It's enticing to hit the "easy button" when it comes to weed control. Most farmers did just that when glyphosate came on the scene, not understanding the full ramifications of resistant weeds.
Did growers learn something, or are we headed for this cycle to repeat? For 2020, growers will have not one, but three, effective soybean post platform weed control options -- Enlist E3™ (with 2, 4-D choline, glyphosate and glufosinate tolerance), Beck's Freedom Plus™ (with tolerance to glyphosate and Liberty® herbicides through the LibertyLink® GT27 trait stack), and Roundup Ready 2 Xtend® (with tolerance to glyphosate and dicamba).
"All three post options are very effective across a broad spectrum of weeds," says Joe Bolte, a Beck's Hybrids Practical Farm Research (PFR) Herbicide Specialist/Operator based in Effingham, Illinois. "However," he warns, "relying on one entirely for your weed control is a trap that will take you down the same road to weed resistance as before."
Instead of hitting the "easy button," Bolte encourages farmers to build on the lessons learned fighting weed resistance in recent years and take a new approach. It requires farmers to change the way they think about -- and use -- soybean post herbicides. "Your post trip should be for cleaning up the few weeds that 'broke' with the pre-emergence herbicide application, not to clean up a train wreck," says Bolte.
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Rather than focus on the post application, he advises concentrating on your pre-emergence program. "It all begins with starting clean. You want to use a good burndown so you're not planting into a carpet of weeds."
Bolte recommends selecting a burndown with a site of action you typically don't use all year. "Sometimes you don't have that flexibility," he concedes, "and maybe you'll have to use a product from the same herbicide group. However, definitely don't use the same active ingredient you'll be using later in the crop season."
The next step is to start strong with a solid pre-emergence herbicide application effective for the weeds on your farm. Bolte's advice:
Use pre-emergence herbicides with multiple sites of action. "Our research has shown that going from using one site of action to two sites of action, we see a roughly 30 percent increase in visual control of waterhemp at 45 days after treatment," says Bolte. "And if we go from one site of action to three sites of action, we see up to a 40 percent increase in control."
Rotate pre-emergence herbicides. "If you have a pre-emergence product that's working very well, use it two or three years, but then switch to a different product making sure that in addition to changing trade names you're also changing herbicide groups. That way," says Bolte, "you're not relying on the same groups to do the heavy lifting in your soybean pre-emergence program."
LENGTHEN WEED CONTROL
Application timing is important. "All we're trying to do with the pre-emergence program is to buy time controlling weeds until crop canopy closure," says Bolte. "Most pre-emergence residual products will break down in three to five weeks, depending on the product and weather. So, the closer to planting you can apply the pre-emergence residual (according to label), the further you can extend weed control into the growing season."
That's important because you want pre-emergence weed control to hold long enough to be able to apply the postemergence application before weeds grow too tall for effective control. "The main thing with all three of the post herbicide platforms is to spray weeds when they're less than four inches tall," says Bolte. "The post application trip, with the addition of an in-season residual, then hopefully buys you another four weeks of weed control to get the soybean crop to canopy closure."
While Bolte sees all three of the post herbicide platforms as effective, he notes that Engenia and XtendiMax herbicides in the Roundup Ready 2 Xtend platform offer a residual soil activity component the other two platforms don't.
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