We are having trouble with 2 aspen trees in our yard. We live in the foothills at about 7500 feet on a northeast facing slope. The conditions appear to be ideal for aspen because we have a number of other healthy aspen trees that are flourishing on our property. The problem with the 2 trees I'm inquiring about is that they both develop browning of the edges of the leaves in June/July. I've attached a picture of what the leaves look like now. The browning spreads over the leaves turning the whole leaf brown and dry by the end of August never allowing the leaves to turn yellow in fall like the other aspen trees. In addition to the browning, the brown areas have dark brown/black spots that are yellow in the center. I've also noticed that these 2 trees are the only trees that don't send out suckers from their roots. They are medium/large fairly well established trees, approximately 10 years old. Do you have any suggestions for what we can do to improve the health and appearance of these trees? Thank you.