Weed Experts: Aggressive Management a Necessity for Resistant Weeds

By Jim Steadman



Speaking at the recent MANA Southern Crop Consultant Meeting in Memphis, Alan York, professor emeritus at North Carolina State University, warned an audience of Mid-South crop consultants to have programs in place now to deal with herbicide-resistant weeds, especially Palmer amaranth.

“We have about a five-year head start on you folks here in the Mid-South,” he noted. “If you haven’t decided yet that Palmer is going to change your life, sit tight. You will soon decide.”

In cotton, stated York, control requires multiple applications before, at and after planting, including use of residual herbicides at each step. He recommends an aggressive program beginning at burndown.

“We tell our growers, when you leave the field with the planter, you’d better have 100 percent control,” he pointed out. “You have to start even.”

Growers should start with an early burndown treatment, including a residual herbicide for initial control, followed by a second burndown – also with a residual – at planting. “This way, if I don’t get any rain behind the planter, I still have something working for me in the field,” said York.”

The first post application of Roundup or Liberty – depending on the cotton variety – should come 14 days after planting, followed 14-to-18 days later with a second post application. Both post applications should include residual herbicides. A residual lay-by application should go out 14-to-21 days after the second post treatment.

“The goal is to overlap residuals,” emphasized York, “and timeliness is important. If we want to catch Palmer when it’s small enough to deal with, that’s the kind of calendar we’re on.

“So far, I think our growers have done an outstanding job,” he continued, “not necessarily because they wanted to, but rather they had to. It’s been painful and it’s been expensive. But we’re making progress.”

Hand weeding has also become more common in managing resistant weeds, especially Palmer amaranth, and that factors into the overall cost of a management program. “Our weed control costs have tripled because of that one weed,” reported York.

York said that a new zero tolerance initiative – WeedFreeNC – is now beginning in North Carolina to help draw attention to the need to reduce the overall seed bank of weeds throughout the state.

“This year, we know cotton acres are going to be down, not because cotton prices are bad, but because prices for other crops are better,” said York. “I’m telling our growers not to sit on this problem. We have good programs for corn and soybeans, so let’s work on them and continue to try to reduce that seed bank.

“Because when we get that year – which is coming – where we get 20 bushels of beans and 30 bushels of corn and remember why we were planting cotton to start with, we’ll have a head start on this weed.”

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