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Weed control means effectively using a variety of herbicides in well-managed program

Written by Saige Albert

Worland – Gustavo Sbatella of the University of Wyoming Powell Research and Extension Center said that managing weeds in row crops can be a challenge, and producers focus a lot of energy on avoiding weeds in their crops.

“We pay so much attention to weeds because they compete with our crop for a lot of things – water, nutrients and light,” Sbatella said. “We pay through competition primarily from yield loss, but we might also sacrifice quality. Depending on the crop, the presence of a weed might cause a shipment of our crop to get rejected.”

At the same time, even more detrimental is that the presence of large amounts of weed in a crop may cause custom harvesters to decide not to harvest.

“Custom harvesters don’t want to harvest a field full of weeds because it can be rough on equipment,” Sbatella said.

He continued, “Weeds are hosts of insects and diseases, either for this crop or the one we’re going to be planting next year.”

During his session at the 2017 WESTI Ag Days, held in Worland Feb. 14-15, Sbatella emphasized, “There are a lot of reasons to control weeds.”

Herbicide resistance

Sbatella mentioned, “The importance of weed control is that we have some weeds that are harder to control than others.”

The idea of controlling difficult weeds leads directly to the concern of herbicide resistance.

“We need to start thinking about and approaching herbicide resistance in a different manner,” Sbatella commented. “We have to take into account how resistance fits into our continued weed control programs in a way that helps us to delay resistance.”

“We don’t talk about avoiding resistance anymore,” he added. “We talk about delaying.”

To delay herbicide resistance, Sbatella noted that producers must apply different selection pressure to weed populations by diversifying the mode of action used.

Mode of action

As kochia and other plants become more difficult to control as a result of herbicide resistance, varying the mode of action from herbicides used can help to alleviate weed pressure.

“There are five different modes of action that we can find to use in barley, for example,” Sbatella said, using barley as his example crop. “We have five different modes of action, but in reality, we only have four because all of our kochia is resistant to ALS inhibitors.”

When choosing products, though, Sbatella cautioned producers against simply utilizing the same mode of action repeatedly.

“Chemical companies like to shuffle active ingredients and re-name products, but that doesn’t mean it’s a new mode of action,” he said. “For example, Affinity and Spectrum have a combination of active ingredients, but they’re all in the same group.”

Producers should be careful to make sure they’re utilizing effective products that kill weeds in different ways to be effective.

Strategies

Sbatella noted that 10 years ago, if producers had asked whether using one herbicide one year, another the second and returning back to the first herbicide in the third year was an effective way to manage for herbicide resistance, he would have agreed.

“That sounds reasonable to me, but there are a lot of studies now that provide other information,” he said. “We end up having the same resistances as if we would have used the same herbicide every year.”

“The way to go is using a mixture in our tanks,” Sbatella added. “We should use two modes of action in one application tank.”

He re-emphasized that just using two different herbicides, however, is not enough. Producers must utilize herbicide with different modes of action.

“We’ve got to make sure they’re both doing a good job on the weed we want to control, too,” he said.

For example, if herbicide A controls 99 percent of kochia, it’s going to do well for several years, but the control is going to be reduced if it is perpetually sprayed. However, if producers add herbicide B, which has a different mode of action but only 40 percent control of kochia, he said the population of resistance kochia may actually increase.

“The problem is, that one percent that is surviving won’t be killed with the product that is 40 percent effective,” he said. “The second component isn’t doing anything for us.”

However using a herbicide with 99 percent efficacy paired with one that has 90 percent efficacy is more likely to result in more complete control of the weed.

Control efforts

“When we look at weed control, we have to step back and, instead of just concentrating on the crop that’s in the field today, look at it as part of a crop rotation,” Sbatella said.

When selecting herbicides, Sbatella noted that producers must be cognizant about the next crop in their rotation to assure that they aren’t harming future crops.

“Sometimes producers are very creative and come up with great ways to kill a weed this year, but first, we need to make sure we don’t have a brilliant combination that will beat the living hell out of the next crop,” he said. “We also have to look at crop safety.”

He encouraged producers to look at the impacts of the next crop, such as sugarbeets or dry beans, to assure damage doesn’t happen this year or in the future.

Saige Albert is managing editor of the Wyoming Livestock Roundup and can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it..