enclosing a document on cytospora and one on healthy roots. http://extension.colostate.edu/topic-areas/yard-garden/cytospora-canker-2-937/
If you live in the Valley, aspens struggle with our heat and soils. They are short lived here. Let me know if you have further questions