Leaf galls rarely affect tree health
Q. I have three maple trees. Last year I noticed the leaves in fall were brown in spots with these funny horn-like structures sticking up from the leaves. What do I do to rid these trees of this? Will it kill my tree?
Joan from Canfield
A. Funny little horns coming out of the leaves or little red “sacks” coming out of the leaves are all galls. There are many galls which affect maple trees. In general, they’re harmless. Rarely do they ever cause enough damage to really affect tree health.
Galls are caused by interactions between growing leaves and the chemicals emitted by mites and other insects. These chemicals regulate growth within the leaf, causing the strange structures to appear. Unless you are really taking a look at leaves, you’ll never notice it. We really started to get calls about these at our clinic in mid-August when leaves started dropping prematurely due to our extended dry period.
The mites that caused this damage are long gone. They laid eggs within these galls. When the eggs hatched, the new nymphs had to find new growth to continue their development. Without new growth, these insects don’t have a way to create new galls. Thus, they will seek shelter within the cracks and rough areas of the tree’s bark as well as other protected areas to hang out for the winter.
Though the formations on these leaves can look quite alarming this year, there’s no need to worry and no need to implement control options for the mites. Large trees might have some unsightly sections, but they’ll survive the infestation. Only in rare cases of small trees with heavy infestations is any control warranted. In these cases, control options are best utilized in spring.
In the meantime, enjoy the wonderful shapes and colors of nature’s interaction between trees and insects.
More details on maple galls can be found here: http://go.osu.edu/maplegalls
Eric Barrett is OSU Extension educator for agriculture and natural resources in Mahoning County. Call the office hotline at 330-533-5538 to submit your questions. Clinic hours are Mondays and Thursday from 9 a.m.-noon, through October.