Journal or Publishing Institution: California Agriculture
Author(s): Shrestha, A. and Hembree, K.
Article Type: Report
Record ID: 2364
Abstract: Glyphosate-resistant horseweed biotypes have been reported in 10 states in the US, mainly in annual row-crop systems. This study showed that glyphosate-resistant (R biotype) horseweed also exists in California. The level of resistance to glyphosate, however, was influenced by the stage of growth of horseweed at the time of glyphosate application. There was a probability of controlling some of the ‘R’ biotype horseweeds at the 5-8 leaf stage with a 2x or 4x rates of glyphosate. After the 18-21 leaf stage, the horseweed plants were able to survive glyphosate application rates up to 4 lb ai/ac. At later stages, even some plants of the ‘S’ biotype escaped the lower rates of glyphosate. Therefore, it is important to control horseweed at an early stage of growth. This is the first case of glyphosate-resistant horseweed biotype existing in a non-crop situation. An integrated weed management program will have to be developed to manage glyphosate- resistant horseweed biotype in the South Central Valley.
Keywords: glyphosate-resistant horseweed, South Central Valley
Citation: Shrestha, A. and Hembree, K., Glyphosate-resistant horseweed (Conyza canadensis L. Cronq.) biotype found in the South Central Valley. California Agriculture, 61, pp.267-270.
