Issue: October 14, 2006
Aphids in globe willow tree
Question:
We have a globe willow in our back yard. It was planted about six months ago. When we bought it, it was in a 5-gallon can. It has been attracting bees, wasps, flies and ants. The tree is full of them, and now we noticed that there are a bunch of tiny black things on the leaves. What are they? We can't even sit in the back yard with all the wasps and bees flying around the tree. Any advice will be appreciated. Thank you.
- Ray. G.
Answer:
You have aphids in your globe willow tree. Aphids are small insects that feed by sucking the sap from leaves (or tender stems). They excrete a syrupy substance called honeydew as a by-product of their feeding. You have probably noticed a silvery sheen on the leaves of your globe willow tree and perhaps on the ground under your tree. This is caused by the honeydew.Ê
Honeydew is attractive to ants, wasps, flies, and other insects that eat the honeydew. There are also insects (including the wasps) that eat the aphids themselves. That is the reason you have so many insects in your back yard. The solution is to eliminate the honeydew that attracts the insects. This means washing the honeydew from surfaces and reducing the aphid population. Treatment to kill wasps and bees will not be effective. Besides, these are beneficial insects that you should not kill.
The aphids can be washed from the tree with a strong stream of water. This also washes the honeydew from the leaf and stem surfaces. You will not remove all the honeydew, but this should reduce the problem.
As you wash the aphids from the leaves, they will fall to the ground. The aphids will try to return to the leaves to continue feeding, but many will fail in their effort to climb up the tree. Some will be eaten by the natural predators of aphids (wasps, syrphid flies, lady bird beetles, and others). Some aphids may become diseased, and others may starve before reaching the leaves. Some may survive to reinfest your tree. You may need to repeat the washing process in a week or two. However, since this is the end of the growing season, there may not be sufficient time for the aphids to successfully reinfest and cause damage this year. They will probably reappear next year, and you can begin the washing process at that time. Start treating early - don't wait for the infestation to become extensive. By avoiding insecticides to manage this problem, you will permit the development of healthy populations of the predator insects that will help keep aphid infestations to a less damaging level.
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.
For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.
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