From: AgAnswers
An Ohio State Extention and Purdue Extension partnership

A new soybean plant variety hitting the market that shows genetic resistance to all known races of soybean cyst nematode may change the way soybean growers manage the pest.

However, the product shouldn't be considered a cure-all. Traditional management practices are still important, stresses an Ohio State University plant pathologist.

CystX, a patented technology owned by Purdue Research Foundation, offers broad-based resistance to soybean cyst nematode in that it prevents the pest from reproducing on the plant's roots. OSU plant pathologist Mac Riedel said the technology is a good way of controlling soybean cyst nematode populations but other management practices, such as soil sampling and crop rotation, should not be forgotten.

"With such a product on the market, it will be very easy for growers to continuously plant the resistant variety year after year after year. It's just a natural tendency," Riedel said. "But, like with other varieties, eventually females will be selected that will be able to reproduce on this line and we will be back to where we started."

Hence, the importance of crop rotation, Riedel said. "It's so easy to control this pest," he said. "All you have to do is rotate your crops."

Soybean cyst nematodes (SCN) feed on the roots of young plants, which prevents roots from taking up vital nutrients. The result is a drop in yields and economic losses. The best management tool to control SCN populations is to sample fields with a history of problems and rotate resistant varieties based on relative egg counts.

Yield loss threshold of SCN begins at 200 eggs per cup of soil. At 2,000 eggs per cup of soil, most susceptible soybean varieties suffer significant economic losses. At 5,000 eggs per cup of soil, growers should avoid growing soybean varieties altogether, even resistant varieties.

Riedel said that growers should keep this in mind even when planting a resistant variety like CystX or a resistant soybean variety with similar Hartwig-type resistance. One reason is based on Ohio State research that has shown a persistent weed called purple deadnettle to be a host for soybean cyst nematode.