The economics of herbicide use in cereal crops in New Zealand

A simple model of net return for herbicide usage in cereals, based on yield losses caused by weeds, was used to derive breakeven losses for herbicides used in New Zealand. For wheat crops with average yields (4.5 t/ha) at 1987 prices, breakeven losses varied from 2.1% to 9.2% for weeds other than wild oats (Avena fatua), and from 6.4% to 14.1 % for wild oats. For barley crops with average yields (4.5 t/ha), breakeven losses varied from 3.0% to 13.1% for weeds other than wild oats, and from 9.1% to 20.2% for wild oats. A comprehensive survey of yield losses attributable to weeds in cereal crops has not been undertaken in New Zealand. However, using data available from Canada, breakeven yield losses would usually be exceeded for most of the 28 herbicides used in New Zealand cereal crops. On this basis there is no economic justification for the current trend toward reduced herbicide use in cereals.