Cleansing Technique May Benefit Potato Crops
By Jan Suszkiw
March 7, 2002
Rotating potatoes with alfalfa or
spearmint may offer farmers a sustainable way to reclaim crop soils
contaminated with corky ringspot disease, Agricultural Research Service studies
Corky ringspot--a brown, bulls-eye blemish on tubers--is caused by the
tobacco rattle virus, which is passed into potato plants by wormlike soil
organisms called stubby root nematodes. In affected areas such as
Washingtons Columbia Basin, where 5,000 acres are contaminated, potato
farmers have either stopped growing the crop altogether or resorted to
fumigating soil to kill nematodes that spread the virus.
At $250 per acre, however, fumigation is expensive. Plus, it kills soil
organisms other than nematodes. A more sustainable, pest-specific approach
could come from rotating potatoes with alfalfa or spearmint to rid the
nematodes of their viral payload, according to scientists Rick Boydston, Pete
Thomas and Hassan Mojtahedi. Boydston and Thomas are at ARS
Vegetable and Forage Crop Production
Research Unit in Prosser, Wash. Mojtahedi works for
Washington State University.
Their strategy is based on two observations: First, the virus cant
survive in alfalfa or spearmint, so the nematodes cant acquire it while
feeding on the plants roots. Second, the nematodes naturally shed the
virus from their bodies by molting. Given enough time, the scientists reasoned,
nematodes that fed only on these plants eventually would rid themselves of the
virus, and thus pose little or no danger of infecting a subsequent potato crop.
Indeed, in greenhouse trials, virus-bearing nematodes that fed on potted
alfalfa or spearmint plants for three months lost their ability to infect
disease-free potato plants. Conversely, nematodes that fed on tobacco, a
natural host of the virus, retained their ability to infect disease-free potato
Some farmers already practice this rotation but still fumigate fields with a
previous history of corky ringspot. The key, scientists emphasize, is to
eliminate weeds in alfalfa or spearmint crops where nematodes can acquire the
virus. These include hairy and black nightshade, downy brome, common chickweed
and prickly lettuce. They are among 38 weed species the scientists have tested.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.