Whatever happened to soybean rust?
The scare over soybean rust last decade could have jokingly been referred to as the “Agricultural Media, Chemical Company, and Plant Pathologist Full Employment Act of 2005”.
That year, farm magazine articles detailed how this disease could shred soybeans. Chemical companies geared up its fungicide arsenal to deal with any outbreaks. Farmers anxiously awaited updates from industry and university plant pathologists regarding disease movement.
There was good reason. Soybean rust had devastated Brazilian soybean production for several years prior to its United States arrival in late 2004. Many feared a repeat in the United States.
Fortunately, the dire rust predictions of that day never materialized.
“We haven’t seen it come up to the U.S. in a big way since then, but it has come into southern states,” says Paul Stephens, Pioneer senior research director for soybean product development. “What we found out is ultraviolet light reduces the survival of the rust spores.”
The Brazilian province of Mato Grosso, where much of that nation’s soybean production occurs, has many cloudy days. With less ultraviolet light via sunshine compared to the Midwest, the disease thrived.
Fortunately, the numerous sunny days in the U.S. put the kibosh on the disease, particularly in the Midwest. Rust must also have a living host to survive. Each year, the freeze line drives the rust pathogens back to the South. For rust to gain a foothold, spores must blow in from the South the next year.
Yield loss has occurred in unsprayed fields in the South.
The threat hasn’t completely vanished in the Midwest, either.
“We can have some exposure, perhaps a one in a one-in-thirty year event, but we can never be sure,” says Stephens.
That’s why Pioneer is developing native and transgenic traits that resist soybean rust. “Asian rust is a dynamic pest, one that can quickly overcome native genes,” says Stephens. “It has done this in South America, so we have a transgenic project in place to give us a more durable level of disease resistance.”