Master Gardener: Galls |

Master Gardener: Galls

Vicky Barney
For Steamboat Pilot & Today
Galls on an oak leaf. (Courtesy photo)

As I walked through my garden the other day, I noticed three tiny red balls sitting on top of an oak leaf. They were a beautiful red color. A few days later, I saw a fuzzy red ball attached to a branch of a rose bush.

The balls on both plants reminded me of Christmas ornaments and, I have since learned, were created by plants responding to gall making insects.

Some plants will grow abnormal shapes, called galls, if infected by microorganisms. For example, inconspicuous woody galls on a Juniper tree in my yard a few years back were the result of a fungal infection.

Plants will also create galls in response to chemicals released by certain insects and mites during feeding and egg-laying activities. The pretty galls I saw were likely due to activity by tiny gall wasps in the Cynipidae family.

A mossy rose gall. (Courtesy photo)

There are over 750 species of gall wasps in North America, and they are responsible for nearly all the insect galls found on oak and rose plants. Most produce galls on oak leaves, buds or twigs, and their galls are commonly found on roses bushes as well. Galls come in various shapes and sizes and can be colorful, depending on the life cycle of the inhabitants.

The gall making process is very complex and not completely understood but may go something like this: Using chemicals, a female gall-making wasp instructs a plant to build a space for her eggs. Then, the larvae advances gall formation by exuding more chemicals, telling the plant to expand the space to accommodate more growth.

Other gall wasps may join the original inhabitants and influence the plant to further expand the gall. At some point, the gall wasps mature and fly off, and the empty gall remains behind.

Gardeners need not worry about this kind of gall or gall wasps. Even though the gall making process allows gall wasps to take energy from the host plant, plants are rarely adversely affected.

And while some galls may be unattractive, others are quite interesting looking, especially when they are brightly colored. As for the gall wasp, it is a tiny creature that is a beneficial source of food for wildlife.

Based on my recent walks through the garden, it appears to be a good time to look for colorful galls.

Vicky Barney gardens for wildlife and is a member of the Master Gardener Class of 2011.

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