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Published January 30, 2013, 02:10 PM

Advances in spraying

Adjuvant steps up as farmers fight resistance.

By: Mikkel Pates, Agweek

FARGO, N.D. — As farmers gird for a fight against herbicide resistance, guys like Greg Dahl will be behind the scenes, looking to find them new weapons.

Dahl is research manager in product development for WinField Solutions LLC, and Land O’Lakes. A former North Dakota State University Extension Service pesticide specialist, in his private roles he’s done such things as help develop products that include InterLock, WinField’s increasingly popular adjuvant that has become one of the company’s private-label flagship products.

Prior to InterLock, some farmers were using a polymer-type product, which made droplets larger.

In the early 2000s, Dahl and others at Land O’Lakes started testing InterLock, a modified vegetable-oil-based product. The product was brought to them by a supplier, and they looked at it for a number of uses.

“We saw that this product was, in fact, changing the way spray solutions came out of the nozzles,” Dahl says. “We started testing it for drift control. Over the years, we looked at it for canopy penetration and deposition — getting more product to land where we wanted it to land, and farther down into the canopy.”

InterLock came onto the scene for sale in 2004 and had its first major year in 2005, and has increased in sales every year, including 2012. The retail cost varies, but usually is a “nominal” amount depending on market location and other factors. The product use started in Upper Great Plains crops and moved out, and is used on virtually any crop for weed, insect and fungicide application, Dahl says.

Increasing contact

While an adjuvant itself doesn’t kill the weeds, research indicates it increases effective contact of herbicides, insecticide and fungicide products by 10 to 20 percent, or more. While conventional surfactants lower the surface tension of water and herbicide droplets, sometimes creating finer droplets, InterLock works differently.

InterLock has the effect of reducing the number of ineffective, large droplets that can drop to the ground, and reduce the incidence of very small droplets that lose speed and stop falling before they hit the plant, or dry up. “You get more of the optimum ‘middle-sized’ droplets which we are looking for,” Dahl says. “They hit and land and are the ones that do the effective work for you.”

InterLock is applied to about 15 million acres annually in North Dakota, South Dakota and Minnesota, according to company marketers. It is the second-largest in acres for "branded" crop protection products in the United States, behind the Roundup brand of glyphosate.

Dahl has had a front-row seat on the “glyphosate era.”

In the 1990s, weed control was more difficult than it is today. Farmers needed to use several chemistries and weed control programs were complex. Glyphosate (Roundup brand) came in and was used on the soybean, cotton and corn crops. “Weed control became an easy thing to do. You could spray a couple of times and end up with clean fields. You could be flexible on timing,” Dahl says.

Problem solved?

Chemical manufacturing companies backed off on some of their development. “We had, in a lot of cases, solved the problem (of weeds) but then we found out it was only for the time-being.”

In the 1990s, there were some scientists who didn’t think glyphosate resistance in weeds would ever occur, but it did. It started in Australia and exploded across the United States. It started with marestail in many places, and then in cotton with Palmer amaranth. Later, it spread to waterhemp, ragweed and kochia.

“Now everybody is trying to put in place strategies in order to get through this problem and on to whatever our future will be,” Dahl says.

Strategies include weed spray programs that involve multiple applications of multiple herbicides at multiple times. Experts believe farmers will need to use more residual herbicides. There will be more focus on crop rotation, herbicide rotation, and cultural practices such as delayed planting, or planting early so farmers can get the crops harvested early and do some weed control after the crop.

“Another thing would be tank-mixing things so you have more than one product effective at the same time,” Dahl says. “We’re trying to put the proper adjuvant in place to make the herbicides work the best they can.”

The goal will be complete weed control so there are no surviving weeds, including in fencerows and ditches. “And we can’t have off-target movement. We have to keep the product in the field,” Dahl says.

One concern is that while farmers will need to be more diligent at tracking down every weed in the field and in margins, the U.S. Environmental Protection Agency will be developing rules over herbicide labels that would limit their use in buffer zones. “We know pesticide applicators have to follow the label,” Dahl says.

As weed resistance becomes a bigger factor in the Red River Valley and elsewhere, NDSU weed experts are saying farmers need to shoot for 100 percent control. While that may never be attainable, it’s the right goal, Dahl says. “That’s the ideal we’ve got to shoot for and we’ve got to come as close as we can.”

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