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New Weapon in Toolbox for Sunflower Desiccation

Wednesday, September 1, 2010
filed under: Optimizing Plant Development/Yields

Sunflower growers have access to a new desiccation tool in 2010. That tool is Sharpen® (saflufenacil), part of the Kixor herbicide group from BASF. Sharpen actually received a full Section 3 label from EPA in late 2009 — too late to be used in the field.

The product has been researched as a desiccant on sunflower starting in 2007, in four locations: Minot and Fargo N.D., Brookings, S.D., and Hays, Kan. This desiccation research, funded by the National Sunflower Association, compared Sharpen with already-labeled products such as Paraquat Inteon® and Roundup OriginalMax® (which is labeled for late-season weed control).

Although the 2009 season was a “bust” for this research (as were certain years in other locations), data point out that Sharpen will be a good option when fall weather conditions are conducive.

The data indicate that harvest can occur as much as 10 days earlier in North Dakota with the use of a desiccant. The results were not as significant in South Dakota or Kansas, where the numbers indicate no difference to a seven-day earlier harvest.

The advantage with Sharpen is that it is faster acting then Roundup Original. Gramoxone Inteon (Paraquat) is fast acting and kills the leaves quickly, but does not translocate. Sharpen is both a contact and systemic herbicide and does a better job of drying down the stem compared to Gramoxone, according to NDSU’s Kirk Howatt.

Another advantage over Graxomone is that Sharpen is not a “cell disrupter.” So the plant is not as likely to rehydrate if rainfall is received after an application of Sharpen. The combination of Sharpen and Roundup Original has advantages in better weed kill for late-season weed control.

When to pull the trigger on spraying a desiccant is a bit tricky. Spraying too late when seed moisture is under 30% does not provide much advantage in earlier harvest compared to the control of “no desiccant.” Labels specify desiccating at 36% seed moisture or less for Sharpen and 35% or less for the other labeled products.

Determining the exact seed moisture level is a guessing game at best. Oven drying seed samples and comparing the weights before and after oven drying is the most exact procedure. For field observation, Howatt likes to follow the drydown of the bracts. When the tip of the bract is brown, the seed moisture is between 50-40%. When the neck of the bract has turned brown, the seed is about 40%. When the shoulder of the bract is brown or dried, the seed moisture will be 30-35%.

Kansas State University weed scientist Phil Stahlman says seed moistures vary within the field and the head, so it will be impossible to peg the moisture level at an exact number. Seed moisture is going to be lower in the first seed rows of the head compared to the last-filling center. The key of this long-term research is that there has been no damage to oil content, seed size, test weight or yield when plants were desiccated at 40% seed moisture.

Additional research funded by the NSA and conducted by Dr. Burton Johnson of NDSU and Dr. Russ Gesch of USDA-ARS at Morris Minn., revealed that there are differences between hybrids when comparing seed moisture and physiologic maturity. The researchers looked at Mycogen’s 8N272 and Croplan’s 378 for physiological maturity, including yield, oil content and fatty acid composition. For yield, 8N272 and 378 reached maturity between 35-45% seed moisture. Oil content and fatty acid composition reached maturity between five to 10 moisture points higher.

This was from research conducted in 2008 and 2009 at Morris and Prosper N.D. These results, combined with the multi-state research team data, clearly indicate that erring on the high side of 35% seed moisture is not going to impact yield or quality.

There is no suggestion here of going off label. It is simply a summarization that determining physiological maturity and seed moisture within the field, within an individual head and between hybrids is going to vary by as much as 10 percentage points.

The importance of an early desiccant spray in the northern region is to take advantage of warmer temperatures in September. Herbicides work best with warm temperatures, allowing the plant to translocate the herbicide. “In northern North Dakota and Minnesota, it doesn’t usually make a lot of sense to desiccate in October since our killing frost is usually at that time,” Howatt says. But if the crop is mature in early September, there can be significant advantages in accelerating the harvest with a desiccant. “It still all depends on the weather after the application,” Howatt observes.

There are several reasons why desiccation should be considered. Stalk integrity is one. John Swanson of Croplan Genetics, a longtime sunflower agronomist, advises farmers and crop scouts to split a few stalks after petal drop to determine what kind of insect activity is taking place in that stalk. “If there is a lot of tunneling, it might make sense to desiccate and get that crop off as soon as possible to avoid stalk breakage later on,” says Swanson. The obvious blackbird issue in the north is an additional reason for pushing for early harvest.

Desiccation is a good tool for High Plains growers who want to get winter wheat planted on the sunflower stubble, says KSU’s Stahlman. “Otherwise, the heat units in the High Plains region are sufficient for natural drydown.”

Desiccation is another management tool that will not be an option each year. A good example was 2009, when the crop finally matured in late September due to the cool growing season. A killing freeze followed shortly thereafter throughout the entire production region as far south as Kansas. Researchers were not able to spray the desiccant because Mother Nature took care of it. — Larry Kleingartner

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