The use of residual herbicides in Roundup Ready cropping systems improves control of tough weeds such as lambsquarters, pigweed and wild buckwheat, and it reduces the potential for development of weed resistance, according to Monsanto, the manufacturer of Roundup.

These are two clear findings from an extensive, decade-long weed-resistance study conducted at multiple irrigated and non-irrigated sites across four states: Nebraska, Colorado, Kansas and Wyoming. The research encompassed a continual rotation of Roundup Ready crop technologies in corn, soybeans, sugarbeets and spring wheat.

The purpose of the study was to create an environment of continuous Roundup Ready crops to determine if, when and how weed resistance to glyphosate might develop over time. After 9 years of use of full rates of Roundup, there was a shift in weed population to common lambsquarters.

However, where a residual herbicide was used at planting in conjunction with Roundup herbicides applied over the top in Roundup Ready Corn, lambsquarters was again controlled, according to Robert Wilson, a weed scientist at the University of Nebraska and an academic principle in the study.

Wilson notes that pre-emergence residual herbicides are economical and adds, “Once the farmer has to contend with a weed shift to hard-to-control weeds, he gets a good return on his herbicide investment when residual herbicides are used.”

Roundup Ready wheat is not commercially available.