A report published in Weed Technology indicates that it will be necessary to broaden the scope of weed management systems for glyphosate-resistant (GR) crops. Glyphosate is the main component of many weed control products used in GR cropping systems.

The study, “U.S. Grower Views on Problematic Weeds and Changes in Weed Pressure in Glyphosate-Resistant Corn, Cotton, and Soybean Cropping Systems” (Vol. 23(1):162-166), is important because it shows that effective crop management depends on continual analysis of weed management systems and on adapting these systems as weeds evolve and become resistant to herbicides, especially glyphosate.

Growers of GR corn, GR cotton, and GR soybeans from six U.S. states were asked to describe their perceptions of problem weeds, weed pressure, and tillage. The results will help researchers develop weed management systems that may include glyphosate but that also utilize other herbicides and management techniques such as tillage and more diverse crop rotations.

Weed pressure was considered moderate or light by most GR crop growers. The weeds reported as being the most problematic due to their tolerance or resistance to glyphosate were ragweed, johnsongrass, velvetleaf, morningglory, sicklepod, pigweed, and water hemp. Thus, weed shifts will occur as these weeds continue their crop invasion and as other weeds evolve and become resistant. With regard to tilling, the researchers found that growers tended to underestimate the advantages of tillage on weed pressure.

Although some growers of solely GR crops reported no major weed problems, there were more growers using a GR crops/non-GR crop rotation who reported no major weed problems. This advantage will likely prompt more growers to switch to rotational methods of weed management.

As weeds become resistant to management techniques, there will be a need to ensure the sustainability of crop management systems by broadening their scope and ensuring that they include crop rotation, tillage, and herbicides other than glyphosate.