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Thursday, July 10, 2014
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Published: Wednesday, 11/9/2005

Odd bumps, splotches may be harmless

Halloween may be over, but some plants are still wearing their warty, lumpy, and fuzzy costumes. These shapes - called galls - are abnormal growths on plants that often are caused by insects.

Galls can grow on stems, leaves, flowers, and even roots of plants. Scientists say some can look like table tennis balls, dunce caps, saucers, sea urchins, or other shapes. Some grow quickly and others slowly.

"Oak galls can also be thick swellings on the twigs or leaf stems, round apple-like growths, or fuzzy cotton balls on the leaves," says Amy Stone, Ohio State University extension educator in Toledo. "These growths can be colorful and may be tan, black, brown, red, white, or pink."

They are created by mites, gall midges, or gall wasps. Most of the symptoms start in the spring when the tree is actively growing. Ms. Stone says the female deposits eggs inside the tissue of the leaf or branch. Once the eggs hatch, the larvae irritate the plant in a way that stimulates it to form a callus.

Fuzzy oak gall resembles a tan cotton ball on an oak leaf. Fuzzy oak gall resembles a tan cotton ball on an oak leaf.
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The growths are difficult to prevent, and you may start to see a few more gnarly bumps and bulges on your tree. But the tree won't die from a gall attack. "They can look very unsightly, but do not affect the long-term health of the tree," Ms. Stone says.

Usually, leaf galls occur around bud breaks or as new leaves begin to unfold. Twig and stem galls are solid and woody.

Insecticides won't prevent them because the larvae are protected in the gall's armor. Sprinkling carbaryl on a tree infected with leaf galls when the buds are just opening in the spring could slow the growths. But this can be a tough task. The easiest way to get rid of galls is to prune them out of the plant.

Scientists say plants form them to help them fight off bacteria, fungi, mites, mistletoe, and other pests.

Ms. Stone says once you notice galls, it's too late to treat them. "To control them over the winter, rake the infected leaves and destroy them," she says.

Some of the more aggressive growths like crown gall and peach leaf curl can affect orchard trees. Crown gall is found at the base of fruit trees and peach leaf curl causes the leaves to become deformed.

Every plant forms a different gall shape. Mistletoe can leave its mark on a tree long after it is gone. Galls caused by mistletoe may be several feet in diameter. Cone-bearing trees may have mistletoe battle scars that look like witches' brooms near the tops of trees.

Keep your junipers away from apple trees. Some galls, called "cedar apples," are caused by rust fungus and decorate many junipers. These reddish balls hold spores that can infect nearby apples, crab apples, and apple trees.

Have more gall questions? Call the Lucas County Extension hotline - 419-578-6783 - from 10 a.m. to 1 p.m. Mondays, Wednesdays, and Fridays.



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