Variable rate application of fertiliser (VR) is a practice underpinning a profitable grains industry in Australia. We updated the extent of VR adoption through a national survey (n = 1 130) covering all grain growing regions. Three smaller regionalbased surveys (n = 39-102) collected detailed information on the nature and reasoning behind the use of various forms of the technology. We analysed the constraints to the adoption of each step using adoption theory. Surveys showed that 20% of grain growers have adopted some form of VR (varied from 11-35%), up significantly from \5% found 6 years earlier. Adopters are more than likely to have larger farms with a higher area in cropping. Many non-adopters were convinced of the agronomic and economic benefits of VR. A significant proportion of growers were managing within-field variability with manually-operated systems rather than more sophisticated VR technology, and have adopted some form of VR without yield maps, preferring to use soil tests, electro-magnetic induction or their own knowledge of soil and yield variation to define management. The rate of adoption is expected to continue to rise based on greater awareness of the benefits of the technology. The constraints to adoption were technical issues with equipment and software access to service provision and the incompatibility of equipment with existing farm operations.

Eradication is a management strategy that can provide substantial ecological and economic benefits by eliminating incursions of pest organisms. In contrast to eradication efforts that target other pests, weed eradication programs can be very protracted owing to the presence of persistent seed banks and difficulties in detecting the target. Hence there is a need to develop criteria to assist in the evaluation of progress towards eradication. Knowledge of the extent of a weed incursion (the 'delimitation' criterion) is considered fundamental for eradication success, as an incursion will progress from any infestations that remain undetected and thus uncontrolled. This criterion is examined with regard to eradication programs targeting Bassia scoparia L. A.J. Scott [= Kochia scoparia L. Schrader], Chondrilla juncea L. (both in Western Australia) and Orobanche ramosa L. in South Australia. The B. scoparia incursion, which has been eradicated, was largely delimited within 12 months of the inception of its eradication program. In contrast, the Western Australian C. juncea incursion has never been delimited, owing to insufficient investment in surveillance during an eradication program spanning 30 years. An exponential decrease in the detection ratio (infested area detected/area searched) over time suggests that delimitation has been approached within 6 years of the inception of the eradication program for O. ramosa . An effective surveillance program is essential for achieving delimitation of a weed incursion.

Because weed eradication programs commonly take 10 or more years to complete, there is a need to evaluate progress toward the eradication objective. We present a simple model, based on information that is readily obtainable, that assesses conformity to the delimitation and extirpation criteria for eradication. It is applied to the program currently targeting the annual parasitic weed, branched broomrape, in South Australia. The model consists of delimitation and extirpation (E) measures plotted against each other to form an ‘eradograph.’ Deviations from the ‘ideal’ eradograph plot can inform tactical responses, e.g., increases in survey and/or control effort. Infestations progress from the active phase to the monitoring phase when no plants have been detected for at least 12 mo. They revert to the active phase upon further detection of plants. We summarize this process for the invasion as a whole in a state-and-transition model. Using this model we demonstrate that the invasion is unlikely to be delimited unless the amount of newly detected infested area decreases, on average, by at least 50% per annum. As a result of control activities implemented, on average approximately 70% (range, 44 to 86%) of active infestations progressed to the monitoring phase in the year following their detection. Simulations suggest that increasing this rate of transition will not increase E to a significant extent. The rate of reversion of infestations from the monitoring phase to the active phase decreased logarithmically with time since last detection, but it is likely that lower rates of reversion would accelerate the trend toward extirpation. Program performance with respect to the delimitation criterion has been variable; performance with respect to the extirpation criterion would be improved considerably by the development and application of cost-effective methods for eliminating branched broomrape soil seed populations.

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