ECONOMICS OF IMPROVED SPATIAL-DISTRIBUTION OF HERBICIDE FOR WEED-CONTROL IN CROPS

There are various causes of unintended spatial variability of herbicide dose in a crop, but each causes a reduction in profitability. The specific problem of spatial variability of the herbicide diclofop-methyl in postemergence control of ryegrass (Lolium rigidum) is examined. A model of wheat yield response to herbicide application has been implemented in a microcomputer and used to analyse the economics of spatial variability. The economically optimal herbicide dose was found to be insensitive to spatial variability, but marked effects on profitability were observed. The costs of spatial variation of herbicide are estimated to be as high as 25% of net returns in some scenarios. For this case study, profit was found to be more sensitive to variance of herbicide dose within the path of the spray boom (due to nozzle design, wind, boom roll, etc.) than to variance due to overlap or underlap of the boom in successive circuits of the field.