Optimising control of an agricultural weed in sheep-production pastures

Optimal integrated control strategies for the weed blackberry (Rubus anglocandicans) infesting sheep pastures in Australia are analysed for a range of different circumstances. A wide range of control strategies with moderate to high costs and efficacies are analysed, including chemicals, mowing, grazing goats and biological control. The study employs a stochastic dynamic simulation model and a stochastic dynamic programming model to find the optimal control strategies under different levels of infestation. Results show that the application of a biological control agent (Phragmidium violaceum) increases expected net present value (ENPV) by so little that it is not worth introducing. Results indicate that for higher initial infestation areas, the optimal control strategies include fewer control options, resulting in lower cost but also less effective control. This is because the control costs are proportional to the infestation area, so applying expensive control strategies in high infestation area has lower net benefits. When the labour cost of spraying chemicals increases and infestation area is high, it is optimal to replace chemicals with mowing. If the efficacy of chemicals increases it is optimal to use less effective and cheaper chemicals.