Managing Glyphosate-Resistant Palmer Amaranth
by Mike Marshall
SITUATION: Glyphosate-resistant Palmer amaranth was first reported in cotton in 2004.
DISTRIBUTION: Nine counties are infested, most with a light to moderate infestation.
IMPACTS: The occurrence of glyphosate-resistant Palmer amaranth doubles the cost of effective weed control. The herbicides that are the basis for weed control of glyphosate-resistant Palmer amaranth rely on timely rainfall or irrigation for activation to be effective for weed control. In some fields in summer of 2007, growers could not harvest their crop due to their inability to control Palmer amaranth.
RESEARCH: Surveys are being conducted in 2008 to gather more information on the occurrence of Palmer amaranth resistance in South Carolina. Research is planned for summer 2008 to evaluate alternative herbicide chemistries in Roundup Ready and conventional soybeans, including glufosinate (Liberty®, Ignite), flumioxazin (Valor®), and fomesafen (Reflex®, Flexstar®), for control of glyphosate-resistant Palmer amaranth.