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Knock back resistant weeds

Herbicide-resistant weeds may be on their way to your fields. So, what can you do to make sure you don't become another part of the problem?

Turning to different herbicide products is the foremost way to prevent resistance, but a thorough off-season examination of your cultural and managerial practices can have just as much of an effect on your resistance potential in the coming crop year, says one agronomist.

“Growers should attack problem weeds with multiple modes of action and multiple tactics,” DuPont Pioneer agronomy research manager Mark Jeschke says in a company report. “This will control more weeds and preserve effective herbicide technologies longer, giving growers more options."

That starts with making sure you're getting your crop off on the right foot. That means creating a clean seedbed, something that may require early action this spring even if you did put down herbicide last fall to control winter annual weeds.

"While fall herbicide application can help control winter annuals, the value for summer annuals that emerge five or six months after treatment is questionable," according to a report from Pioneer. "A spring pre-emergence herbicide program can help further reduce resistance with a burn-down on the field."

Next, consider your in-season herbicide lineup and the timing and frequency of your applications. Spreading out those applications throughout the year -- versus one time through the field -- can do wonders for the efficacy of whatever broad-spectrum product you may be applying.

"A two-pass system of pre-emergence and post-emergence herbicides is another successful strategy for growers and is particularly effective for controlling broadleaf weeds that emerge early and grow rapidly," according to a Pioneer report. "Split application is another emergence tactic, which boosts control and provides better residual activity to help combat late-season weeds."

But, if you're taking 2 trips across the field instead of just one, that shouldn't be reason to cut back on prescribed rates, adds Jeschke. "When using a pre-emergence program, growers should use the full rates recommended for these weeds," he says. "A good, broad-spectrum burn-down will clear vegetation and provide good residual activity to ensure weed control through planting.”

Another tactic to manage weed herbicide resistance is in adjusting post-emergence applications. By bumping them up earlier -- to when weeds are closer to 3-5 inches in height -- Jeschke says control can take hold during a key growth stage for most weeds, an important measure for overall herbicide efficacy.

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