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Safener solutions

THE DAYS when corn growers would tolerate a little crop injury from herbicides in return for excellent weed control are long gone. Increased production costs — especially seed costs — combined with the efficacy and cost-efficiency of glyphosate, have raised the bar on crop safety and even the cosmetic appearance of a corn crop.

Members of the crop protection industry have responded to growers' increased demands for safety by developing new safener technology that provides a margin of plant protection not available — at least in postemergence herbicides — before now.

Two new safeners

The two most recent examples are isoxadifen and cyprosulfamide, new safeners developed by Bayer CropScience. When added to herbicides, these compounds contribute to corn safety by enhancing herbicide selectivity and increasing the speed at which plant enzymes metabolize herbicides into nontoxic substances. This increased selectivity may allow the herbicide to be used in ways that improve performance, such as at higher use rates or with greater flexibility in application timing.

“Bayer's isoxadifen is very flexible,” notes Bob Hartzler, Iowa State University weed scientist. “BASF has licensed it and has put it in their dicamba product, Status. DuPont is also using it in several of their sulfonylurea herbicides: Accent Q, Resolve Q and Steadfast Q.”

The crop protection industry, which has offered preemergence herbicides with safeners since the 1970s, now focuses its efforts on safening those herbicides that can better complement or compete with glyphosate. An added benefit for growers, in many cases, is that the cost efficiencies of using glyphosate have helped keep prices fairly flat for these new and refurbished products.

Resolve Q, introduced in 2008, was designed to provide growers with contact plus residual control of tough grass and broadleaf weeds in a glyphosate-tolerant corn program, says Jeff Carpenter, U.S. corn portfolio manager for DuPont Crop Protection.

He says that the addition of isoxadifen enables growers to use Resolve Q under more diverse conditions. “Growers are able to increase the adjuvant load with these products and run with crop oil or even MSO, because of the safener,” Carpenter says. “That results in better coverage and better activity.”

BASF introduced Status, which contains isoxadifen, in 2007. The company says the broadleaf herbicide can be used as a stand-alone product or as a tankmix partner for glyphosate.

Bayer includes isoxadifen in several of its new herbicides, including Laudis, which was introduced to corn growers two years ago, and Capreno, which will have a limited launch in Michigan, Minnesota and Wisconsin this year, with a full market introduction expected in 2011. Bayer says Capreno offers multiple modes of action for season-long grass and broadleaf weed control.

Cyprosulfamide, which Bayer refers to as its crop safety innovation (CSI) safener, is used in Balance Flexx (a new formulation of Balance Pro) and Corvus, introduced in 2009 for broadleaf weed control.

Cyprosulfamide works with the plant systemically, through both soil and foliar uptake, to increase the rate of metabolic activity, according to Jeff Springsteen, Bayer CropScience corn and soybean marketing manager. “That provides a high level of safety for the plants as the herbicide works,” Springsteen says. “It also increases the flexibility of application timing, compatibility over various soil types and maximizes root growth and plant health.”

Isoxadifen provides foliar protection only.

Crop injury

University of Illinois weed scientist Aaron Hager says that, although safened herbicides are valuable to the industry, that doesn't mean growers should apply them and then forget about them. “It'd be unnerving to me to tell a farmer that he actually has no worries about crop injury occurring now with safened herbicides,” Hager says. “The important message for farmers to take away is that vigilant scouting should still occur in their fields.”

Essentially, whenever corn growers do see crop injury from a herbicide in their fields, it occurs because the plant's metabolism wasn't able to work adequately or fast enough to break down the herbicide, Hartzler explains. He says that, other than adverse weather, misapplication or off-label use of a herbicide contributes most often to crop damage.

Both isoxadifen and cyprosulfamide extend the window of application for corn herbicides, in some cases by eight to 12 days. This allows growers the flexibility of using many of the newer and refurbished herbicides in a preemergence application or even for early postemergence weed control.

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