Straw and living mulches compared with herbicide for under-vine weed control in a Public-Private Benefit Framework

A common practice in Australian vineyards is to manage under-vine weeds with approved herbicides applied one or more times each year. A current project is testing the potentials in a range of pasture species and cereal straw as under-vine mulches compared with herbicides for weed control. Grass and legume pasture species in under-vine trials in 2015-16 have shown promising results at some sites, with grape yields in some cases exceeding those of the herbicide control plots. Weeds compete with vines for water and nutrients and may provide a ‘green bridge’ between seasons, hosting pests and pathogens below the vines. Among the problems with repeated use of herbicides is the evolution of resistant populations of weeds, and their spread within the vineyard and to neighbouring properties and public lands. This study subtracts the costs of typical herbicide regimes and those of alternative mulches and other operational vineyard costs from the values of their respective grape yields, as baseline prices and yields vary over time, to define the distribution of Gross Margins for each treatment. Further subtracting the manager’s living costs, annual overheads, interest and taxes for random 10-year samples of simulated yields and prices allows estimation of long-term distributions of decadal cash balances for each under-vine treatment. Showing the probabilities of vineyard financial viability, these are private financial risk profiles for each treatment, differing by location. Juxtaposing these with the value of reduced risk of herbicide-resistant weed seed spreading beyond the vineyard permits analysis in a Public-Private Benefit Framework.