Occurrence of Multiple Glyphosate-Resistant Weeds in Brazilian Citrus Orchards

Glyphosate is the most widely used herbicide for weed control in citrus orchards Brazil; therefore, it likely that several species have gained resistance to this and more than one resistant can be found same orchard. The objective was identify weeds glyphosate from different regions of São Paulo State (SP) determine how many are present within Seeds Amaranthus deflexus, A. hybridus, Bidens pilosa, Chloris elata, Conyza bonariensis, Digitaria insularis, Solanum Americanum, Tridax procumbens, which, as reported by growers, suspected glyphosate, were collected plants survived last application (>720 g acid equivalent [ae] ha–1) sweet orange Tahiti lime orchards. Based on dose–response shikimic accumulation assays, all populations B. T. procumbens sensitive glyphosate. However, pilosa Olimpia region (R-NS, R-PT R-OdA) showed signs based plant mortality rates 50% a population (LD50 = 355–460 ae ha−1). All C. D. insularis presenting ratios 1.9 27.6 low shikimate rates. americanum also resistance, with ranging 4.3 25.4. Most sampled presented occurrence glyphosate: Nossa Senhora—one species; Olhos D’agua Passatempo—two Araras—four Cordeiropolis Mogi-Mirim—up five species. results paper provide evidence multiple exhibited This underscores difficulties managing glyphosate-resistant which prevalent throughout country, such bonariensis insularis. presence these further complicates susceptible may develop resistance. In addition, S. identified first time.