Extension programs to encourage farmers to reduce reliance on herbicides by adopting integrated weed management (IWM) practices have met with limited success. Studies aiming to understand the factors that influence farmers' choices of integrated control practices have faced difficulties in variable specification, and have not achieved high explanatory power. Using data from grain growers in Western Australia, where herbicide resistance in major crop weeds is common, this study tests the applicability of a framework for the IWM adoption decision in which herbicide efficacy is assumed to be a potentially exhaustible resource. Farmers' perceptions of multiple techniques and other variables are aggregated using principal components, and used in logistic regressions to explain the intensity of use of IWM practices. Eighty-six percent of growers were correctly classified according to use of multiple IWM practices. Herbicide resistance and expectations of the future availability of effective new herbicides were significant in explaining IWM adoption. IWM adoption and herbicide-resistance management are shown to be information-intensive and involving an intertemporal resource management decision. Copyright 2007 International Association of Agricultural Economists.

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This article claims to do three things. First, develop a formula for measuring size of research benefits which is generally applicable to all types of supply shift. Second, use this formula to assess the possible error involved in previous studies employing alternative equations. Third, initiate discussion on variables which might influence the type of supply shift. The article concludes that uncritical application of previously developed formulas without regard to the type of supply shift can result in substantial bias in estimates of research benefits. The implication is that calculation of rates of return on agricultural investment may also be severely biased.

Greater adoption of integrated weed management, to reduce herbicide reliance, is an objective of many research and extension programmes. In Australian grain-growing regions, integrated weed management is particularly important for the management of herbicide resistance in weeds. In this study, survey data from personal interviews with 132 Western Australian grain growers are used to characterise the use and perceptions of integrated weed management practices. The main objective was to identify opportunities for improved weed management decision making, through targeted research and extension. The extent to which integrated weed management practices are used on individual farms was measured. Perceptions of the efficacy and reliability of various weed management practices were elicited for control of annual ryegrass (Lolium rigidum Gaud.), along with perceptions of the economic value of integrated weed management practices relative to selective herbicides. All growers were shown to be using several integrated weed management practices, although the use of some practices was strongly associated with the presence of a herbicide-resistant weed population. In general, both users and non-users were found to have high levels of awareness of integrated weed management practices and their weed control efficacy. Herbicide-based practices were perceived to be the most cost-effective. Opportunities for greater adoption of integrated weed management practices, to conserve the existing herbicide resource, exist where practices can be shown to offer greater shorter-term economic value, not necessarily just in terms of weed control, but to the broader farming system.

Some hypotheses about the timing of farmers becoming aware of an innovation and the subsequent decision to use that innovation are derived from a recentlydeveloped, decision-theoretic model of the adoption process. They are tested using empirical evidence on the time taken by early adopters of trace element fertilisers in S.A. to discover and decide lo use this innovation. The central role of information search in the adoption process is emphasised and it is postulated that various distance measures provide a useful measure of information availability and reliability. The results of the empirical analysis are consistent with the hypothesised relationships. Another finding is the importance of distinguishing between early adopters who are genuinely innovative, and those potential later adopters who adopt early because they happen, by chance, to operate a farm in close proximity to another early adopter. IntroductionThe subject of this paper is the factors affecting inter-firm variability in the timing of the discovery, and subsequent decision to first use, an 'off-the-shelf agricultural process innovation (the adoption decision). In particular, attention is paid to the effect of distance to information source on the timing of these decisions. Jones (1967) and Rogers and Shoemaker (1971) have reviewed the considerable number of empirical studies that have been conducted in an attempt to 'explain' individual variability in the timing of the adoption decision. Most have been able to account for only 50 per cent or less of the variance in the dependent variable, and they have often reached conflicting conclusions about the importance and/or direction of the effect of various explanatory variables. In part, these poor results can be attributed to omitted variables, especially those capturing locational considerations. They also reflect the lack of a satisfactory conceptual framework on which to base empirical analysis of the adoption decision. For instance, notwithstanding frequent suggestions in the literature that the adoption process comprises several stages, Rogers and Shoemaker (1971, p. 350) cite many hundreds of attempts to account empirically for variation in timing of individual adoption decisions, but only six which attempt to relate it to measured duration of one or more of the above stages. A simpler approach to defining adoption stages is likely to help remedy this situation.A theoretical model of the adoption process, in which a central role is assigned to information search as the prime determinant of duration of * Presently at the University of Minnesota.