URBANDALE, Iowa - The Iowa Soybean Association (ISA) cautions Iowa soybean producers to be vigilant in the next few weeks as late-planted soybeans reach maturity. Asian rust was found in a soybean field in Dallas County on Tuesday, September 25. The disease was confirmed using molecular techniques conducted by a reputable company. The presence of soybean rust was also confirmed by Dr. X. B. Yang, plant pathologist, Iowa State University, one of the world’s experts on Asian soybean rust.

“This is an important find for Iowa soybean growers,” says Curt Sindergard, Iowa Soybean Association president and a soybean grower from Rolfe. “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.”

Soybean rust could cause damage to Iowa’s late-planted soybeans. Early planted soybeans may be less at risk if they are at the R6 growth stage or later. After R6, there appears to be no economic advantage to treating fields with fungicides according to Dr. David Wright, ISA director of contract research. R6 is defined as: full seed – pods contain green seed that fills the pod capacity at one of the four uppermost nodes on the main stem.

“We recommend that soybean growers scout fields with soybeans at the R4 to R6 growth stages to determine their overall risk,” says Wright. “Most Iowa soybean fields are likely mature enough that producers need not spray this season.”

Wright also says soybean producers should be acutely aware that fungicides have a pre-harvest interval during which growers should not harvest fields. Be sure to consult your crop advisor before applying fungicides.

“Scout late-planted fields first, particularly those that retain moisture from morning dew,” says Wright. “First, determine soybean growth stage. Then look for infected leaves in the lower canopy. Look at the underside of lower leaves for small volcano-like structures. The opening of these structures will be round, not linear. A 20-30X hand lens is recommended.”

The ISA and Iowa State University have partnered to train more than 650 agricultural professionals to serve as First Detectors. These people have been trained to identify soybean rust and are part of a nationwide effort to minimize the impact of rust. You can find your local First Detector by logging on to www.soybeanrust.info and entering your ZIP code. Or check with your local certified crop advisor to determine if they’ve been trained by Iowa State University as a First Detector for soybean rust.

If you suspect you have found rust in your soybean fields, call your local First Detector or send a plant sample to the Crop and Diagnostic Clinic, 351 Bessey Hall, Iowa State University, Ames, IA 50011.