What Causes Galls?

Apr 26, 2018

Credit SC Public Radio

Hello Gardeners, I’m Amanda McNulty with Clemson Extension and Making It Grow. A recent caller to the show was concerned about his neighbor’s live oak trees. The leaves were yellowing and they were worried about some shaggy growths appearing on the bark.  Fortunately, Tony Melton interpreted the growths as a common gall that appears on some live oak individuals.

Many galls are caused by insects, such as tiny wasps and midges, that lay eggs on twigs or buds just as they’re beginning active growth. That leads to  interactions between  hormones the plant manufacturers  and growth regulating compounds produced by the insect resulting in a often peculiar growth that  surround the developing insect.  Not only does the abnormal tissue protect the immature insect but the protein-rich inner wall of the gall serves as its food.    Most galls are harmless to the host and can be fascinating examples of the interactions between plants and insects.