Abstract
Abstract Brassica rapa L. is an important weed in winter wheat, barley, and other winter crops, and its control has become more difficult due to the development of resistant biotypes. The aim of this study was to record the presence of a B. rapa biotype resistant to 2,4-D herbicides and to evaluate the effect of different formulations of 2,4-D and other auxin herbicides on this biotype. Three independent dose-response experiments were conducted to evaluate: (i) the sensitivity of the resistant and susceptible B. rapa biotypes to increasing doses of 2,4-D, (ii) the sensitivity of the resistant biotype to different formulations of 2,4-D (butyl ester, dimethylamine salt, acid, and choline salt), and (iii) the sensitivity of the resistant biotype to other auxinic herbicides (picloram, dicamba, fluroxypyr, clopyralid and MCPA). The B. rapa resistant biotype showed a resistance index of 4.7, which means that, to achieve 50% inhibition of survival, the dose required needs to be approximately five-fold higher that required for the susceptible biotype. The GR50 of the resistant biotype for the different 2,4-D formulations marketed in Argentina was variable. The 2,4-D acid microemulsion formulation was the product that showed the highest control efficiency and biomass reduction. The resistant biotype was not susceptible to clopyralid, dicamba, or picloram, with maximum phytotoxicity of 25%, even when treated with four times the recommended dose and without biomass reduction, showing cross-resistance.
Published Version
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