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Unlike in the pesticide and antibiotic resistance literature, potential social costs and externalities associated with herbicide resistance have not generally been considered by economists. The economics of managing herbicide resistance in weeds has focused on cost-effective responses by growers to the development of resistance at the individual farm and field level. Economic analyses of optimal herbicide use have focused on optimising farmer returns in the long run. Weeds have been considered less mobile, compared to insects and diseases, suggesting that externalities resulting from resistance spread will be minimal and any consequent social costs low. Glyphosate is the world's most widely used broad-spectrum non-selective herbicide. Declining glyphosate prices, the adoption of no-till and minimum-till systems and the adoption of glyphosate-tolerant crops, have combined to cause a rapid increase in the use of glyphosate, and resistance is now appearing. In this paper we argue that the increasing possibility of widespread glyphosate resistance, exacerbated in some situations by spread through resistance mobility, presents a case where social costs associated with glyphosate resistance need to be considered when assessing optimal use of this herbicide resource at the farm level. Possible social costs associated with the loss of glyphosate efficacy include potential failure of herbicide-resistant crop systems, reduced use of conservation tillage techniques, and potentially more reliance on herbicides with greater environmental and health risks.

Perceptions are known to play an important role in the innovation adoption decision. Once influential perceptions have been identified, there is the potential for information to influence adoption by changing these perceptions. In this paper, the influence of an extension workshop targeting grain growers’ perceptions known to be associated with the adoption of integrated weed management and herbicide resistance management has been measured using regression analysis. Consistent with a Bayesian learning framework, the greatest influence on grower perceptions and intended adoption behaviour was observed where information could be delivered with a high degree of certainty and validity.

The Multi-species RIM (Resistance and Integrated Management) model is used in this analysis to investigate the value of Roundup-Ready® canola in the simultaneous management of annual ryegrass (Lolium rigidum) and wild radish (Raphanus raphanistrum). It is likely that the transgenic canola variety resistant to the non-selective herbicides glyphosate will soon be introduced in Australian agriculture. The perceived advantage of growing these crops is the potential to control post-emergent weeds with excellent broad-spectrum herbicides, and without the yield penalty evident in triazine-resistant canola (grown widely in WA). This may also help prolong the life of selective herbicides, to which ryegrass and radish can be highly resistant. Therefore, the introduction of genetically modified glyphosate-resistant canola will, other factors being equal, not only increase the options for weed control, but increase the yield of the vast canola crops grown in WA. Conversely, increased usage of the herbicide to which the new crop is resistant can result in the evolution of resistance to that herbicide in weeds. These trade-offs are discussed here.

Extension programs in Australia are encouraging farmers to adopt integrated weed management (IWM) practices, in order to delay the development of herbicide resistance in weeds infesting cropping land. Logistic and Tobit regression models were developed and used to analyse, survey data from Western Australian grain growers. Factors shown to influence IWM adoption included perceptions of IWM practices and expectations about the future of the herbicide resource. The results were consistent with the prior that farmers regard IWM as an information-intensive package of techniques, and that extension may have the potential to increase the rate of adoption.

A multi-species version of the bio-economic RIM (Resistance and Integrated Management) model has been developed to deal with the complexities involved in the long-term integrated management of annual ryegrass (Lolium rigidum Gaud.) and wild radish (Raphanus raphanistrum L.), which dominate and co-exist in southern Australia. In this paper, we present a review of the existing options on how to model multi-species competition in order to select the best approach for incorporation in the RIM framework. Furthermore, we show how we have extended the original single-species ryegrass RIM model to include other aspects of the wild radish biology as well as a set of extra weed management practices used to control this weed species. We also demonstrate how the Multi-species RIM model can be used to evaluate weed management scenarios of co-existing herbicide resistant species. This is done through investigating the implications of using Roundup Ready® canola in the system.

Herbicide resistance has become a major problem in Australian dryland agriculture. This situation has resulted from the repeated use of herbicides in place of the traditional weed control provided by cultivation and grazing. Farmers have addressed the problem of herbicide resistance by adopting a system of integrated weed management that allows weed control with a range of different techniques and herbicides. One of the non-chemical methods being considered by farmers is “green manuring”, which involves ploughing a healthy growing crop or pasture into the soil in order to prevent weed seed production and provide other benefits. In this study, the trade-offs between the effective weed control and biological benefits provided by green manuring and the large short-term economic losses associated with this practice are investigated for various rotations and patterns of herbicide use. This analysis is conducted using RIM, a bio-economic management model for ryegrass (Lolium rigidum).

Herbicide resistance has become a major problem in dryland agriculture. In Australia this particularly applies to annual ryegrass (Lolium rigidum) which has developed multiple resistance to a wide range of commonly used selective herbicides. Although herbicides are a very cost-effective means of reducing weed density, major changes to their use are required if sustainable weed management is to be achieved. In this study a model of ryegrass population dynamics was used to identify the best integrated weed management strategies and to evaluate changes in the economic payoff when choosing to conserve herbicides rather than exploit them rapidly. A situation of evolving herbicide resistance was simulated for a continuous wheat-lupin rotation and two cropping sequences including one and two pasture phases. Conservation of the last four shots of the selective herbicide Hoegrass was found to be less profitable than their exploitation. Nevertheless, conservation provided a better long-term weed control. Benefits from conservation were lower in a situation of reduced level of weed control, but appeared to increase with the inclusion of more pasture in the rotation.