Differential reaction of Alopecurus myosuroides biotypes to ACCase inhibitors.

The number of herbicide-resistant blackgrass populations (Alopecurus myosuroides Huds.) in winter cereal crops is increasing in Europe, leading to serious restrictions in cereal production. Moreover, resistant biotypes are often characterized by better fitness than sensitive ones. This study aimed to evaluate the reaction of potentially ACCase resistant biotypes of A. myosuroides to different doses of fenoxaprop-P-ethyl and pinoksaden. Seeds of seven populations of blackgrass collected in 2017 from winter wheat fields in north-eastern Poland were sown to pots filled with potting mixture. After germination, the number of plants was reduced to 5 per pot (3 pots for one herbicide dose). Both herbicides were applied at the 2-3 leaves stage at six doses from 0 to 8x label dose (LD). The 1 LD was equal to 1.2 L·ha^-1 for fenoxaprop-P-ethyl and 0.9 L·ha^-1 for pinoxaden, using a laboratory pot sprayer fitted with a boom with one nozzle calibrated to deliver 200 L·ha^-1 at a spraying pressure of 200 kPa. Three weeks after treatment, the fresh weight of shoots was recorded. Tested populations of blackgrass showed different reactions to applied herbicides. In fenoxaprop-P-ethyl treatment, the reduction of the biomass of treated plants was observed only for population number 1 compared to the non-treated control. Biomass of the remaining treated populations (2-7) was increased, especially for doses 0,5 LD – 4 LD. Pinkosaden treatment resulted in biomass accumulation decrease in 3 populations. In four biotypes (2-5), increased biomass accumulation was observed after treatment compared to the non-treated control. The results indicate that examined biotypes can induce mechanisms reducing the negative impact of applied herbicides; for some of them, the stimulatory effect was noted.