Evaluation of saflufenacil on glyphosateresistant and glyphosate-paraquat resistant hairy fleabane (Conyza bonariensis)

Hairy fleabane [Conyza bonariensis (L.) Cronq.] is a problematic weed in crop and non-crop areas of California. This problem has been further aggravated by the discovery of herbicide-resistant biotypes. Three experiments were conducted to determine the efficacy of saflufenacil (TreevixTM), a fairly new herbicide, on glyphosate-susceptible (GS), glyphosate-resistant (GR), and glyphosate-paraquat-resistant (GPR) hairy fleabane plants. The studies evaluated the efficacy of saflufenacil when applied alone or in combination with glyphosate at: a) three growth stages (5- to 8-leaf seedling, rosette, and bolting); b) three temperature regimes (15/10ºC, 25/20ºC, 35/30ºC at day/night); and c) three light regimes (100%, 50%, 30%, 0% of full sun). Results differed between experiments conducted in the spring and fall. Saflufenacil-alone was more effective in the fall than in spring. All the GS, GR and GPR plants were controlled by saflufenacil-alone at the 5-to 8-leaf seedling and rosette stage but level of control declined at the bolting stage. Better control was obtained at the 15/10ºC and 25/20ºC than at the 35/30ºC temperature regime. Light regime had no effect on the efficacy of saflufenacil. Efficacy of saflufenacil-alone was inconsistent in spring and varied between the biotypes. Therefore, saflufenacil-alone can provide excellent control of hairy fleabane plants prior to the bolting stage in the fall; but in spring, it will be more effective when applied with glyphosate.