Apply the right herbicide at the right time to slam the door on resistant weeds and kick up yield

As much as we hate to admit it, stress—within limits—often makes us perform better. Soybeans are the same way. Farm Journal studies have found that inducing stress by spraying soybeans at the proper time with certain herbicides can stimulate higher yields.

The burning technique is gaining interest not only because of high soybean prices but because many growers are using additional herbicides to combat resistance to glyphosate. If the herbicide you add prevents or controls resistant weeds and bumps yield a few bushels, that’s a double payoff.

"At today’s soybean prices, a 3-bu. yield response at $11 or $12 per bushel grosses $33 to $36 per acre," says Farm Journal Field Agronomist Ken Ferrie. "That’s a strong incentive to look at the practice, especially if you’re going to be applying a herbicide anyway."

The concept points out an important difference between soybeans and corn. As Ferrie often says, you never want a corn plant to have a bad day because yield will actually decline. In soybeans, a tough day during the vegetative stage can cause plants to come roaring back.

In the Farm Journal Test Plots from 2001 through 2004, Ferrie found an average yield increase of 2.6 bu. per acre from stressing plants with a herbicide. The increase resulted from more nodes per plant, shorter internodes and fewer aborted beans, he says.

Demonstration plots planted in 2011 by Farm Journal Associate Field Agronomist Missy Bauer produced similar results. She sprayed 10 oz. of Cobra herbicide per acre on soybeans at the V3 vegetative stage.

Alternating sprayed strips are visible one day after application in Farm Journal Associate Field Agronomist Missy Bauer’s herbicide-stress demonstration plot. Three of the four varieties in the plot produced more nodes, pods and soybeans as a result of a well-timed chemical application, which spurred the bean's final growth.

In three out of four trials, the stressed soybeans produced more nodes, pods and beans per plant. The average increase was one more node, 1.4 more pods and 3.8 more beans per plant.

Yield increases aren’t automatic, though. In Ferrie’s plots, there was one year when the yield decreased. "That season, because of the weather, the stress delayed maturity and worked against us," he says. "Stressing soybeans in the vegetative stage delays maturity. Stressing them in the reproductive stage speeds up maturity."

In Bauer’s plots, one of the four varieties produced more nodes, but fewer pods and fewer beans. "That might have been because it was the shortest-maturity variety in the plots, only a 0.8," she says. "While it was in the vegetative stage, it might also have been entering flowering, which would also put it in the reproductive stage. We call this the V3/R1+ stage.

"The other varieties had longer reproductive periods, which gave them time to put pods on the additional nodes that resulted from burning," she adds.

Burning soybeans requires thorough management that begins with herbicide selection.

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