Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
8/4/00
Contacts:
Greg Tylka, Extension Plant Pathology, (515) 294-3021,
gltylka@iastate.edu
Micheal Owen, Extension Agronomy, (515) 294-1923, mdowen@iastate.edu
Julie Todd, Extension Communication Systems, (515) 294-2405,
jtodd@iastate.edu
Clean Fields but Low Yields?
AMES, Iowa -- Research conducted by a multidisciplinary team of Iowa State University scientists from 1996 through 1999 revealed that using herbicide-resistant soybean varieties without considering control of other pests could have serious economic consequences.
The research, funded by Iowa soybean checkoff dollars, was conducted in fields infested with the soybean cyst nematode (SCN). "As much as 75 percent of Iowa fields are infested with this serious economic pest," said Greg Tylka, ISU Extension plant pathologist.
Several herbicide-resistant and traditional soybean varieties were grown in each field experiment. Weeds were managed by a conventional herbicide program, a targeted weed management program using the herbicide for which the soybean cultivars were resistant, or a mechanical weed management program that kept the plots weed free. The average dollar return per acre was calculated for each treatment.
The two varieties in the experiments that were resistant to SCN, a Roundup Ready/SCN-resistant variety and a conventional, public variety named Jack, consistently produced the greatest yields. Jack with conventional herbicide weed management had the greatest economic return on yield at several soybean-selling prices. Also, there were lower end-of-season SCN population densities where Jack and the Roundup Ready/SCN-resistant variety were grown compared with plots planted with the SCN-susceptible varieties.
"Such a reduction in SCN numbers will improve the profitability of future soybean crops grown in these fields," said Tylka. "Our results illustrate that growers must consider all pests that might affect yields when making management decisions concerning soybean production."
Micheal Owen, ISU Extension weed scientist, concurred and stated, "The manner of controlling weeds is not important but controlling weeds without considering other pathogens and insects is wasted effort."
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