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Rotation Bolsters S.D. Broadleaf Management

Monday, February 1, 2010
filed under: Weeds

Raymond Roghair of Okaton, S.D., uses rotation and an aggressive pre-plant burndown regime to control weeds in his sunflower fields.

Roghair farms in Jones County, about 50 miles southwest of Pierre, on soils that he describes as “very, very heavy clay over shale.” Working with an average rainfall of 16.5 inches, he uses as many as nine crops — all planted under no-till — in his rotation. He selects his fields carefully for sunflower with the understanding that he does not have a rescue treatment in the event of a broadleaf weed outbreak.

Roghair plants sunflower after winter wheat, starting his weed control program in August of the wheat year. He uses 16 oz of glyphosate with 0.5 lb of LV6 in August after his winter wheat has been harvested and weeds have had a chance to germinate.

A rain after the wheat harvest will get the shallow weed seeds germinating and the August timing provides a good weed kill as well as eliminating soil moisture loss from growing weeds.

His next application of glyphosate is an 8-oz treatment sometime in October. This kills volunteer wheat and downy brome that have germinated from fall rains. “I can go into freeze-up knowing that I have a fairly clean seedbed for my next crop of sunflower,” Roghair points out. “It all depends on when and how much moisture we get to germinate the weed seeds after winter wheat harvest. I can go to another crop with more herbicide choices if August and September have been inordinately dry.”

This South Dakota producer’s preplant weed control program consists of 20 oz of glyphosate with 1/3 lb of LV 6 in early May. He then follows up with another quart of glyphosate at planting or before emergence. Poast, Assure II or Select can be used late to eliminate any grasses that emerge. With careful field choice and an aggressive burndown program, broadleaf weeds have not been a problem — “no seed, no weed.”

Roghair has tried Spartan, but he says it is too rain-dependent to be adequately incorporated in his dry locale. “In our limited rainfall of southwestern South Dakota, we can go for quite a while without a rain. I just can’t depend on a well-timed rainfall event [occurring] to incorporate a herbicide,” he states.

Roghair did try a Clearfield® hybrid in the early introduction stage of the technology. “I didn’t like that particular hybrid at that time, so I have not gone back,” he explains. However, he likes to plant as early as possible, and the new and improved Clearfield or ExpressSun® hybrids would be a good option for earlier planting, Roghair believes. A limiting factor with the ALS herbicides is resistant kochia. It is his most prolific and troublesome weed, and he does have resistant kochia on his farm. But those herbicide-tolerant hybrids are an option on the table.

Roghair follows sunflower with spring wheat or oats. “I plant those crops very early in the spring, and I have sufficient herbicide choices to kill off whatever broadleaf weeds may be coming up along with volunteer sunflower,” he observes. He doesn’t have any problem getting his wheat or oats to emerge despite the short time-frame between his sunflower harvest and early spring planting. “The rule in no-till is to follow a deep-rooted crop like sunflower with a shallow-rooted crop such as wheat or oats. It has certainly worked on my farm,” Roghair attests.

Another good reason for including sunflower in his rotation is its tolerance to salinity. “We continue to see saline spots develop with our heavy clay soils, and sunflower is the best crop we have to handle the salt. Once the plant is established in a saline area, it will thrive and take out moisture,” Roghair says. Sunflower is well recognized as being a salt-tolerant crop. He believes there may be salt-tolerance differences among hybrids as well.

Roghair’s five-year average sunflower yield is right around 1,700 lbs/ac. However, 2009 was an exceptional year with timely rainfall. “We averaged well over a ton this year and pushed the 2,500-lb mark in several fields,” he reports. —Larry Kleingartner

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