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 Finally, A Broadleaf Herbicide for No-Till February 2000 Over the past couple decades, the most commonly mentioned obstacle to the production of sunflower fields under a conservation tillage system has been the absence of appropriate EPA-approved pre- or post-emergence broadleaf herbicides. The postemergence grass herbicide "Poast" has been available to sunflower producers for a number of years, as has "Prowl," one of the preplant dinitroanilines that work on both grassy weeds and several prominent broadleaves. Prowl can be used in a no-till scheme since it doesn't require mechanical incorporation. In those instances, one relies instead on sufficient rainfall within seven to 10 days of application to incorporate the chemical. The problem? Those areas where interest in minimum- or no-till sunflower is highest typically are, as well, locations where the odds of receiving a timely spring rain are mediocre to poor. Recent years' university research in North Dakota and Kansas has revealed several promising pre- and post-emergence herbicides for sunflower. But chemical company interest in labeling these products for sunflower has been tempered by the cost of registration in comparison to the perceived size of the market. Finally, however, a herbicide option for sunflower under conservation tillage emerged in 1999. Through efforts of the National Sunflower Association and state university personnel, FMC Corporation's Spartan® gained Section 18 registration for use on sunflower in eight states: Minnesota, North Dakota, South Dakota, Colorado, Kansas, Nebraska, Wyoming and Montana. The need for a Section 18 sunflower label for Spartan was based "on widespread kochia infestations and the lack of adequate products for weed control in conservation tillage programs," FMC noted at the time. Though most interest in Spartan has been as a pre-emergence application, it also is labeled as a preplant incorporated treat-ment on sunflower. Spartan does require precipitation for activation. At a cost of nearly $15 an acre at the medium 4.25-ounce label rate, the price of Spartan (which was originally developed to control weeds in tobacco) deterred a number of sunflower growers from using it last year. FMC has since announced a significant price reduction for the 2000 season, however. Steve Scott is one of numerous producers around the eight-state region who did use Spartan on their sunflower crop in 1999. Scott, who farms south of Burlington, Colo., planned to put sunflower on a 300-acre field that had been in dryland corn the prior season. "But no-till 'flowers hadn't been working for us because of the [lack of labeled pre- or post-] herbicides," he indicates. So at the last moment, Scott decided to work down the standing corn stalks in order to apply and mechanically incorporate Prowl. Ironically, however, rains delayed the tillage operation - and before the field had a chance to dry out, he heard that Spartan had just received a Section 18 in Colorado. Scott immediately changed his plans, opting to keep the field in no-till and use Spartan. First, though, he put on a preplant application of two pints of Gramoxone Extra "with lots of surfactant" to kill emerged weeds - particularly kochia, some of which were six to eight inches tall by this late May date. The sunflower was planted the following day. The Spartan went on several days later at the 4.25-ounce rate, along with 23 gallons of 32-percent nitrogen carrier solution (Scott's basic source of applied N). Though some High Plains sunflower producers reported crop injury from Spartan, Scott saw none on his acreage. He says the herbicide provided very good broadleaf control; not surprisingly, though, it was only fair at best on the grass populations. What have been the experiences of university weed researchers in their investigations with Spartan on sunflower? North Dakota State University extension weed specialist Richard Zollinger says his trials have reflected excellent control of broadleaves (e.g., kochia, pigweed, lambsquarter, Russian thistle). Zollinger also reports suppression of mustard, cocklebur, ragweed and the foxtails. The effective residual control period, he notes, has been six to eight weeks. Phil Stahlman, weed scientist at Kansas State University's research station at Hays, participated in a four-state, seven-location High Plains Spartan project in 1999. All were no-till sites, with the sunflower planted into wheat stubble. Stahlman reports excellent (virtually 100-percent) control of kochia, Russian thistle and redroot pigweed. Similarly to grower experiences in the region, the multi-state study results reflected the need to add a product like Prowl to achieve satis-factory control of foxtail, stinkgrass and other problem grasses. Most incidences of sunflower crop injury from Spartan appear to be associated with either soil texture, soil organic matter content, soil pH and/or the timing of application, according to the university weed scientists. Though Zollinger documented very good sunflower crop safety with Spartan, NDSU's weed control recommendations do caution growers that "temporary sunflower injury may occur in coarse, low organic matter soils with pH greater than 8.0." In the seven-site High Plains tests, two sites displayed significant crop injury as of 30 days after application. By 60 days, however, the sunflower plants had largely recovered and there was no impact on final yields. Stand reduction was observed only when Spartan was applied at higher-than-recommended rates. As in North Dakota, High Plains weed scientists say the risk of crop injury with Spartan is greater on high-pH (over 8.0) and low-organic soils. Other Kansas State University research has indicated that sunflower on soils with high levels of calcium (over 5,000 ppm) also tends to be at more risk of injury from Spartan. Typical injury symptoms included chlorosis, a "rippling" effect on some leaves, and stunting. However, none of those effects translated into lower crop yields as of harvest in the university trials. It appears all eight sunflower states will have another Section 18 label for Spartan on sunflower again in 2000. A Section 3 full federal label is being sought, and it is hoped it will be available for the 2001 crop season. - Don Lilleboe  Back to Weeds Stories Back to Archive Categories
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