Cornell Researchers Combat The Onion Bulb Mite

February 12, 1997

LIVERPOOL, N.Y. -- Once just an unnoticed arthropod minding its own eight-legged business, the onion bulb mite -- Rhizoglyphus robini -- is rearing the ugly side of its docile personality. Barely visible to the naked eye, the mite has begun to attack some of New York's prized onion fields, and Cornell University scientists want to stop it. "For a number of years now, it has caused economic losses," said Charles J. Eckenrode, Cornell professor of entomology and researcher at Cornell's Agricultural Experiment Station in Geneva, N.Y. "We don't have a lot of answers right now, because so little is understood about this problem. However we believe that careful research will come up with the necessary answers."

Eckenrode will discuss the mite and other onion pests in "Onion Arthropod Management" at the New York State Vegetable Conference on Thursday, Feb. 13, at 9:10 a.m. in the Cotillion Room at the Four Points Hotel in Liverpool.

"Why is it suddenly a problem? I don't know, but we will be looking at conditions in the field that may have caused the mite outbreaks," Eckenrode said. The mite attacks the onion seed before it becomes a seedling or as a very young seedling. Growers can recognize the problem by the reduced stands or the wilted seedlings. One theory that Eckenrode's group is investigating is the use of grasses as windbreaks, which keep valuable soil from becoming dust in the wind. These grasses may be harboring the mite until it moves to the onions.

However, windbreaks are very important in onion production. Traditionally, New York's famous cooking onions are grown in muck -- a highly organic, peat-type soil rich in nutrients -- and once the muck is gone with the wind, it is lost forever. With an annual crop value of between $50 million and $75 million, onions are one of New York's most valuable crops, and growers don't want to be out of muck.

Onion growers are painfully aware that it does not take much to ruin a valuable acre of onions. Orange County, N.Y., onion growers have noticed R. robini is becoming more of a pest each year. Combined, there are about 12,000 acres of onions being grown in New York. The average grower invests $2,500 to $3,000 into each acre, before any crop is harvested. Cornell Cooperative Extension estimates that perhaps as many as 1,500 acres in Orange County have been affected by the mite -- 25 percent of all the onion acreage in that county and 12.5 percent of the onion acreage statewide.

Wind barriers, such as snow fences, or planting basket willows or growing shaded plants, or even growing other crops such as barley or oats, serve to keep the soil in its place. But, Eckenrode said that no matter what a grower does -- even installing a windbreak -- may provide some kind of niche for harboring pests. So it is the researcher's job to understand what sort of niche a new pest is occupying and how this pest is affecting the crop.

"Farmers always go through change. As soon as you change something, a living system will take advantage of that change. That may be what's happening with the bulb mite, but we won't know until we study it," Eckenrode said.

Other Cornell scientists are joining in the research. Richard W. Straub, Cornell professor of entomology and located at the Hudson Valley Lab, performs mite research in nearby Orange County. Michael G. Villani, Cornell associate professor of entomology at Geneva, also is studying the mite at the experiment station.

Ariel Diaz, Cornell graduate student in entomology from Ponce, Puerto Rico, has initiated a research program dealing with the behavior of the mite. So far, his worldwide literature search has found little on this pesky arthropod as it relates to onions. That's why Eckenrode thinks that he might have to literally start from scratch on this research.

While mite damage in Orange County onion fields increases, the researchers have yet to find proven management techniques. If the windbreaks prove to be an important link, then manipulating how they are planted may become necessary. The entomologists have tested chemicals for control using mite colonies in the laboratory, with only limited success.

In a survey of four infested onion fields last year to determine seasonal patterns and abundance of the bulb mite, mite presence was detected, but the numbers counted did not correlate with the economic damage.

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