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Zap weeds early for a clean start

Corn yields of 200+ bushels per acre make a corn grower smile from ear to ear. Early weed control, though, could make this smile even wider.

“Folks are tickled when they get corn yields of 210 to 215 bushels per acre. But they could get 240 to 250 bushels if they didn't let weeds attack the crop during the first two to three weeks of the season,” says Gordon Vail, technical brand manager with Syngenta Crop Protection. “Many folks are using the wrong measuring stick when it comes to the impact weed control has on yields.”

Early-season weeds rob yields you cannot see at harvest. A 2008 Iowa State University (ISU) trial found weed competition between the V2 and V4 corn growth stages clipped yields 1.1 bushels per acre per day. Daily losses jumped to 17 bushels per acre when weeds competed with corn between the V4 and V5 stages.

Early weed competition can hurt soybean yields, too. Fortunately, residual preemergence herbicides can nix these weeds. Some of the following changes in herbicides for 2011 will help you better manage weeds. They've been compiled by Mike Owen, ISU Extension weed specialist, and Kevin Bradley, University of Missouri Extension weed specialist.

• Fierce herbicide is a new premix from Valent. It contains flumioxazin (the active ingredient in Valor, Gangster, and Valor XLT) and pyroxasulfone. Also known as KIH-485, pyroxasulfone spent most of the 2000s in testing. Its addition enables the premix to control many annual grasses and small-seeded annual broadleaf weeds. Owen sees it as a residual preemergence fit in soybeans. It also is registered for no-till and reduced tillage corn production and as a fall burndown treatment.

• Prequel is a new premix from DuPont. It contains rimsulfuron (Resolve) and isoxaflutole (Balance Pro). Prequel can be applied up to 30 days prior to planting and has burndown activity on a number of winter annuals and early-emerging summer annual weeds. Prequel also gives residual control of various summer annual grass and broadleaf weeds.

• TripleFlex is a premix from Monsanto. It contains acetochlor (the active ingredient in Harness and others), clopyralid (in Hornet), and flumetsulam (in Hornet). TripleFlex is normally applied at 1.5 to 2 pints per acre, but a supplemental label allows a maximum rate of 3 pints per acre.

• Verdict is a new name for Integrity, part of basf's Kixor stable. This premix contains Sharpen (saflufenacil) and Outlook (dimethenamid-P) in the same ratios as Integrity. Verdict is labeled for preemergence use in corn at 10 to 16 ounces per acre, depending on soil type. Verdict is also labeled for preemergence use in soybeans at 5 ounces per acre. Verdict cannot be applied postemergence to corn.


  • Warrant is an encapsulated acetochlor from Monsanto. It can be applied over the top in soybeans and cotton. It has a supplemental label for field corn. Warrant can be applied in corn from emergence up to a 30-inch height.

Warrant should be applied before weeds emerge, since it has no postemergence activity on emerging weeds. Thus, it needs to be tankmixed with other products that have activity on weeds present at application.


• Authority XL is a new soybean preemergence premix from FMC. It contains Authority (sulfentrazone) and Classic (chlorimuron-ethyl). Authority XL is labeled at foundation rates of 3.2 to 4.5 ounces per acre for use in Roundup Ready or LibertyLink soybeans. Outside of these systems, full-use rates range from 5 to 9.6 ounces per acre. Authority XL offers both burndown and residual activity on a number of broadleaf weeds.

• Ignite, used on LibertyLink crops, has new seasonal maximum rates that have been hiked from 44 to 65 ounces per acre. This allows users to apply 22 to 36 ounces per acre in the first pass and 22 to 29 ounces per acre in a second pass.

• Syngenta has several new premixes and label changes.

Callisto Xtra is labeled for postemergence on several crops including field corn.

Flexstar GT is specifically registered for glyphosate-resistant soybeans. It controls some glyphosate-resistant weed biotypes. A new formulation, Flexstar GT 3.5, is also available.

Peak (prosulfuron) herbicide is now registered for corn. “It has good activity on burcucumber,” says Owen. “This is another one of those boutique weeds that are popping up more frequently than in the past.”

Expansions and replacements

Some compounds for corn and soybeans have been expanded, and others have been discontinued for the 2011 growing season.

Capreno, a corn premix launched by Bayer CropScience in limited areas last year, will now be widely available to farmers in 2011. Capreno contains an ALS inhibitor (thiencarbazone-methyl), an HPPD inhibitor (tembotrione, the active ingredient in Laudis), and a safener (isoxadifen).

Balance Flexx, a Bayer corn herbicide, has replaced Balance Pro. Balance Flexx combines isoxaflutole and a cyprosulfamide safener that extends application from early preplant preemergence up to postemergence V2 applications.

You'll see the new active ingredient pyroxasulfone in a BASF product called Zidua in 2012. Pyroxasulfone will also be included in a FMC premix in 2012, pending regulatory approval. Pyroxasulfone, contained in Valent's Fierce premix for 2011, will be teamed up with FMC's fluthiacet-methyl compound in Anthem herbicide. Company officials say pyroxasulfone gives control of most grass and broadleaf weeds when applied preemergence and early postemergence in crops including corn and soybeans.

Label changes from Syngenta include those for Fusilade DX, which can now be applied postbloom to soybeans and has a 60-day postharvest interval.

Label additions for Prefix include application of Ignite following Prefix applications.

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