Roundup. Glyphosate. We can’t seem to live without the chemistry, but we may soon find that although it has changed our approach to weed control, we may have to find a new approach. While some weed species and some scattered weed patches have become immune to the toxicity of glyphosate, weed specialists in a half dozen states coordinated their efforts in a Benchmark Study on Glyphosate Resistance Management. Here’s what they found….

Twelve hundred glyphosate users in IA, IL, IN, MS, NC, and NE were surveyed by researchers to find out exactly how they used glyphosate and the timing of the applications. The dominant use was a burndown application ahead of cotton and soybeans. Between 54% and 63% of farmers used one or two glyphosate applications as a post emergent weed control in either continuous corn or corn and soybean rotations. Up to 62% of Roundup Ready soybeans received a double application, but no more than 42% of Roundup Ready corn received a double application. Only 16% used a non-glyphosate herbicide in Roundup Ready beans. 40% of Roundup Ready cotton received as many as three applications.

In addition to the findings of the telephone survey, researchers created 150 test plots of 25 acres each. The farmer was to use his current herbicide program on half of the plot and the university researchers managed the other half of the plot with a program designed to reduce the potential for glyphosate resistance, and rotate alternative herbicides as needed. The jury is still out on the long term field study.

Of the changes that glyphosate has brought to agriculture, one of the more significant is its impact on tillage practices. The tillage research study found that glyphosate was the reason that the number of no-till increased from 25% to 41%, the number of farmers using reduced tillage increased from 38% to 41%, and 92% of farmers using no-till prior to glyphosate have remained with no-till. Of the farmers using conventional tillage, 25% shifted to no-till and 31% shifted to reduced tillage after adopting glyphosate.

Awareness of the potential herbicide resistance with glyphosate may seem to be widespread, but researchers found that not to be the case in another study. About 30% to 40% of farmers were aware of glyphosate resistant weeds in their state, but no more than 30% believed glyphosate resistance was a serious agronomic issue. While as many as 19% reported some resistance on their farm, no more than 65% had taken any action to minimize the resistance.

The Benchmark Study found that as many as 66% of farmers thought weed pressure declined after switching to glyphosate, but as many as 50% thought it remained the same and some indicated weed pressure increased when all tillage systems were considered.

Most weed species, except for morningglory and pigweed species, present before the introduction of Roundup Ready crops continue to be problematic weeds, but to a reduced degree after adopting Roundup Ready cropping systems.

Summary:
The Benchmark Study on glyphosate found the culture of fighting weeds on the farm had changed, and in some cases there was heavy dependence on glyphosate with little use of alternative herbicides. Glyphosate had allowed many farmers to move their tillage practices away from conventional systems and toward no-till. Awareness of potential glyphosate resistant weeds has gaps, and some farmers believe their weed pressure had not declined after switching to glyphosate.