Herbicide cross‐resistance inRanunculus acrisL. subsp.acris

The responses of seed‐derived progenies of an MCPA‐resistant (R) and an MCPA‐susceptible (S) population of Ranunculus acris to a range of doses of MCPA, 2,4‐D, MCPB, chlorsulfuron, and thifensulfuron were compared under glasshouse conditions. In a second experiment, also under glasshouse conditions, the responses of R and S to the usual field doses of tribenuronmethyl, bentazone, glyphosate, clopyralid, and asulam were compared. R was cross‐resistant to both 2,4‐D and MCPB. There was temporary cross‐resistance to chlorsulfuron and thifensulfuron manifest in slower development of apical mortality in R plants but all R and S plants ultimately died at the usual field dose rates of these two herbicides. There was weak evidence of cross‐resistance to bentazone but no evidence of resistance to either tribenuron‐methyl or glyphosate since both resulted in 100% mortality of R and S at usual field dose rates. Clopyralid and asulam had no effect on either R or S. The results indicate that neither 2,4‐D nor...