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Weed pressures abound

Jeff Caldwell 06/15/2011 @ 12:37pm Multimedia Editor for Agriculture.com and Successful Farming magazine.

If you're in an area where you've faced big rain after big rain this spring, you may be wondering how your herbicides are performing in the field. And for good reason: In a wet year like this year, those herbicides probably aren't performing at their full potential.

"I'm in central Nebraska, and I have never seen so many fields with so many weeds in them as this spring, mine included," says Agriculture.com Crop Talk member Nebrfarmr.

And, other farmers say this spring's weather has caused some unusual conditions, not just more weeds in general. Crop Talk member nwobcw says he's seeing altogether different weeds than he has ever seen before in his area and speculates a nearby tornado earlier this spring possibly brought the seed into the area. And, Crop Talk member hymark says the wet weather in his area of southwestern Ohio has more of several weed species in varying sizes.

"Weed heights and populations are all over the board; more thistles some places, more ragweeds some places, poison hemlock everywhere. All getting out into fields again," he says.

Hymark's observations are common around the Corn Belt this year, especially regarding the number of different weeds that could become problematic, according to a group of Purdue University Extension weed scientists led by Bill Johnson.

"In a year like we have been experiencing, where heavy rains have delayed planting and the preemergence herbicides have been under pressure, we will in all likelihood see a number of weeds emerge in both corn and soybean fields," Johnson says.

This year, Johnson and fellow Purdue weed scientists Glenn Nice and Tom Jordan say in a university report that there are 13 weeds -- the "Dirty Bakers' Dozen Weeds" -- that all face an easier-than-normal path to maturity this year because of wet conditions:

  • Morningglories
  • Waterhemp
  • Burcucumber
  • Fall panicum
  • Common ragweed
  • Giant ragweed
  • Yellow nutsedge
  • Shattercane
  • Crabgrass
  • Lambsquarters
  • Smartweeds
  • Nightshades
  • Barnyardgrass

So, what can you do? It depends on both the severity of each weed's infestation as well as the number of different weeds present. In some cases, a single glyphosate application can do the trick. If that's not stiff enough, Johnson recommends looking into more specific products labeled for different species.

"A single application, or even a second application of glyphosate or Ignite may not be enough to control some of these weeds. Depending on the weed population mix in an individual field, additional herbicide choices may be needed to control these herbicides," he says. "There is a large choice of postemergence herbicides labeled for these weeds, but care is needed to make the right choice, and timing for weed height and corn growth stage in critical to make these herbicides work."

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