Response of Conyza bonariensis, Conyza canadensis and Conyza sumatrensis to glufosinate

Conyza bonariensis, C. canadensis and C. sumatrensis are problematic weeds in citrus orchards and olive trees in southern Spain. The aim of this work was to determine the efficacy of glufosinate in these species, and also to establish a suitable growing stage for application in C. bonariensis. For this purpose, dose-response and spray retention assays were carried out in susceptible biotypes of C. bonariensis, C. canadensis and C. sumatrensis at the rosette stage (BBCH 14-15). Additionally, the ED50 and spray retention at two later growth stages were determined in C. bonariensis. Results at rosette stage (BBCH 14-15) showed an ED50 of 0.216 in the case of C. bonariensis; 0.058 for C. canadensis and 0.090 L ha-1 for C. sumatrensis. The spray retention values did not show any significant differences between the three species at rosette stage. In C. bonariensis, at the second stage of its growth (10-15 cm in height), the ED50 obtained was 0.517 and 1.297 L ha-1 for the third stage (with formed capitula). Also, the spray retention in the second and third stage was of 0.44 and 0.38 mL of glufosinate g-1 of dry weight, respectively. These species treated in an early developmental stage are more susceptible to glufosinate herbicide.