Granules in No-Till Sunflower
Is there a place for Treflan or Sonalan granules in a no-till sunflower field? The answer seems to be, “Yes, if conditions are right.” Those “right conditions” include an adequate time interval between applica-tion of the granules and sunflower planting, relatively cool temperatures while they’re lying on the surface, and significant rainfall or melting snow to incorporate them.
The lack of herbicide options has always been an obstacle for farmers raising sunflower within a no-till system. For years, trifluralin (Treflan) and ethalfluralin (Sonalan) granules have been widely applied and mechanically incorporated in conventional sunflower programs, and there’s also a supplemental label for Sonalan 10G on sunflower via reduced-tillage (V-blade) incorporation.
Within recent years, however, research in both Canada and the United States has been looking at the feasibility of using surface applications of trifluralin and ethalfluralin for control of grasses and broadleaves in sunflower or other oilseeds. Results to date suggest that while not always as consistent as the control from a mechanically incorporated treatment, surface applications can work well if enough precipitation is present during the appro-priate period for activation of the granules.
The practice is not currently recommended by DowElanco, the manufac-turer of Treflan and Sonalan; nor is it listed on the product labels. So if a sunflower grower does opt for a surface application and weed control proves unsatisfactory, the company has no obligation to stand behind its products when applied in this manner. As long as the application rate does not exceed the high-end rate listed on the product labels, however, such a method of applica-tion would not be illegal.
Kansas State University researchers are conducting a third year of experiments in 1996 to assess the effectiveness of spring-applied Treflan TR-10 and Sonalan 10G in no-till sunflower situations. In both 1994 and 1995, the surface treatments were applied in early spring (end of March/first of April), with April and May rainfall serving as the incorporation mechanism.
Weed control specialist Phil Stahlman reports that 1994 test results from the KSU Agricultural Research Center at Hays were generally good. Treflan TR-10 at rates of 1.0 and 1.25 pounds active ingredient per acre and Sonalan 10G at 1.0 pound ai/A provided 75 percent or greater control of green foxtail, stinkgrass, redroot pigweed and tumble pigweed, compared to little or no control from surface-applied liquid formulations of these products. The TR-10 treatment was slightly more effective than were Sonalan granules at Hays that season.
The 1995 test results at Hays were skewed by what was the driest summer on record and correspondingly low weed populations. However, sufficient spring moisture provided good activation of the granules and excellent weed control compared to liquid treatments.
Results at Tribune — about 150 miles southwest of Hays — were less positive in 1995. “Their major problems are kochia and Russian thistle, and we did not do a good job in controlling those weeds with any of our treatments at Tribune,” Stahlman notes. Though he’s awaiting the 1996 results from both Tribune and Hays, his preliminary conclusion is that the granular surface treatments have a “niche fit” in no-till sunflower where the main weed problems consist of grasses; but they may not be as feasible in areas where certain broadleaves — particularly kochia — are particularly troublesome.
A complication with counting on the trifluralin or ethalfluralin granules, according to the KSU agronomist, is that a major weed in many Kansas sunflower fields is volunteer wheat from the preceding winter wheat crop. “That has serious implications, more so from a disease standpoint than a competitive one,” Stahlman notes, “since volunteer wheat serves as the reservoir for the wheat streak mosaic virus.” A burndown herbicide was applied in the fall and preplant in the spring to control volunteer wheat.
The initial impetus for surface applications of trifluralin and ethalfluralin granules came from the north — specifically, the prairie provinces of Canada, where no-till producers of oilseed and pulse crops have been seeking additional herbicide options for their direct-seeding production programs. (Continued)
In a series of experiments involving DowElanco, Ag Canada and various producers during 1993 and 1994, surface applications of ethalfluralin (marketed as “Edge” in Canada) granules were compared to shallow incorporation with rotary harrows. Results indicated that fall-applied ethalfluralin granules were superior to a spring-applied treatment in both the degree and consistency of weed control.
The fall-applied granules, at 1.25 pounds active ingredient per acre (with either no incorporation or incorporation by a rotary harrow), provided 85 percent control of those grass and broadleaf weeds presently listed on the “Edge” label. According to DowElanco, a shallow incorporation with rotary harrows had little effect on weed control of the fall-applied granules.
In the spring-applied tests, the granules were applied at 1.0 pound ai/A and incorporated with rotary harrows. Control of several weeds on the Edge label averaged 80 percent or higher. “In spring, weed control on land that had been in direct seeding for three years or greater was more consistent than on land that was less than three years in direct seeding,” DowElanco reports.
Mark Peterson, a Fargo, N.D.-based technical service and development specialist for DowElanco, nods in agreement with that last statement. “This system of surface application tends to work best in fields that have been in no-till for at least three years,” Peterson confirms, “because after you’ve been in no-till for awhile, that weed seed bank gets concentrated close to the surface. Because these herbicides are pretty insoluble, even with snowfall or other precipitation, you’re not going to move them very deep into the soil — probably not much more than an inch or so.
“If you went to no-till just recently, you’ll still have a significant amount of weed seed that is two to three inches deep,” he continues. “It will germinate from those depths and not be controlled from a surface application. You’re just not getting the chemical down to where the weed seeds are germinating.”
Like other DowElanco personnel, Peterson cannot and does not actually recommend that sunflower growers use a nonincorporated surface application of either Treflan or Sonalan granules. Based on research and his experience, however, he does offer some thoughts for no-till growers who may be considering this method.
“They need to approach it with a different mindset [compared to conventional tillage applications],” Peterson says. “A number of times, it’s going to work; but now and then, they’re probably going to have to rescue a field with some postemergence grass control.
“It’s not like other herbicide programs where you can count on that base treatment working most of the time,” he continues. “In this case, there might be a fourth of the time where it doesn’t work. Averaged over a number of years, though, they’d probably save themselves some money versus what they’d spend going strictly postemergence.”
Compared to mechanically incorporated granular applications, weed control via the surface route obviously will be much more dependent upon weather. That’s why a fall surface application commonly makes more sense in Canada or North Dakota while spring-applied granules would find a better fit in the High Plains. A couple key factors come into play:
First, the granules must be applied far enough ahead of planting to allow for adequate precipitation for the necessary chemical activation. With the Northern Plains’ long winters (1996 being a prime example) and ensuing hectic spring fieldwork schedules, this window may not be long enough if spring application is being considered. That’s typically not a problem for High Plains producers, however.
Secondly, snow cover often comes and goes on High Plains fields; late fall/winter temperatures can become quite warm; and sunlight striking granules atop the ground can stimulate degradation of the chemical. In the Northern Plains, by contrast, the granules normally remain covered by snow the entire winter. Even if fields are bare, the sunlight of winter is not as direct or intense as it is hundreds of miles to the south.
So what’s the current bottom line on surface applications of granular herbicides for weed control in sunflower?
• It does work, though probably not as consistently as a mechanically incorporated treatment.
• You’ll need adequate moisture for activation via melting snows or some significant spring rains.
• Weed control probably will be better in fields which have been in no-till for several years.
• Along with the surface granules, you may also need a preplant burndown treatment — and, in some instances, perhaps a postemergence herbicide.
• You’ll likely want to use high-end labeled rates.
• A surface application of trifluralin or ethalfluralin granules is legal as long as you don’t exceed labeled rates. But if, for whatever reason, results are not satisfactory, you have no recourse against the manufacturer.
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