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Hold Your Horses: Marestail Control Considerations

Pam Smith
By  Pam Smith , Crops Technology Editor
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Attempts to burndown this marestail on prevented planted acres didn't work very well in Missouri fields last summer. Those fields need tended before the 2016 planting season. (DTN photo by Pamela Smith)

DECATUR, Ill. (DTN) -- It seems more than a little ironic that the roots of the Pony Express started in St. Joseph, Missouri. Horseweed -- also known as marestail -- definitely sprinted across northern Missouri this summer.

I drive Missouri Highway 36 often. The road is also called "The Way of American Genius" because the celebrity likes of Walt Disney, J.C. Penney, General John J. Pershing and Mark Twain have ties to the small towns that lie between Hannibal and St. Joseph.

During the 2015 season, that area was also a hotbed for prevented and late planting. It didn't take a genius to see that horseweed was running loose on many of those fallow fields.

Stops in some of those fields found growers had tried to rein in the problem, but the weeds bested the treatments. Herbicide-resistant marestail has become a chronic problem in many states.

Four trips across Highway 36 during November were somewhat reassuring as I found several of those fields I'd noticed earlier rocking out with cover crops.

Still, Kevin Bradley, University of Missouri weed scientist, said he expected fields that didn't get planted last season to be trouble next spring since weeds made healthy deposits to the seed bank.

Marestail is at least one weed you can still corral this year since some portion of the marestail that went to seed will germinate in the fall.

"Dry weather kept a lot of it from germinating early this fall, but recent rains and some warm weather have stimulated some emergence," Bradley said. It's not necessary to wait until the marestail rosettes to make a fall herbicide application if you use a product containing a residual.

However, Bradley noted that many growers are cutting costs and one way to do that and still make a fall application is to use a non-residual burndown application such as glyphosate and 2,4-D. In that case, you'll need the weed actively growing and the herbicide in contact with the weed.

How late is too late? "It usually depends on weather and our ability to spray with temperatures above freezing," Bradley said. "Usually mid-to-late November is when we have to stop, but I've seen years with us spraying into December.

"As long as we have days with temps regularly in the 40s and 50s, I think we are fine to still make a fall application. You just want to make sure you have time to get the herbicide on the plant, in the plant and allow it to translocate throughout the plant."

Hold your horses. Fall applications are likely just the first step in a series of steps needed to get this bad boy under control. Just keep in mind that many marestail populations are now resistant to glyphosate and in some cases, ALS-inhibiting herbicides (Group 2).

For more information on marestail control go to:

http://ipm.missouri.edu/…

http://agcrops.osu.edu/…

http://cropwatch.unl.edu/…

Pamela Smith can be reached at Pamela.Smith@dtn.com

(CZ)

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