To achieve optimum weed control, scouting doesn’t end after the last postemergence herbicide application. Spotting and mapping late-season weeds is a critical step in evaluating this year’s herbicide plan and planning for next year.

Scouting has been a valuable management tool for Terry Ryan, who farms with son Bob and brother-in-law Tom Reilly near Ryan, Iowa. “Tom runs the combine and always makes notes about weed escapes and late-season flushes,” says Terry. “We try to figure out if they’re due to an application glitch because of a manure application or something else.”

Fall tillage is an important element of the operation’s weed-control plan, allowing them the luxury of using only postemergence herbicides on corn and soybeans until now.

“We’ve always been able to get very good weed control by applying full herbicide rates and using multiple modes of action, but over the last few years horseweed (marestail) has become more challenging to control,” he says. “We’re looking at using a preemergence herbicide application next season to widen our herbicide rotation options, as well as to accommodate split-nitrogen application.”

Strategy shift for better weed control
Like Terry Ryan, many farmers have been adjusting their weed-control plans to address the most challenging weed species, including waterhemp, marestail and ragweed, says Ryan Meisgeier, technical sales agronomist, DuPont Crop Protection. “This year, there were plenty of soybean fields with slow crop development, and we saw waterhemp get ahead of the crop before it could canopy.”

Many growers had a targeted preplant or preemergence herbicide control plan, “but then the weather interfered,” notes Meisgeier. “For some, wet fields delayed planting and timely herbicide application. For others, a dry June impacted herbicide activation.”

For Devon Murray, farming with his father and uncle near Charles City, planting and preemergence herbicide application timing were nearly perfect this year. “We’ve been battling waterhemp for years, and every year it seems to get harder to control,” he says. “But this year we were able to get our corn planted in mid-April and the soybeans in May, with rains after both preemergence applications. As a result, we were very happy with our weed control, even on waterhemp.”

2-pass herbicide application works
The Murrays employed a two-pass herbicide strategy with four modes of action on corn acres by using a preemergence application of DuPont Breakfree NXT Lite herbicide, followed by a postemergence tank-mix application of Realm Q herbicide plus Abundit Edge herbicide. “We always follow the labeled rates and application timing and get good results,” says Murray, who handles the applications. “I lean toward applying early since I’d rather control a 1-inch weed than a 6-inch weed.”

Weed control experts agree with Murray’s philosophy. Most herbicide recommendations call for making applications before weeds exceed 4 inches in height or width for best control.

A two-pass program is more weatherproof, too, says Meisgeier. “This spring, growers who made burndown or early preplant herbicide applications had more consistent weed control and more flexibility in timing their postemergence passes. Fields without a burndown or preplant application tended to have more midseason weed pressure.”

Fall weed control strategies to consider
Murray regularly walks fields to keep tabs on what’s going on until harvest, but this year he’s using a drone to scout for uncontrolled and late-emerging weeds. “We’ll map them in the fields and use that information to figure out our best weed-control options for each field next season,” he says.

Where there are weed escapes, Meisgeier recommends prioritizing the harvest schedule to avoid transporting weed seeds to other fields. “Harvest the cleanest fields first and the weediest fields last. That’s especially important if you’re dealing with waterhemp, which can produce more than 1 million seeds per plant,” he says.

Making a postharvest herbicide application is another option to control late-season weeds and prevent weed-seed production, he adds. Combining an economical fall burndown treatment for late-emerged weeds with a residual herbicide delivers cleaner fields in the spring, which often allows earlier planting and reduces the spring workload.

“We make most of our input decisions in December,” says Murray, “and we take advantage of the DuPont TruChoice program to get the most for our input dollars, while still having flexibility to choose the crop protection products we need.”

The TruChoice Early Pay Multiplier helps growers multiply their crop input investment when they make an early budget commitment, says Meisgeier. They can choose specific products as the season unfolds. Details are at earlypay.dupont.com. Local DuPont agronomists can help you review your 2017 weed management and plan for the 2018 season.

Source: DuPont Crop Protection