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Take A Stand Against Resistance

Starting clean the first step in fighting resistance.

Tyler Harris

May 18, 2014

5 Min Read

Back when Syngenta's Resistance Fighter of the Year Leadership Program started in 2009, Dr. Jason Weirich, director of agronomy at MFA, Inc. in Columbia was earning his PhD in Weed Science at Mississippi State University. Even then, he says, glyphosate-resistant weeds were a problem in Missouri.

Weirich, a 2013 Syngenta Resistance Fighter of the Year, says now, it's everywhere – in Palmer amaranth, waterhemp, giant and common ragweed, and marestail. "We're starting to see a lot more issues pop up as far north as we go," he says. "I would say 70% 80% of the acres MFA covers have at least one glyphosate-resistant weed on that farm, and I think the trend is picking up as far north as we go."


RESISTANCE FIGHTER: Jeremy Valentine (left), retail business representative at Syngenta, hands Dr. Jason Weirich a plaque honoring him as a 2013 Syngenta Resistance Fighter of the Year for his role as a leader and mentoring growers in the fight against resistant weeds

According to Dr. Les Glasgow, Syngenta herbicide technical product lead, estimating yield loss due to resistance is difficult, but some university studies have been able to with competitive weeds. Research at Oklahoma State University demonstrated eight Palmer amaranth plants per 3.35 feet of row reduced cotton lint yield by 92%. Purdue University found competition from waterhemp reduced soybean yield by 44%, and Ohio State demonstrated two giant ragweed plants per 110 square feet reduced corn yield by up to 13%.

"The cost of resistance to the grower can be significant, with an increase of up to $20 or more per acre for additional herbicides and up to $100 per acre for hand weeding, where suitable herbicides are unavailable," Glasgow says.


In Weirich's area, which includes Missouri, southern Iowa, northern Arkansas, and eastern Kansas, continuous soybean farmers that have been no-tilling 15 to 20 years are at the greatest risk for resistance. Due to how easily resistance can spread via seed attached to machinery, even fields rotating between corn and soybeans are at risk.

Start clean
The first step in fighting resistance is starting clean, Weirich says. This means using a pre-emergent residual herbicide at the full rate. "The best way to control weeds is never see them," he says. Planting into a field where weeds have already emerged can spell trouble – if injured by a planter or tillage in spring, a defense mechanism closes them off to chemicals. "Take marestail, for example. If I nick those roots with my planter, I might as well name that marestail, because it's going to be there all year."

Following a pre-emergent residual, Weirich recommends coming back 30 to 45 days later with an overlapping residual, creating a two-pass system and extending protection into the growing season. A single pass may seem appealing to the wallet, but he says growers usually pay for it later. "Growers will spend $15, $20, or $30 an acre on a pre, but they don't want to come back with that planned two-pass program at 30 days, and a lot of times they're willing to spend $55 or $60 on a salvage treatment at R1 trying to salvage the soybean crop at that point."

It's important to have not just multiple modes of action, but multiple effective modes of action, especially for soybeans, Weirich says. "The pre-emerge herbicides we're putting out – Authority, Valor, Sonic – those are all solely relying on PPO chemistry," he says. Options for second passes include Warrant or Dual Magnum, VFLA inhibitors, instead of two passes of PPO-inhibitors. "Over the top of soybeans we're relying on Flexstar and Cobra. Those are also PPOs, so we're putting a lot of pressure on PPOs."


Some no-till farmers may be thinking about bringing out their old moldboard plows. Although there are some situations where tillage can be beneficial for weed control, Weirich doesn't recommend compromising soil health. "I believe we have the tools, with Gramoxone, Sencor, 2,4D, Dicamba, those types of burndown products to be able to start clean without the use of tillage."

Coming down the pipeline
Weirich notes the landscape is changing. Pending EPA approval, Dicamba, 2,4D, and HPPD tolerant soybeans will be available in the next few years. Weirich and MFA have been educating employees and growers on technology coming down the pipeline. With new technology, it's important for growers to keep records of what variety is planted where, and to keep applicators educated on potential for drift, volatilization, and tank contamination.

In 2012, MFA started its Training Camp program, bringing field staff from its 150 retail locations to an 18-acre site near Boonville. In 2012, 330 people attended, and in 2013, 438 attended. "We send out seven buses and they just pick up people along the way," Weirich says. "It's a pretty cool sight to see. Our company has 1,600 people full time, and we had 438 of them there at one time for agronomy training [in 2013]."

The half-day of training covers everything from fertility, new varieties, nozzle tip demonstrations, herbicide symptomology training, and of course, fighting resistance and educating younger generations on new technology and older alternatives to glyphosate.

"If I go back to '96, '97, '98 when RoundUp Ready crops were introduced, there was a rapid adoption of it, so we've been using glyphosate for the past 15 or 16 years. Glyphosate is all we know anymore," he adds. "Our generation has basically missed out on the old technologies, the herbicides that we're now using again. We're trying to educate the new generation on the herbicides we're using again."

About the Author(s)

Tyler Harris

Editor, Wallaces Farmer

Tyler Harris is the editor for Wallaces Farmer. He started at Farm Progress as a field editor, covering Missouri, Kansas and Iowa. Before joining Farm Progress, Tyler got his feet wet covering agriculture and rural issues while attending the University of Iowa, taking any chance he could to get outside the city limits and get on to the farm. This included working for Kalona News, south of Iowa City in the town of Kalona, followed by an internship at Wallaces Farmer in Des Moines after graduation.

Coming from a farm family in southwest Iowa, Tyler is largely interested in how issues impact people at the producer level. True to the reason he started reporting, he loves getting out of town and meeting with producers on the farm, which also gives him a firsthand look at how agriculture and urban interact.

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