A long run programming model for analysing investment behaviour on perennial crop farms is formulated and applied to citrus and wine grape producing farms in the Murumbidgee Irrigation Area. Prices and technological parameters are defined exogenously, while the optimal replanting pattern of the crops and the optimal mix of irrigation techniques are determined endogenously. The model is used to examine likely investment in water saving irrigation technology at different crop prices and input costs. The results indicate that such investment is a profitable option at current water charges, particularly for those farmers with access to off-farm employment However, the adoption decision will be highly sensitive to potential cost savings. Water-saving technology could become more attractive under higher water charges, but only if the preferred option of farm expansion were not available. The modelling framework, which allows for control over many factors influencing perennial crop investment decisions' has applications in the analysis of the long term consequences of many policy options affecting farm yields or prices.