To reduce the amount of herbicide injury in soybean, says Tom Eubank, growers should “stop chasing the planter with the spray rig, and instead chase the spray rig with the planter.”

While soybean growers have a roster of effective residual herbicides for use against Palmer amaranth (pigweed), he says, they should be aware that crop injury can occur.

 “We’ve got to have residual herbicides to manage our weeds,” he said at the annual meeting of the Mississippi Agricultural Consultants Association, “and we may have to accept some level of crop injury as a necessity in order to get the benefits that come from using these products. But we can significantly reduce this injury potential by changing the timing of these applications.”

Eubank, assistant Extension and research professor at the Delta Research and Extension Center, Stoneville, Miss., said the 2013 crop year is a good example of the injury scenario.

“We had an almost perfect storm: We’d get a rainfall event, then run out into the field to plant and spray; then we’d get a rain, and we’d repeat the process. As a result, we had a lot of fields with a lot of injury from several different herbicides.”

 

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Making a herbicide application after the planter has already gone through the field often involves “a very narrow window of opportunity, especially when temperatures are warm,” Eubank says.

“You might only have two or three days before soybeans start cracking the soil surface, and if there are weather delays, you may not be able to apply these residual herbicides prior to soybean emergence. Then, you’re forced to use postemergence materials earlier in the season than is really warranted — or worse, you may not be able to get them out at all.

“The approach I advocate is for the planter to chase the sprayer, and where farmers used this approach last year, they didn’t have nearly the injury issues we saw when we were making an application behind the planter.

“I would prefer to apply these herbicides seven to 10 days prior to planting, when we have a combination of things working for us. One, we’ve got much less injury potential — if the herbicide gets incorporated before the beans come up, we’re less likely to see injury occur. Two, our window of application is much wider.