Volume 41, Number 12 | JUNE 9, 2015
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PRACTICAL PRODUCTION TIPS FOR THE PRAIRIE FARMER
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HERBICIDE-RESISTANT WEEDS CHANGING FARM PRACTICES Resistant weeds are driving U.S. farmers to actions like manual weeding By Lisa Guenther
A
glyphosate resistance. Scott said the difference between resistant and susceptible horseweed was like the difference between a Roundup Ready crop and a regular crop. Horseweed seeds are wind-borne, so resistant plants spread rapidly across the state. Scott said the weed also started emerging later in the spring. “So we were selecting for a biotype of this weed that was not only resistant to Roundup, but was emerging after the dicamba went out, after the burndown went out, and coming up in the Roundup Ready crop.” Other glyphosate-resistant weeds — common and giant ragweed, Johnsongrass — followed. Scott said
the state was averaging a new glyphosate-resistant weed every year and a half to two years. “We were throwing something in the tank. We were adding a burn-down. But we really hadn’t made a lot of wholesale changes in the way we farm,” said Scott.
The first signs of resistance In 2006, a farmer reported a Palmer pigweed patch that he’d sprayed several times with glyphosate. “So we came out and sampled some seeds, took them to the greenhouse, and had one of those ‘Oh, crap,’ moments,”
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photo: laura rance
rkansas has been ground zero for herbicide-resistant weeds. For instance, the state is second only to Australia in the amount of herbicide-resistant ryegrass in wheat. “We’re actually running out of herbicides, making it difficult for us to even grow wheat in Arkansas, because of the levels of resistance that we have,” said Dr. Bob Scott. The state has had a large helping of resistance problems in other crops as well. Scott shared Arkansas’ herbicideresistance history with farmers gathered in North Battleford for Cavalier
Agrow’s farm forum. Scott, a weed scientist, works in extension through the University of Arkansas. By the 1990s, Arkansas farmers were already battling weeds that were immune to DNA herbicides. Farmers were also facing other problem weeds such as ALSresistant cockleburs. “In 1999, Roundup came along and rescued us,” said Scott. Farmers rapidly adopted glyphosate, and everything seemed great, he said. “But what we didn’t know at the time was that we were putting an astronomical amount of selection pressure on Roundup as a herbicide,” he said. Horseweed was the first to develop
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In This Issue
Wheat & Chaff .................. 2 Features . ........................... 5 Crop Advisor’s Casebook . 8 Columns ............................ 10 Machinery & Shop............. 14 Cattleman’s Corner .......... 20
ESN simplifies seeding lee hart page 5
New JD round balers
scott garvey page 19
FarmLife ............................ 39