Economics of pre-emptive management to avoid weed resistance to glyphosate in Australia

Previous economic analyses of the preemptive use of strategies to delay the onset of herbicide resistance have concluded that they are often not economically attractive for selective herbicides, largely because the only effective delaying strategy is abstinence from use. However, in the case on the important non-selective herbicide glyphosate, the frequency of resistance genes is low enough for their local extinction to be possible. This can be exploited through the joint use of multiple control practices to seek the elimination of any weeds that survive glyphosate application. A particular version of this strategy, known as “double knockdown”, involves a follow-up application of paraquat after glyphosate. Biological modelling of this option has been encouraging. An economic model of the double knockdown strategy is presented, and used to calculate the break-even period before resistance onset. If glyphosate resistance is expected to occur before that break-even period, a farmer would benefit from adoption of the resistance-avoiding strategy, even though it is more expensive in the short term. Surveys of farmers indicate that some, but not all, would currently benefit from such a strategy.