Three UK sterile brome (Anisantha sterilis syn. Bromus sterilis) populations have been found to be in the process of evolving glyphosate resistance after showing reduced sensitivity to the herbicide. The populations were incompletely controlled at UK recommended field rates of glyphosate for annual grass weed control (540 g/ha) and are significantly less sensitive to glyphosate than 29 random UK sterile brome populations and 3 sensitive populations (Figure 1). The full open-access article can be found here.
Figure 1: Mean percentage control fresh weight of 35 UK sterile brome populations treated at half the recommended field rate of glyphosate. Three populations, 09D118, OXON-R, and SEL-R were found to have reduced sensitivity to glyphosate, sitting outside the range of sensitivity of the remaining 32 populations.
Although the three populations show reduced sensitivity to glyphosate, dose-response resistance indices were low, ranging from 1.55-4.5, and ED50 values (the estimated dose at which 50% of the population will be controlled) ranged from 420-810 g/ha (Figure 2). Showing that the populations are not currently resistant to glyphosate, but are adapting to glyphosate selection.
Figure 2: Glyphosate dose-response ED50 values of 11 UK sterile brome populations, with 3 populations, SEL-R, OXON-R, and 09D118, showing reduced glyphosate sensitivity compared to the remaining populations.
The detection of these populations highlights the need for glyphosate stewardship to help prevent resistance evolution. Two of the populations (SEL-R and 09D118) were from fields with a long history of minimum tillage or direct drilling, a high risk strategy for glyphosate resistance evolution, showing the need to combine both cultural and chemical weed control to help prevent resistance. In 2015, the Weed Resistance Action Group (WRAG) released guidelines with four key messages to help minimise the risk of glyphosate resistance (Figure 3). The WRAG guidelines were slightly updated in 2018 and can be found here.
Figure 3: Four key steps in the WRAG guidelines to help minimise the risk of glyphosate resistance
The research was carried out during the PhD of ADAS weed researcher Laura Davies, with Rothamsted researchers Richard Hull, Stephen Moss, and Paul Neve.