More Soybean Rust Found in Iowa Fields

The aggressive soybean disease, new to Iowa, was identified in two more counties in the state last week.

Published on: Oct 17, 2007

Soybean rust is an aggressive fungal disease that's new to the Upper Midwest, and last week it was found in two more counties in Iowa. USDA officials and Iowa State University crop disease specialists made the announcement on October 10. The first confirmed case of soybean rust ever in Iowa was found in a field in Dallas County in central Iowa in September.

"The disease was found in Polk County in central Iowa on October 10 and in Fremont County in the southwest corner of Iowa also on October 10," says Darren Mueller, an Iowa State University Extension plant disease specialist. "It has shown up too late in the season this year to hurt yields. And the spores won't survive the winter cold."

This yield robbing disease is a problem in Brazil where soybean growers have to spray fungicides to control it. The disease spores are blown into Iowa from the southern United States, where soybean rust was first discovered in 2004. It is believed to have been blown into the U.S. at that time by hurricanes.

Finding rust in Iowa isn't a big surprise

Soybeans in Iowa are already mature and being harvested. Thus, the fungus won't cause damage this year in Iowa and the Midwest, even though it is expected to continue to spread north as the year progresses.

"We were not surprised that rust was confirmed in two more fields in Iowa last week - in Polk County and in Fremont County," says Palle Pedersen, ISU Extension soybean agronomist. "That follows the confirmation of the rust infection that was found on soybean leaves in Dallas County on September 25."

Polk County is adjacent to Dallas County in central Iowa. Does that mean this area was favorable for rust a few months ago? "The bottom line is that the conditions we had in late August and in September, with heavier-than-normal rainfall, most of the state was experiencing conducive conditions," says Pedersen. "The past few years we've been looking for the disease and we've been able to find it late in the season this year."

Prepared for, but not worried about rust

Since the disease first came into the southern edge of the U.S. several years ago, people have been wondering if the spores would blow north into Iowa. It was as close to a non-story as could be. It just didn't show up in Iowa. Everyone seemed to be talking about the possibility of rust invading the Midwest and everyone was preparing for the disease to eventually get to northern states like Iowa. Farmers and crop specialists were prepared but not worried.

Is Pedersen still of that mindset? "Yes I am," he says. "I really think the way the system is set up now, with the sentinel plots and all the information we have gathered and given to farmers the past few years, we are prepared for this. Farmers should pay attention to this disease but not be worried about it. I think we have done all that we can to prepare for rust. We can identify it. It came into the U.S. so late in the growing season this year that there is nothing anyone should really worry about."

Pedersen adds, "I think we are ready for 2008 as well, to go out and scout fields and do the best job of watching for rust and controlling it. You need to identify it as early as possible in the growing season. We may need to spray fungicides to control and we want to make sure farmers don't lose any significant amount of yield to this disease - if it does show up earlier in the growing season."

Is fear of rust causing farmers to spray?

6+Has fear of rust attacking soybean yields in Iowa and the Upper Midwest driven more farmers to spray foliar fungicide on soybeans? Or was the trend already there for Iowa farmers to explore and try the use of fungicides on their farms.

"No doubt, after rust was first confirmed on soybeans along the southern edge of the United States in 2004, more farmers even as far north as in Iowa, went out and looked at the impact of fungicides in soybeans," says Pedersen. "We have done a tremendous amount of research throughout Iowa on the use of foliar-applied fungicides to soybeans. So have our neighboring states. In general, we get very little infestation of foliar diseases in soybeans this far north."

The economics of using foliar fungicide is so variable in northern states like Iowa, and when you do get a positive yield response it's usually not enough to cover the cost of the spray and the application, he says. "I still think that's the way it is going to be," says Pedersen. "These fungicides have been developed and been on the market since the mid-1990s. If there really was a consistently profitable yield response from using foliar fungicides on soybeans, we would have been recommending farmers spray their beans a long time ago."

Doesn't think rust will be a big problem

"We will continue to do research and we will continue to do everything we can to help farmers boost soybean yields," he adds. "But right now I don't think it will pay for farmers to use a foliar fungicide in Iowa. In 2007, we had the wettest August on record. The rust disease this year showed up in late September and early October when most of the bean crop has already been harvested. The timing of that infestation this year was great news for all of us."

The Iowa Soybean Association's On-Farm Network has worked with farmers trying the use of foliar fungicides on soybeans in their fields. They are trying to determine if application of foliar fungicide sprays is cost-effective. Of course $9 per bushel soybeans is more cost-effective than $5 soybeans.

The discovery of rust has caused farmers to become aware that there is a threat to their soybeans. Farmers have traditionally focused on managing their corn crop more so than their soybeans. Now, people are paying attention to their soybeans more, says Pedersen, and they seem to be challenged to see if they can raise their yields on soybeans. Perhaps the increased overall management of soybeans is what we are seeing rather than the addition of one input, such as a fungicide application.

Most producers have always said they are corn farmers first and soybeans are a second crop. But when you get into a year like 2007, you can lock in $8.50 beans for next year, for a little bit of a premium on some "put" options. Based on where the markets are currently, you may see corn acreage snap back probably quite dramatically in the United States. And you will see farmers spend more on products to try to increase their soybean yield.

When you see Kip Cullers, the new world soybean growing champion from Missouri, set a record that went from 139 bushels of beans per acre last year to 154 this year, that indicates you may be able to increase your bean yields from 50 to 60 bushels per acre over a time period if you carried out the right kind of management practices.

If you want to truly manage your soybeans, you have a lot more tools today than you've ever had, notes Pedersen.