Net economic benefit of Ranunculus acris control in dairy pasture – accounting for herbicide damage to clovers and evolved resistance

The phenoxy carboxylic acid, ALS-inhibitor and pyridine carboxylic acid herbicides vary in the magnitude and duration of Ranunculus acris control in dairy pastures and in collateral damage to clovers. For estimating the net economic benefit from a proposed herbicide treatment, we developed a model accounting for these sources of variation. Applied to a hypothetical dairy pasture with 12 tonnes dry matter/ha/year eaten and assuming present-day costs and prices (e.g. herbicides, nitrogen fertiliser, milksolids pay-out), the model illustrates the expected increase in net benefit with increasing pre-treatment R. acris cover. It also predicts lower breakeven covers (CBE) for the phenoxys (MCPA CBE = 3.72%; MCPB CBE = −0.88%; MCPB + bentazone CBE = 1.51%) and ALS-inhibitors (flumetsulam CBE = 1.88%; thifensulfuron methyl CBE = 1.50%) than for the pyridines (aminopyralid CBE = 7.24%; aminopyralid + triclopyr CBE = 5.72%), a result of their lower costs and lower and less-enduring clover damage compared to the pyridines. A greater uncertainty in the net benefit from the phenoxys and ALS-inhibitors results from a greater paddock-scale variation in their efficacy, a characteristic attributable to evolved resistance. The model is available as a weed control decision-support tool at https://giant-buttercup-ds-tool.azurewebsites.net/