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Glyphosate-resistant Palmer amaranth is a predicament that could have been avoided “if we hadn’t used only glyphosate year after year after year,” says Evansville, Ind., farmer Joe Steinkamp, a director of the Indiana Soybean Alliance.
Steinkamp is battling the resistant weed on his farm, where it arrived with floodwaters. To stay ahead of this aggressive species, he’s spending three times as much money on soybean weed control as he did three years ago.
He says adopting an integrated weed management program that deploys multiple effective modes of action “is our duty, not only to protect our livelihood today, but for the future.”
Stick with the plan
Steinkamp’s strategy worked well in 2012, despite just 0.15 in. of June rainfall for herbicide activation — with one exception. “One field gave us fits, and that was a field where we deviated from the plan.”
About a month after planting, the field looked clean enough to skip the postemerge application, “but that wasn’t the case.” By the time Steinkamp realized his mistake, “the Palmer was knee-high” — much too big to kill with any herbicide. So out came the hoes again.
Postemerge herbicides work best when Palmer plants are no more than 3 inches tall, Sprague says. That makes application timing a challenge, because the weed grows so fast. In 2012, Palmer amaranth in Sprague’s research plots “grew from 3 to 7 inches in fewer than 5 days.”
The good news is that “in the Midwest, we can control Palmer amaranth in soybeans and corn with the herbicides we have available today,” Steinkamp says — “as long as we have a good plan and stick to it.”