Barry Fugatt: Gall-wasps to blame for strange growths on trees
BY BARRY FUGATT Garden World
Saturday, August 25, 2012
8/25/12 at 4:00 AM
I enjoy a good mystery. And a dandy one is being played out in local gardens. It involves the mysterious relationships between tiny gall-wasps and plants.
It's no mystery that gall-wasps exist. Fossil records indicate that they have been flittering around the natural landscape for more than 300 million years. North America alone is home to more than 500 species. The challenge is to understand the complex relationship between gall-wasps and their plant host.
Gall-wasps are minute, not much bigger than fruit gnats, and dart about over a bowl of decaying grapes or bananas. Although tiny, gall-wasps pack a potent punch. They cause some plants to form an assortment of tumor-like growths on stems and leaves.
Locally, several gall-wasp species attack oaks. It's as if a tiny gnat-size insect says to an oak: "I'm going to prick you on a leaf or stem and lay a few eggs in the wound. I expect you to respond by building me a house, and not just any house. I want the house to be a specific size, shape and color. And while you're at it, stock my new house with high-protein provisions for my developing young."
Incredibly, the mighty oak obeys and produces the colorful, ornate galls (insect homes) we commonly see attached to oak leaves and twigs in late summer.
Frankly, I find this insect/plant relationship to be utterly amazing. Heck, I could rarely get my kids to clean their rooms, much less build me a house.
Although short on specifics, entomologists suspect that during the initial egg-laying process (pricking of a leaf or stem) gall-wasps pass along a powerful, microscopic speck of growth regulator that somehow overrides the host plant's own genetics in the affected area, causing the plant to produce a specific tumor-like growth that houses the eggs.
Leaf galls come in many shapes and sizes. Some resemble miniature stars, sea urchins, cones, cups, balls or saucers. "Oak Apples," green golf-ball size growths, are common on Tulsa-area oaks. When the spongy gall is cut open, a tiny larva can be found developing in a separate, hardened chamber in the center of the growth.
Don't panic when you see leaf galls. They are generally harmless to plants.
Other galls, such as the Horned Oak Gall - which forms hard, woody growths on oak limbs - can be injurious. Such growths may impede the normal flow of water and nutrients through a branch. Pruning infected branches may be helpful. Pesticides are rarely effective, however.
Plant galls have played interesting roles in history. Leonardo da Vinci, Rembrandt and Vincent van Gogh all prized ink made from crushed oak galls. Tannic acids in the galls made the ink nearly impossible to erase.
Other galls have been used for cosmetics, food and jewelry through the ages.
Original Print Headline: Gall-wasps sublease area plants and trees
Barry Fugatt is director of horticulture at the Tulsa Garden Center/Linnaeus Teaching Garden. He can be reached at 918-746-5125 or at bfugatt@tulsagardencenter.com.
Associated Images:
Leaf galls, tumor-like growths on trees, come in many shapes and sizes. Some resemble sea urchins, balls or saucers. They are generally harmless to plants, though some may impede the normal flow of water and nutrients through a branch. These oak apple galls are typical in Tulsa. Courtesy
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