New Zealand Journal of Agricultural Research abstracts

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Herbicide cross-resistance in Ranunculus acris L. subsp. acris

G. W. BOURDÔT
G. A. HURRELL
D. J. SAVILLE

AgResearch
Canterbury Agriculture & Science Centre
P. O. Box 60
Lincoln, New Zealand

Abstract  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 tribenuron-methyl, 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 MCPB will be useful for killing MCPA-resistant R. acris, except at very high dose rates but that glyphosate and the sulfonylureas tribenuron-methyl, chlorsulfuron, and thifensulfuron should provide a high level of kill at usual dose rates. The cross-resistances imply that the MCPA-resistance mechanism in R. acris also confers resistance to MCPB and 2,4-D and a lower, temporary resistance to the sulfonylureas chlorsulfuron and thifensulfuron. The nature of the resistance mechanism is not revealed by this study.

Keywords  Ranunculus acris; giant buttercup; dairy pasture; weed control; herbicide cross-resistance

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