Question: Does anyone else have as many problems with aspen trees as I do? I thought they were easy to grow when I planted several in my yard 10 years ago. They get aphids almost every year, which drip sticky residue on my car. I treat for scale insects repeatedly. Now there are borers in several trees. The leaves get black spots, turn yellow and fall off. But the worst problem is the sprouts which come up in my beds and in my lawn. They seem to get worse every year. Should I just remove the trees and plant something else, or are there better ways to handle these problems?
Answer: Aspens are a unique tree. When we see beautiful groves of them growing wild in the mountains, we seldom look closely to observe the insects and diseases which are right there with them. They have underground rhizomes, or stems, which send up new sprouts to replace the ones which are killed by insects and disease and eaten by deer and other grazing animals. Even if you remove all the trees, they will continue to send up sprouts from those underground stems.
Aspen leaf spot can be largely controlled by cleaning up all leaves in the fall and making two applications of fungicide in the spring just as new leaves are emerging. The fallen leaves provide the spores which infect the new leaves.
Several fungicides are effective, including some natural or organic ones. Lime sulfur (calcium polysulfide) is my favorite.
Ladybugs will usually control aphids, but it may take two or three weeks. Aphids are easily controlled by several different insecticides. I use Neem oil, which is a safe organic. Scale insects and borers are harder to control because they are protected from sprays. However, several systemic pesticides are available which are translocated by the tree’s circulation system to reach the pests. Systemic pesticides are applied to the soil and taken up by the roots, sprayed on the leaves or injected into the trunk. Spinosad is a systemic organic insecticide. Check with local full-service nurseries for other pesticides.
I lived in a home with numerous aspen trees. I soon discovered that I needed to let a few of the sprouts grow into trees to replace the ones which were dying. I removed the sick trees before they were completely dead. I discovered that lawn weed killer worked on the sprouts without apparent damage to the established trees. I sprayed them twice a year wherever I could avoid ornamental plants. I applied weed killer with a paintbrush where ornamental plants were too close.
For those readers who are considering planting aspen trees, I suggest birch trees as a substitute. They have the same attractive white bark, but many fewer problems.