Gall wasps prey upon oak trees

We moved last year and we have a new place with more trees! Trees are an important feature for us. Our new location has two and a half acres. We have five maples and 12 red oaks! We enjoy walking among the trees. We delight in their changes through the seasons, from the smallest buds breaking in the spring to bring on the lime green initial leaf color to the vibrant fall colors this time of year. Even enjoying the textures of different bark and identifying trees in winter is enjoyable.

We are always assessing tree health and looking for new things happening to our trees. We are intrigued sometimes by early leaf drop, disease issues and enjoy finding insects on and around their trees. Nature is truly inspiring and intriguing!

Trees can be messy, but that comes with the territory. Walking back from feeding my koi the other night, my husband Bill found an interesting thing on the ground. Amid the quarter-sized acorns dispersed all over was a quarter-sized round red ball with mottling. He asked me what it was, but I didn’t know off the top of my head. I had a general idea that it was due to an insect, so I began investigating.

Oaks are preyed upon by gall wasps (family Cynipidae) that come early in the spring and lay an egg on the buds before leaves form. When the larva hatches it feeds on the leaf tissue and secretes chemicals that modify the plant tissue into a gall (round shape). An amazing thing of nature.

The gall we found was the Acorn Plum Gall, caused by the wasp Cynipid Amphibolips quercusjuglans. It does have red hues like a plum, with speckles that increase as it dries out. It grows with an acorn on the trees. These galls can be 1/2 inch to 2 inches in diameter, and they look like large spheres. There are over 750 kinds of galls on oaks that can form on leaves, twigs and branches, and the shape can tell what kind of wasp preyed on it. Most are not harmful, but a few on the branches can be harmful and can kill a tree in extreme circumstances.

So now along with acorns and branches that fall during rains, we can watch for the galls. Check out your oak trees and see what unusual galls you find — it’s a great activity for all.

To learn more about the acorn plum gall and other interesting galls on oaks, go to http://go.osu.edu/acronplumgall

Hughes is an Ohio State University Mahoning County Extension Master Gardener volunteer and certified Volunteer Naturalist.


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