7/26/01

Contacts:
Greg Tylka, Plant Pathology, (515) 294-3021
Brian Meyer, Agriculture Communications, (515) 294-0706

AFTER ALL THESE YEARS, SOYBEAN PEST'S DAMAGE STILL DRAMATIC

AMES, Iowa -- Few things surprise Greg Tylka about a soybean pest he's studied for almost 12 years. Still, there are times in the nematologist's work when the seriousness of the problem is dramatically reinforced.

Tylka, an Iowa State University plant pathology professor, has been conducting experiments examining yield of soybean varieties that are either resistant or susceptible to soybean cyst nematode (SCN). Last year, the varieties were grown on two farms, one known to be infested and the other SCN-free.

The yield difference was dramatic. Average yield on the SCN-free farm was nearly 40 percent greater -- 52 bushels per acre versus 38 bushels -- than yield from plots on the infested farm.

Tylka believes low yields at the SCN-infested farm potentially were due to the interaction between SCN and herbicide injury. In the experiments, he examined how plants recover from injury that occurs after herbicides are applied. On both farms, the herbicide treatments stymied plant growth for awhile, but yield was significantly reduced only on the SCN-infested farm.

"That was the most significant interaction we noticed," said Tylka, who also examined how SCN interacted with tillage and weed management.

On both farms, few differences were noted between the growth of SCN-resistant and SCN-susceptible soybean varieties. But in all cases, the resistant varieties yielded better.

For soybean growers, the findings should emphasize the importance of managing stresses in fields that have SCN, Tylka said. "If you have SCN, you need as healthy a crop as possible to mitigate damage. Other stresses can aggravate SCN damage."

Tylka estimated that three out of four Midwestern soybean fields are likely to have SCN infestations. In Iowa, economic losses due to the pest are estimated in the tens of millions of dollars each year.

A dramatic sidebar of Tylka's recent experiments was the potential explosiveness of SCN populations. No nematode eggs were detected in early spring soil samples taken from one field chosen for the experiment. After 64 experimental plots were established in the SCN-free field, soil samples were collected from each plot and tested for SCN. SCN was found in very low numbers in only six plots. But after the crop was harvested, Tylka re-tested plots on the SCN-free farm for the presence of the pest and found some with tens of thousands of SCN eggs.

"It proves that not finding SCN in a soil sample doesn't mean it's not present," said Tylka. "You can have infestations that blow up in a year's time. There's no such thing as having a little SCN. As soon as it's detected, you should begin managing it."

Tylka advises scouting for SCN six weeks after planting through late August. "Now is a perfect time to be out there digging soybean roots and looking for the little white SCN females," he said. More information on scouting can be found by clicking on "Extension" on Tylka's website, www.exnet.iastate.edu/Pages/plantpath/tylka/Frames.html.

This year Tylka is repeating his experiments. He and colleagues also will focus on any interactions between SCN and brown stem rot.

Tylka's work is part of the Yields Project, a multistate research program funded by Iowa and Illinois checkoff dollars through the Soybean Research and Development Council (SRDC). The Yields Project is one of the largest soybean research projects ever undertaken to understand factors that limit soybean yields. The project involves scientists at Iowa State, the University of Illinois, the University of Wisconsin and Southern Illinois University.

News Releases Agriculture in Action Ag Online Communications Skills Home