Weeds

More than 55 weed species, including 10 confirmed herbicide-resistant species, threaten soybean yields each year in fields across the state. As farmers shift to more no-till soybean production, weed specialists are seeing a rise in perennial weed species. Illinois farmers have identified waterhemp as one of the most problematic weeds.

Such findings are just a slice of the work being coordinated through the Checkoff's managed weed research program. Weed scientists from the University of Illinois Urbana-Champaign, Southern Illinois University Carbondale (SIU), and Western Illinois University are studying weed challenges and looking at the effects of herbicide application and management practices on weed control in Illinois soybean fields.

  • The University of Illinois Weed Science site contains additional information about soybean Checkoff-funded research. You will also find links to Extension, faculty, weed references, and weed identification. Another valuable resource located here is A Pocket Identification Guide of Early-Season Weed Species, initially developed with funding from the soybean Checkoff. The guide includes color photographs and descriptions of 19 weed species.
  • Checkoff-funded research in Illinois finds that soybean growers utilizing continuous no-till systems will have significantly greater populations of winter and summer annual weeds. Winter annuals may be more of a problem under high-fertility levels. Summer annual weeds may be more prolific under low fertility, possibly due to less vigorous crop growth. On a similar note, research related to black nightshade acting like a perennial weed, most commonly in no-till, is available at the SIU Weed Science site.
  • Winter annual weeds have become a management problem for many growers in Illinois. Field identification of winter annual grasses is often difficult because several species are similar in appearance. Researchers have developed a winter annual grass identification guide. To obtain a copy of the guide, go to the publications section of the SIU Weed Science site.
  • SIU's 2005 Weed Research Annual Report is now available online. The report contains the downstate field report results of a variety of weed studies in soybeans, including studies involving adjuvants, fall-applied herbicides, and weed control in no-till and conventional tillage settings. Weed control information for other crops is also available at the site.
  • Obtain the latest information on herbicide adjuvants from the Compendium of Herbicide Adjuvants, prepared by Bryan Young, SIU weed specialist. The eighth edition contains 523 entries from 39 companies. The guide contains principal functioning agents, use range, and comments for each product. Visit www.herbicide-adjuvants.com to review details.
  • Over the past two years, Checkoff-funded research has allowed university scientists to evaluate the emergence, competitive influence, and possible control for hophornbeam copperleaf—an annual weed species that does not begin to emerge until the first week of June and continues to emerge as long as soil moisture is adequate and soybean canopy development is not complete. So far, studies have found that hophornbeam copperleaf is not as competitive as other broadleaf weeds such as waterhemp. Soil-applied and postemergence herbicide options can provide a high level of control, especially when post herbicides are applied to plants less than 6 inches in height.
  • Researchers at SIU are exploring the interaction of winter annual weeds and soybean cyst nematode (SCN). Henbit and purple deadnettle—both winter annuals—can host SCN during the fall, winter, and spring. Researchers want to determine the effect these weeds have on SCN populations and whether henbit and purple deadnettle should be considered in an integrated approach to managing SCN.
  • As soybean varieties, weed species, and production practices change over time, SIU researchers are interested in determining whether the recommendations for preventing weed competition should also change. Current studies are investigating various scenarios to ensure appropriate recommendations are developed for conditions present in most soybean fields. For example, while weed control at the end of season is believed to result in the greatest soybean yields, researchers are learning this may only be true when weeds are managed starting with soybean planting. If any early season competition from tall weeds occurs—even with the same level of late-season weed control—one study reveals that soybean yields can be cut by 11 bushels per acre from early-season competition.