When Weed Killers Miss Their Mark

Aug. 31, 2018
Mark Loux will be discussing weed control during the Farm Science Review. Photo by Ken Chamberlain.
COLUMBUS, Ohio — The field appears as a checkerboard: thriving green crops beside squares of shriveling beige stalks.
This was not a farmer’s bad luck. Instead the field was intentionally sprayed with 13 different weed killers to show their effects on various crops as well as the consequences of herbicides that drift from their intended target.
“Would a farmer do this to a field? Absolutely not,” said Harold Watters, an agronomy field specialist with Ohio State University Extension, the outreach arm of the College of Food, Agricultural, and Environmental Sciences (CFAES) at The Ohio State University. 
“The purpose is to share what can happen when things don’t go as planned.”
For farmers, weeds are more and more of a vexing problem as the herbicides that used to kill them no longer work. Just about every year at least one weed in Ohio is shown to survive a herbicide that used to destroy it, Watters said.
The increased use of a herbicide often causes the target weed to become resistant to it, in much the same way that increased use of antibiotics has led to some of them no longer being effective against certain bacterial infections.
At least seven different types of weeds common in Ohio are resistant to one or more herbicides that previously killed them, said Mark Loux, an OSU Extension weed specialist. Waterhemp, one of the more rapidly spreading weeds in Ohio, is particularly troublesome because of its resistance to so many weed killers including glyphosate, a popular herbicide.
Watters and Loux will be among a team of OSU Extension experts who will discuss issues relevant to farmers, including weed killers, cover crops and nutrient management, during the 56th annual Farm Science Review Sept. 18-20 at the Molly Caren Agricultural Center near London, Ohio. The annual agricultural trade show is sponsored by CFAES.
Besides illustrating the effects of various herbicides, the demonstration plots at the Review will show how nutrient levels within a field can differ significantly.
“I can look across a field and see waves of differences,” Watters said.
One portion of a field might be low in phosphorus, while another section has enough of it, information a farmer needs to ensure that no portion of a field is treated with too much of the key nutrient. Those differences underscore the need for a farmer to apply different rates of fertilizer or manure to different parts of a field growing the same crop to prevent the potential for runoff of those nutrients into an above ground water source, Watters said.
Tickets for the Review are $7 online, at participating agribusinesses and county OSU Extension offices, and $10 at the gate. Children 5 and under are free. Hours for the event are 8 a.m. to 5 p.m. Sept. 18-19 and 8 a.m. to 4 p.m. Sept. 20. For more information, visit fsr.osu.edu.
Alayna DeMartini
Mark Loux

Harold Watters