Control Palmer Amaranth at Planting

The areas affected with glyphosate-resistant Palmer amaranth in Mississippi are continuing to increase.  The initial confirmation of glyphosate-resistant Palmer amaranth was made in 2008.  The number of affected counties increased to 11 in 2009, 24 in 2010, and 30 in 2011.

These counties occur in all crop production areas of the state.  But, there are likely additional counties that also have the problem.  Visit http://msucares.com/crops/weeds/resistant/index.html for more information on herbicide-resistant (glyphosate and/or ALS) Palmer amaranth in Mississippi.

Because of the warm weather in March, many fields already have high populations of Palmer amaranth.  Therefore, in fields that will not be planted for two or more weeks, a residual herbicide for Palmer amaranth in a burndown application is important.  Options for preplant residual herbicide treatments might include Reflex at 1 pint per acre for cotton and atrazine at 1 quart per acre for grain sorghum.

Several herbicides containing multiple modes of action against Palmer amaranth are available for preplant application to soybeans.  All these treatments should include paraquat (Gramoxone SL, Parazone, Firestorm) at 0.5 pounds active ingredient per acre to control any Palmer amaranth that is emerged at application.

For more information on control programs for glyphosate-resistant Palmer amaranth, see http://msucares.com/crops/weeds/index.html.

Regrowth on Palmer amaranth following paraquat application

Scouting fields between the time of the preplant residual herbicide application and planting will be critical.  Scouting will provide information on how well the preplant residual treatment performed, but will also be crucial for determining if Palmer amaranth emerged at application was completely controlled.  Paraquat is a great herbicide, but most of us have learned the hard way that 100% control of Palmer amaranth is the exception rather than the rule.  Paraquat may not provide complete control when Palmer amaranth exceeds six inches.

Paraquat is also a critical component of an at-planting herbicide application.  As with the preplant treatment, scouting fields before crop emergence will be necessary to ensure that any Palmer amaranth emerged at planting was completely controlled.  If survivors are found, then an additional paraquat application may be required prior to crop emergence.

Yearly use rates for paraquat vary by crop because it may be used in-season for some crops under certain circumstances.  However, paraquat labeling allows three applications prior to crop emergence for cotton, grain sorghum, rice, and soybeans.  Use paraquat judiciously to get an in-season weed control program off to a good start.  An ounce of prevention is worth a pound of cure, and unfortunately, there are few cures for Palmer amaranth.