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The Antidote for Marshelder

Saturday, January 15, 2005
filed under: Weeds

If marshelder was the poison in your sunflower last year, than Clearfield™ was the antidote.

Marshelder was a weed that seemed to take advantage of last year’s cool growing season. It usually emerges before sunflower is planted. Growers usually control it through cultivation and/or a glyphosate burndown at planting. However, cool conditions delayed germination of marshelder (and other weeds), which then competed with emerging sunflower.

The only real post-emerge option for controlling weeds like marshelder and cocklebur in sunflower is by growing Clearfield sunflower, and applying Beyond (imazamox) herbicide, which provides contact and residual activity on a number of grasses and broad leaf weeds.

“The soybean price and weather problems last spring resulted in fewer Clearfield acres planted then we were hoping. But weed control performance and results of the sunflower acres that were planted to Clearfield were excellent,” says Vince Ulstad, senior field biologist for BASF, which makes Beyond for Clearfield sunflower hybrids.

Ulstad says that both the presence of marshelder and the effectiveness of Clearfield/Beyond in controlling the weed were clearly evident in 2004.

“More and more, that’s a weed I’m seeing in sunflower, particularly this past year,” he says. “You could drive by fields and pick out the fields with marshelder, and Clearfield sunflower that had been sprayed. You can really see the difference. Marshelder is one weed that is very sensitive to Beyond.”

The earlier Beyond is applied within the recommended spraying window the better. Growers have the legal flexibility to spray up to the 8-leaf stage in cases when application is delayed, but weed control performance is best when Beyond is applied to Clearfield sunflower at the two to four leaf stage.

Control is better because weeds are smaller, and since the plant canopy isn’t as thick when both sunflower and weeds are smaller, the chemical has a better chance of working down to the soil, where Beyond offers residual activity. This residual activity is not as long as some other “Imi” herbicides such as Pursuit, but long enough for the label to require a rotation interval before planting some Imi-sensitive crops such as barley, potatoes, sugar beets, and canola (see label for specific application details; herbicide labels can be found online at

One tool in the toolbox

Clearfield hybrids have the best fit on fields where specific weeds, such as marshelder and cocklebur, are a problem. And oil and maturity of a number of Clearfield hybrids today doesn’t compare to that of many non-Clearfield hybrids, though that gap can be expected to improve with genetic improvements.

“You’ll hear comments from some growers who say that their Clearfield sunflower doesn’t measure up to the oil content of some conventional hybrids, but then you talk to another guy who will say that he’s producing more oil per acre because he’s getting better weed control and more yield per acre,” says Ulstad.

He says that as a new technology, Clearfield hybrids are still evolving, and more hybrids with improved genetics are on the way. “I’m excited about the project when I look at the hybrids that seed companies have coming out. You look at the plot trials, and you can see some really good materials coming along that’s going to give growers a lot more choices in the Clearfield lineup.”

Mycogen agronomist Bruce Due agrees. “Among the hybrids we evaluated this summer, one looks to give us a 43-44 average oil, so it’s coming along,” he says. “What I tell growers now is that if they grow Clearfield which falls short on oil, they may need to look at selling into the bird food market.”

Growers should view Clearfield sunflower hybrids as one tool in the toolbox, and use them on fields where they’re needed. “Pick your fields. There are many fields where other hybrids are a better choice. But if you’ve got marshelder or cocklebur problems, you may lose five, six, seven hundred pounds of yield if it isn’t controlled. Then, there’s no doubt that the genetic potential of current Clearfield hybrids will far exceed anything out there planted into a marshelder environment.” – Tracy Sayler

Key Points about Clearfield Sunflower

• Clearfield is not the same chemistry as Roundup-Ready (glyphosate). Beyond herbicide is a member of the imidazolinone chemical family. Its active ingredient is imazamox.

• While the Clearfield system is available for several different field crops, including corn, wheat, rice, and canola, the “Imi” chemical formulations are not interchangeable. Thus, for example, Lightning is labeled only for use on Clearfield corn hybrids, not Clearfield sunflower hybrids. As well, one would not apply Beyond on Clearfield corn hybrids.

• Clearfield sunflower is not cross-tolerant to the sulfonylurea (SU) family of herbicides.

• Beyond must be applied only to Clearfield hybrids. Application of Beyond in conventional, non-Clearfield sunflower will result in significant crop injury and plant death.

• Clearfield is not a complete weed control program for sunflower. It helps growers manage pigeongrass/foxtail, wild oats, wild mustard, marshelder, cocklebur, devil’s claw (apply before the weed grows more than 4” tall) and other tough grasses and broadleaf weeds that plague sunflower growers, but does not take the place of other herbicide treatments that may still be needed in sunflower, such as preplant treatments.

• Clearfield has some activity against kochia, but should not be expected to give complete control. Growers will need to use Clearfield in combination with other herbicide strategies such as Spartan (sulfentrazone) or another pre-emerge herbicide product, and consider a glyphosate burndown at planting as well.

• Clearfield sunflower should be grown in rotation with other crops, and use alternate mode-of-action herbicides and tillage, to help prevent the formation of herbicide-tolerant weeds.

• Pyrethroids (Warrior, Asana XL, Baythroid, Scout X-Tra) are safe to tank mix with Beyond. Other chemistries, such as organophosphates (Lorsban, parathion) and carbamates (Furadan) may result in plant injury in Clearfield sunflower. Refer to the Beyond label for more details.

• The need for good sprayer cleanout when switching from one chemical to another is already obvious, and is something to watch as well when adding Clearfield sunflower to your crop mix. Sunflower is highly sensitive to herbicides such as 2,4-D, picloram, dicamba, MCPA, Ally, and Amber. And non-Clearfield sunflower is highly sensitive to Beyond. Use caution as well to prevent drift when spraying Clearfield sunflower near non-Clearfield sunflower.

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