Consultant's Perspective on the Evolution and Management of Glyphosate-Resistant Kochia (Kochia scoparia) in Western Kansas

Glyphosate is the leading herbicide used in glyphosate-resistant (GR) crops and no-till production systems. Evolved resistance to glyphosate in kochia was first reported in Kansas in 2007. Shortly thereafter, GR kochia became prevalent in western Kansas. An online survey of crop consultants was conducted in fall 2012 to gain their perspectives on evolving glyphosate resistance in kochia in western Kansas, to gather information on how grower weed management practices have changed from before to after occurrence of GR kochia, and to assess the effectiveness of management practices used during 2011 to 2012. Results of the survey indicated increasing infestation of kochia from prior to 2007 (present in 47% of fields) through 2012 (present in 70% of fields). It was estimated that greater than one-third of the cropland in western Kansas was thought to be infested with GR kochia by 2012. Growers increased glyphosate use rates from an average of 0.8 to 1.22 kg ae ha−1 and application frequencies from 2.0 to 2.9 from the period before 2007 to 2012. The spread of GR kochia has resulted in changing weed management practices. During the survey period, growers reduced the exclusive use of glyphosate from 49 to 15% for GR crop fields and diversified weed management practices. Though other herbicides in addition to or in place of glyphosate were often applied prior to kochia emergence and were effective in more than half the fields, at least one-fourth of respondents reported inconsistent results with alternative kochia control practices other than tillage. These results are educational and helpful in developing both proactive and reactive tactics to manage GR kochia. Nomenclature: Glyphosate; kochia, Kochia scoparia (L.) Schrad. Glyphosate es el herbicida líder para uso en cultivos resistentes a glyphosate (GR) y en sistemas de producción con labranza cero. Kochia scoparia que evolucionó y adquirió resistencia a glyphosate se reportó por primera vez en Kansas en 2007. Poco después, K. scoparia GR se hizo prevalente en el oeste de Kansas. En el otoño de 2012, se realizó una encuesta en línea a asesores agrícolas para: recoger sus perspectivas sobre la evolución de resistencia a glyphosate en K. scoparia en el oeste de Kansas, recopilar información sobre cómo los prácticas de manejo de malezas de los productores han cambiado desde antes hasta después de la aparición de K. scoparia GR, y para evaluar la efectividad de las prácticas de manejo usadas durante 2011 y 2012. Los