Hickory leaf gall - Knowledgebase Question

Beverly Hills, Mi
Question by prijnovean
March 13, 2010
I have a 80 year old hickory that has had leaf gall the last three seasons. Each year the leaf loss is worse and the refoliation is less. I know this is a stress on this tree. The only advise I get is to try and keep the tree healthy as possible with proper water and fertilizer. Nothnig seems to be helping. Have any other ideas?

Answer from NGA
March 13, 2010


The galls are caused by aphids and they are generally protected inside the galls. Hickory gall aphid (Phylloxera caryaecaulis) forms galls in June on leaf stems and new shoots. The hollow galls contain the young aphids. In July, aphids reach maturity and leave the galls, which turn black. Some eggs remain over winter in the old galls and in crevices of the bark. A spray of insecticidal soap, just before the buds swell, will help reduce the numbers of pests. If you repeat this treatment several years in a row, you will be able to significantly reduce the population, and the damage to your hickory tree. If the tree is large and valuable you may want to have it sprayed by a certified arborist. They have access to pesticides such as malathion which are more powerful than insecticidal soap. Best wishes with your hickory tree.

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