Resistência múltipla ao glyphosate e ao chlorimuron-ethyl em biótipos de conyza sumatrensis

Abstract

It is well known that the main herbicide used for weed control in production systems involving tillage is glyphosate. Lack of control after application of herbicides in areas with horseweed has been observed in several regions of the state of Parana. Thus, this study aimed at evaluating by means of dose-response curves the occurrence of resistant biotypes of Conyza sumatrensis in the state of Paraná, with the application of increasing doses of glyphosate applied in four distinct stages of development. In addition, analysis was performed to identify biotype of Conyza sumatrensis with multiple resistance to glyphosate and chlorimuron-ethyl. The experiments were conducted in a greenhouse, in which assessments were made of percentage of control (visual analogue scale 0-100% where 0% indicates no symptoms and 100% indicates death of weeds) and accumulation of dry matter air. To evaluate the resistance of C. sumatrensis to glyphosate, eleven suspected resistant biotypes were tested, as well as a susceptible biotype. The doses used were: 0, 90, 180, 360, 720, 1440, 2880, and 5760 g ha-1. From the results obtained in the first trial, it was shown that there is difference in the control provided by glyphosate applied at different stages of development, beyond the confirmation of resistant biotypes. For applications accomplished in the first stage of development, biotypes resistant to glyphosate were Cascavel-1 and Tupãssi-6. For applications in the second stage of development, beyond the biotypes found in the first stage, we found six other cases of resistance. However, for applications made at third and fourth stages, all biotypes were considered resistant (F>1.0 and I80>720 g ha-1). To evaluate the multiple resistance of Conyza sumatrensis to the herbicides chlorimuron-ethyl and glyphosate, four populations (Cascavel-2, Toledo-4, Tupãssi-6, and Assis Chateaubriand-7) with suspected resistance were tested against a susceptible population. For the dose-response curve eight increasing rates of glyphosate (0, 90, 180, 360, 720, 1440, 2880, and 5760 g e.a. ha-1) and chlorimuron-ethyl (0, 2.5, 5, 10, 20, 40, 80, and 160 g ha-1) were applied. The results confirmed the resistance of two biotypes (Cascavel-6 and Tupãssi-2) to glyphosate and of four biotypes to chlorimuron-ethyl (Cascavel-2, Toledo-4 Tupãssi-6, and Assis Chateaubriand-7). Therefore, multiple resistance to both herbicides was confirmed for C. sumatrensis biotypes Cascavel-2 and Tupãssi.