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Outwitting Weed Resistance

Soybean farmers have to stay one step ahead to control weeds. But, with broadleaf weeds becoming resistant to certain herbicides, it can be taxing just keeping up with what works, what doesn’t, and what new technology is available. Dr. Bob Scott, weed scientist with the University of Arkansas Cooperative Extension Service, discusses the development of new herbicide technologies to control weeds in soybeans in Arkansas. He urges the state’s soybean farmers to consider a new approach to weed control if the current method isn’t working.

Before doing any type of weed control, however, Dr. Scott recommends farmers consider a few questions first, including:

  • If your goal is to conserve moisture at planting time, and heavy vegetation is present, moisture reserves may already be depleted, and establishing soybean stands may not be feasible without rainfall.
  • In a dry year, failure to obtain good control of existing vegetation will result in failure to obtain a stand of soybeans because the weeds will deplete the soil moisture before the seedling soybeans can become established.
  • Spray volume for herbicides should be in the 10-to-20 gallon per acre range for best results.
  • Thorough and uniform coverage is necessary for good “burndown” results. Coverage is more dependent on droplet size and number of droplets (orifice size-pressure relationship) than on total volume.
  • Timely postemergence herbicide applications and, in some cases, cultivation will be necessary for full-season weed control.

Dr. Scott also notes that, compared to some burndown and residual mixtures, a burndown herbicide such as glyphosate, paraquat, paraquat + Sencor or Canopy followed by a total postemergence program has been cheaper and more consistent in no-till, stubble-planted soybeans. These new herbicides can help with both cost and consistency. If you try the new technologies Dr. Scott discusses, let us know your experience with them. To learn more, follow Dr. Scott on Twitter.

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