The figure is the work of scientists in the Farm Systems team at AgResearch and is based on the development of a robust new method for quantifying the economic losses attributable to pasture weeds.
The scientists developed the “seasonal pattern” model primarily for Californian thistle (Cirsium arvense) but it is applicable to any weed species that exhibits a seasonal pattern in its pasture occupancy.
The work has just been accepted for publication in Weed Research, an international journal of weed biology, ecology and vegetation management.
Lead author Dr Graeme Bourdôt says researchers can now use this new model for accurate economic analyses for Californian thistle at various scales.
“We applied the model at the national scale, scaling it using farmer estimates of peak whole-farm cover to derive mean monthly covers, and then mean annual percentage covers of the weed for dairy, beef, sheep/beef, sheep and deer farms. The percentage of pasture lost, in combination with 2011-12 farm statistics, revealed that Californian thistle caused a national loss in pastoral farm gross revenue in 2011-12 of $685million ($446m dairy, $233m sheep/beef, $6m deer).
Dr Bourdôt says that at the scale of a particular farm, in conjunction with a single point-in-time estimate of the weed’s cover on the farm, the expected cover of the weed on for each month of the year can be determined.
“These estimates can then be used in a farm system model such as Farmax, to explore the impact of the thistle and compare the economics of alternative management methods.”
Dr Bourdôt says that previous estimates of economic cost of California thistle (and of pasture weeds in general) have been based on either anecdote or single point-in-time estimates of the weed’s occupancy that do not account for the seasonal dynamics of the weed in a pasture nor the changing feed value of the pasture over the year.