Soybean sudden death syndrome (SDS) had a good year in 1998.
This more-or-less silent killer sneaks up on growers, attacking the best beans at a time when everything seems to be going great.
Since first identified about 10 years ago in west-central Indiana, SDS can now be found from Ohio to Missouri, Iowa and Wisconsin, and farther south in Arkansas and Kentucky.
It's caused by fusarium solani, a common soil-borne fungus. And, says Walker Kirby, a University of Illinois extension plant pathologist, it's often found in conjunction with soybean cyst nematodes (SCN).
But you don't have to have SCN to have SDS, says Mike Stumpf, who farms near Columbia, IL, with his brother Ron.
The Stumpfs say SDS seems to show up more in beans that have been planted early in cool, wet soils. And, to their dismay, it hit their Roundup Ready beans harder than others this year and last.
"One early planted bottom field of Roundup Ready beans was a disaster," Mike reports.
He isn't suggesting that growers not plant Roundup Ready soybeans, though. The same variety planted about 2 1/2 weeks later on similar soil turned in one of his top yields this year.
"I like the Roundup Ready technology," he says. "But until we have a better idea of how to manage SDS, I'm going to be a lot more careful how I use it."
X.B. Yang, an Iowa State University extension plant pathologist, has been monitoring the movement of SDS into Iowa.
"In 1994, we verified it in only four counties in the state. By '98, it had shown up in 31 counties in southeastern and central Iowa," he says.
Like the Stumpf brothers, Yang and Kirby say there's evidence to suggest it's being reported more often in Roundup Ready soybeans. But, like the Stumpfs, they draw a line at recommending against planting those varieties.
Monsanto made the Roundup Ready technology available to seed companies by providing seed of a variety into which the gene had been incorporated. Yang says the original glyphosate-resistant variety may have been highly susceptible to SDS.
Kirby cites other possible reasons growers are seeing more SDS in Roundup Ready beans. One is that farmers look at those beans more often, since they pay more for the seed and are a little uneasy about spraying a crop with Roundup.
The prevalence of Roundup Ready beans may be another factor, says Kirby. They were planted on at least half the soybean acres in some areas this year.
"I have seen no proof of any genetic linkage between the Roundup Ready gene and SDS," says John Rupe, a University of Arkansas plant pathologist.
Adds Dennis Byron, Pioneer's director of soybean research: "We can't confirm any differences in disease resistance between Roundup Ready and non-Roundup Ready soybeans.
"We do know that the donor variety Monsanto distributed was highly susceptible to SDS," says Byron. "But the Roundup Ready varieties we're selling are many generations removed from that variety. We feel there has been enough crossing away from the original donor variety that its susceptibility should no longer be relevant."
He does, however, urge growers to check disease-resistance ratings before buying seed and to avoid planting varieties with low SDS resistance on fields where the disease has been identified.
"In many cases last year, Roundup Ready was the first criterion growers wanted when they went looking for soybeans. It's a good technology, but growers need to check for other important traits as well, including standability and resistance to all diseases that might be a problem in their areas."