Stimulation of Early Post-Emergence Growth of Alopecurus myosuroides and Apera spica-venti Following Spray Application of ACCase Inhibitors

Resistance of blackgrass ( Alopecurus myosuroides Huds.) and silky bentgrass ( Apera spica-venti (L.) P. Beauv.) to ACCase inhibitors is a serious issue in winter cereals throughout Europe, especially as hormesis induced by herbicides has been observed in some populations. According to the literature, growth-stimulating herbicide rates are on the rise. The aim of this study was to assess the responses of A. myosuroides and A. spica-venti , which are potentially resistant to ACCase inhibitors, to fenoxaprop-P-ethyl and pinoxaden applied at rates up to 8 times greater than their registered rates. The reaction of A. myosuroides to fenoxaprop-P-ethyl and pinoxaden resulted in an increase in biomass gain in six and four populations, respectively. In one population of A. myosuroides , this increase was statistically significant (46.4% and 55.3%). All three potentially resistant A. spica-venti populations tested were at least partially stimulated by fenoxaprop-P-ethyl, while pinoxaden only stimulated the APSII population (significant increase of 43.8%). Predictions of the possible impact of herbicides on the reproductive potential of the tested populations allow genotypes to be identified whose reproduction may be stimulated by the herbicides. The results of this study indicate that the tested populations can induce mechanisms that reduce the negative impact of the applied herbicides, with some populations demonstrating the effect of stimulating the accumulation of biomass in the treated plants.