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Extension > Minnesota Crop News > First Steps to Taking Control of Herbicide-Resistant Weeds - Attend the 2011 CPM Short Course

First Steps to Taking Control of Herbicide-Resistant Weeds - Attend the 2011 CPM Short Course

Now is the time to develop a plan and take control of herbicide-resistant weeds before they take control of you. Due to the long-term exposure to glyphosate in the corn and soybean cropping system, we are now in a situation where the probability of finding a glyphosate-resistant giant or common ragweed or waterhemp is high.

Key reasons why glyphosate has been used so extensively is its ease of use and low-cost effective contributions to end-of-season profitability.  This has been a welcome tool in a business where factors such as weather and the markets influence on profitability are out of the producer's control.  Such challenges are frustrating, but they are a good reminder to the farmer to take control of the crop management decisions that can be controlled.

Currently, glyphosate-resistant weeds are a serious problem in the southern United States, resulting in significant increases in herbicide and labor costs, and increased field applications. The situation isn't as dire in the Upper Midwest now, but the trend with herbicide-resistant weed development in a field is a slow start that can grow exponentially by the next growing season.

As a first step to taking control I would like to invite you to attend the 2011 CPM Short Course and MCPR Trade Show at the Minneapolis Convention Center December 13-15, 2011.  On Thursday, December 15th Dr. Larry Steckel, Extension/Research Weed Specialist from the University of Tennessee will present: Glyphosate-Resistant Weeds -Lessons Learned in Tennessee.  Dr. Steckel will make it quite clear that a proactive approach to herbicide resistance management is more profitable than a reactive approach.

To proactively address glyphosate-resistant weeds, you must reduce your total reliance on glyphosate and diversify your weed-management practices, with more emphasis on spring and early-summer weed control and a more focused use of glyphosate in the crop where its weed control is of greatest value to you.

I recommend the following strategies based on experience and extensive research conducted by University of Minnesota Extension and other land-grant institutions:

In all fields:

  • Select herbicide sequential and tank-mix partners for glyphosate that will effectively control the weeds that have become difficult for glyphosate to control.
  • Start with a pre-emergence residual herbicide to control early-emerging weeds and reduce the potential for crop yield loss due to weed competition from a delayed postemergence glyphosate application.
  • Glyphosate and postemergence tank-mix partners should be applied to 3- to 4-inch weeds for maximum effectiveness.

In fields currently infested with glyphosate-resistant weeds

  • Liberty Link corn and soybeans offer another postemergence herbicide strategy--the use of Ignite herbicide. Application to weeds 3 to 4 inches tall is critical, and best results are achieved when following a pre-emergence herbicide.
  • Limit glyphosate use in crops where effective herbicide alternatives to glyphosate exist.  Target glyphosate use in crops where its weed control is of greatest value to you.
  • Use inter-row cultivation.
  • Rotate to early-season competitive crops, such as small grains.

Take control of the situation now, so your weed seed bank doesn't remind you of your mistakes for many cropping seasons in the future.

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