Question
Hello

I have a grove of Aspen trees in my backyard............Hillsboro, OR.

The leaves have developed brown spots on them and are curling a bit....also a sticky sap like substance is on the trees. Could it be due to not enough water?  he trees are 14 years old and about 3 4 stories high.

Answer
Sounds like aphids. These small insects suck the plant juices form the leaves and small twigs and cause the leaves to curl. They secrete a substance called honeydew which is high in sugar content and sticky. Control the aphids and the sticky will go away. Treat the tree with an insecticide called Bayer Advanced Tree and Shrub Insect Control. This is applied to the soil around the tree and the roots will carry it to the leaves and twigs and when the insects suck the plant juices they are killed. It will take a couple of weeks to reach the top of large trees. Here is a web link to this product. Check with your local garden type store or nursery for this product. http://www.bayeradvanced.com/tree-shrub-care/products/12-month-tree-shrub-insect...