Asian soybean rust confirmed in central Iowa
Tests confirm a small find of Asian soybean rust (ASR) in a soybean field in Dallas County, in central Iowa, officials say. This is the northernmost rust find in the U.S. to date.
The discovery of a soybean leaf with approximately nine rust pustules on it was made by an agronomist in a commercial soybean field this week, and further testing at Iowa State University (ISU) confirmed the disease, according to Iowa Soybean Association director of contract research David Wright.
"It was a very small area that was showing pustulating lesions. It was a very lucky find," Wright says. "Further observation of the fields didn't find any other leaves with pustules, but after several leaves were taken back to the lab and incubated, they developed pustules."
The process of confirmation, from when the sample was first taken to when officials found the sample to be ASR-positive, took about a day and a half, Wright adds. This is officially the second rust case confirmed in the state of Iowa after soybean residue found in a grain bin last year tested positive for the disease.
"The one last year was officially Asian soybean rust. We just could not confirm it came from the field it was reported to have come from," Wright says. The sample was confirmed ASR-positive in March.
The rust discovery will likely have a minimal effect on Iowa's soybean crop, a "fortunate" thing for the state's soybean farmers, according to Curt Sindergard, Iowa Soybean Association president and a soybean grower from Rolfe
"This is an important find for Iowa soybean growers," Sindergard says. "It confirms that soybean rust can develop in Iowa. We are fortunate that this disease was found at a time when it will have little economic impact for soybean producers."
At this point, Wright says the lion's share of the state's crop is in the R6 or R7 development stage. But, because of heavy rains around planting time in some parts of the state, some beans were late getting into the ground. It's with these later-planted fields where growers are encouraged to remain watchful and be ready to treat, if the need arises.
"There is nothing to worry about for the majority of Iowa's soybean acres. Most are at R6, ready to be harvested. There are few acres in Iowa there were planted late that are at the R4 stage, and those might be susceptible," Wright says. "If late-planted soybeans are infected, growers may want to spray those. but, for the most part, it really is a non-issue because it is really too late in the season to do anything."
Friday's rust announcement is no surprise to Wright, he says, especially considering growing conditions in the southeastern U.S. this year. The Iowa rust find is well in line with prediction models developed by ISU plant pathologist X. B. Yang.
"X. B.'s prediction models have been 100% accurate since 2004. The drought in the southeast really played a huge role in slowing down the progress of Asian soybean rust moving north. But once it started, it was found in Louisiana, then moved into Texas," Wright says. "So, it was just a matter of time before it was found in central Iowa and points further north."