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Pest Control With Horticultural Oil

Q: We bought a house several years ago with a huge, full-grown elm tree in the yard. It has aphids, I believe (little hard bumps on the leaves). We have heard of using a ring of Horticultural Oil around the tree, but need more information. How far up the tree? How wide a swath? How often? What time of year? Does anyone have a little more information for us?

Thank you,
Hardiness Zone: 5a

Cee from Roscoe, Illinois

A: Cee,

Without seeing your leaves it's hard to know exactly what kind of insect you're dealing with, but from what you describe it doesn't sound like aphids. If the little hard bumps on your leaves are red or green they are insect leaf galls. Once they appear there is no way to treat them. The good news is, they won't cause any serious damage to your tree-other than being unsightly. If the nodes are hard and waxy looking, you may be dealing with scale.

In regards to Aphids, Wholly Aphids are common to Elms, but they are soft-bodied and their eggs usually spend winter in cracks or crevices in the bark. Aphid infestation on Elms is typically characterized by curling leaves and the appearance of sticky sap in the spring and early summer while the aphids feed on the leaves.

Before you take any action you need to determine exactly what you're dealing with, and whether or not your tree requires treatment. Take a few leaves or a picture of a few leaves to a local nursery or tree expert to diagnose the problem. Good luck!

About The Author:
Ellen Brown is our Green Living and Gardening Expert. Click here to ask Ellen a question! Ellen Brown is an environmental writer and photographer and the owner of Sustainable Media, an environmental media company that specializes in helping businesses and organizations promote eco-friendly products and services. Contact her on the web at http://www.sustainable-media.com

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