An approach to investigate the costs of herbicide‐resistant Alopecurus myosuroides

Summary Herbicide resistance in Alopecurus myosuroides causes severe problems in Western European cropping systems. Costs of herbicide resistance were investigated in this study by analysing variable production costs and sales revenues. Three farms were selected for this study, with winter wheat as the dominating crop in all farms. Resistance in A. myosuroides populations was verified at all locations. Four farming approaches were simulated over a period of 20 years: (i) continuing the actual cropping system without increase of resistance, (ii) continuing the actual cropping system with increase of resistance, (iii) changing cropping practice to overcome resistance and (iv) changing cropping practice to prevent resistance. Contribution margins representing the proportion of sales revenue that is not consumed by variable costs were calculated for all approaches. Comparative static simulations showed that average contribution margins in a cropping system with more than 60% winter cereals and reduced tillage practice dropped from 807 € ha −1 a −1 without herbicide resistance to 307 € ha −1 a −1 with herbicide resistance. Alopecurus myosuroides population densities increased to more than 1000 plants m −2 . Diverse crop rotations, including spring crops, clover–grass leys and intensive tillage, suppressed A. myosuroides populations, and average contribution margin was 630 € ha −1 a −1 . Preventive methods with rotations of winter cereals and spring crops with less clover–grass leys resulted in an average contribution margin of 691 € ha −1 a −1 . In conclusion, rotations of winter cereals and spring crops combined with inversion tillage and herbicides provide stable yields and can prevent weed population increase.