Weed Control in Soybeans and Resistant Weed Management Typical Soybean Field 10 Years Ago Marestail Escapes from Glyphosate Glyphosate Resistant Waterhemp in Eastern Kansas Herbicide Resistance WSSA Definition Resistance is the inherited ability of a plant to  survive and reproduce following exposure to a dose of herbicide normally lethal to the wild type. Tolerance is the inherent ability of a species to  survive and reproduce after herbicide treatment. This implies that there was no selection or genetic manipulation to make the plant tolerant; it is naturally tolerant. Herbicide Resistance Landmarks in Kansas 1976: Kochia resistance to atrazine.  1993: Waterhemp and Palmer amaranth resistance  to Pursuit and Pinnacle. 1995: Waterhemp and Palmer amaranth resistance  to atrazine and metribuzin. 2001: Waterhemp resistance to Cobra.  2005: Marestail resistance to glyphosate.  2006: Waterhemp resistance to glyphosate.  2009: Palmer amaranth resistance to Huskie.  Herbicide Resistance in Kansas Photosystem II: Kochia and pigweeds  ALS inhibitors: 11 species  PPO: Waterhemp  Glyphosate: Six species  HPPD: Palmer amaranth  PGR: Kochia?  Glyphosate Resistance in Kansas Marestail (2005): Common throughout KS.  Giant Ragweed (2006): Scattered through NE KS.  Waterhemp (2006): Common in eastern third of KS.  Common Ragweed (2007): Isolated in Eastern KS.  Kochia (2007): Common in western third of KS.  Palmer amaranth (2011): Scattered throughout and  increasing. Pigweed Escapes in Soybean Fields 9 Waterhemp populations – Eastern Kansas, 2011 Population: 4 3 2 0 0.75 (1X) 1.5 (2X) 3 (4X) Glyphosate rate, lb ae/a 10