Crop consultant Bryan Cook
Farmers urged to revisit older herbicides
Nelson Zandbergen
Farmers Forum
CHESTERVILLE — Old-school herbicides are returning to prominence as weeds grow more resistant to glyphosate. Speaking candidly about the challenges of modern weed control to a gathering of farmers in Chesterville, crop consultant Bryan Cook highlighted the reliability of decades-old chemistry in maintaining clean fields.
“We’re using 40-year-old chemistry, most of it, and we still get great weed control,” Cook told the audience, noting the effectiveness of these pre-emergence products — applied to the ground before a crop sprouts — like Dual and Sencor. He noted that the underlying technology dates back as far as 1945 but remains valuable, especially in wet conditions that activate the older chemicals’ residual properties in the soil. They particularly proved their value in last year’s wet May conditions, he said.
Cook explained that the dominance of glyphosate, in concert with glyphosate-tolerant ‘Roundup Ready’ crops that debuted in the mid-1990s, led farmers to rely heavily on post-emergence applications, sidelining residual herbicides. The “cheap and easy” Roundup system was “great,” he said wistfully. Glyphosate’s time is “getting short now,” he added, “but it was fun.”
With weeds like waterhemp and fleabane resistant to glyphosate — as well as troublesome volunteer corn with Roundup Ready genes popping up in soybean fields — he urged a shift back to pre-emergence herbicide strategies. He noted Sencor and Eragon as effective options for soybeans.
He recounted how the industry’s shift to the Roundup Ready model, combined with a consolidation of herbicide companies, wound up curtailing the development of traditional pre-emergence chemicals. Companies put their money into fungicide development instead, which yielded good products on that front. But as a consequence, 30 years have passed since a pre-emergence herbicide came out with a new line of attack — or “mode of action” — against weed biology. Most of the modes of action still deployed in pre-emergence herbicides today were otherwise developed between 1970 to 1990, Cook said.
