Released May 29, 2008
MANHATTAN, Kan. - Many of nature´s tiny flies, mites and non-stinging wasps love oak- furnished nurseries. They represent hundreds of insect species, all of which lay eggs on oak trees.
"Tree owners get concerned every spring, seeing the effects of this abundance," said Ward Upham, Master Gardener program coordinator for Kansas State University Research and Extension.
Owners´ worry is that the insects also inject the host tree with a growth-regulating chemical. The oak itself reacts, and the result on the tree is an abnormal growth - a gall - for every insect offspring.
"Depending on the oak variety and its location, galls can show up on a tree´s leaves, twigs, stems, buds, flowers or bark. Occasionally, they´re on acorns and roots," Upham said. "We´re just lucky that most gall-maker insects don´t cause significant tree damage."
Galls can cause enough leaf deformity, however, to make a tree unsightly, the horticulturist added. Severe twig-gall infestations can cause twig dieback. But, even that rarely leads to tree death.
"I´ve seen twigs that looked like a solid mass of galls, yet still leafed out in spring," he said.
Galls can be round, lumpy, dish-shaped, spiny, flattened, elongated or star-shaped. Although many are in the BB to gumdrop range, their size can range from a fraction of an inch to several inches.
Each gall-maker species produces its own particular shape, size and color of gall. In turn, each gall serves as a hatchling´s cover and sole food source until the larva pupates into an adult, Upham said.
"If the timing for all this seems a bit vague, the reason is the amount we still don´t know about gall makers," he said. "In North America alone, we´ve documented more than 700 species of gall wasp."
In fact, their protected young and life cycle variations make controlling gall-makers impossible.
"You can prune off stem and twig galls, if that seems practical and necessary," Upham said. "Otherwise, your best course is to try to ignore the problem or perhaps trim to improve tree appearance."
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http://www.oznet.ksu.edu/news/
Contact: Mary Lou Peter-Blecha, (785) 532-1164, mlpeter@ksu.edu
