Evaluation of four different crops’ sensitivity to sulfosulfuron and tribenuron methyl soil residues

ABSTRACT

On the basis of greenhouse bioassays, the sensitivities of root and shoot biomass of barley (Hordeum vulgare L.), corn (Zea mays L.), oilseed rape (Brassica napus L.) and sugar beet (Beta vulgaris L.) to soil-incorporated sulfosulfuron and tribenuron methyl were assessed. Shoot and root biomass production was measured 30 days after emergence. Plant responses, including roots and shoots dry weight per pot, were described by a three parameter log-logistic regression model as a function of sulfosulfuron or tribenuron methyl doses and the relative sensitivities were calculated at the various ED-levels with their associated 95% confidence intervals. The most precise ED-levels were that at ED₅₀ and sensitivity rank was oilseed rape, sugar beet, corn and barley, whatever the chosen response level and herbicide. We calculated relative sensitivities at ED₁₀, ED₅₀ and ED₉₀ for the species of barley, the most tolerant crop, as reference. Comparison of relative sensitivity of crops to both herbicides showed that the sensitivity of these crops was much larger for tribenuron methyl than for sulfosulfuron. Oilseed rape was the most sensitive species (ED₅₀?=?0.202 and 0.179?µg?kg^?1 soil for root dry weight (RDW) response to sulfosulfuron and tribenuron methyl, respectively) while barley was the most tolerant one (ED₅₀?=?1.008 and 3.68?µg?kg^?1soil for RDW response to sulfosulfuron and tribenuron methyl, respectively). Sugar beet and corn had intermediate sensitivity. Also, we demonstrated how important it is to show the confidence intervals of relative sensitivities. In several instances the relative sensitivities, even numerically large, were not significantly different from 1.00. We demonstrate that classifying biotypes as resistant to a herbicide requires the threshold of resistance/susceptible (R/S) of 4.00 only be accepted if confidence intervals do not cover 1.00.