Herbicide resistance has become a major problem in Australian dryland agriculture. This situation has resulted from the repeated use of herbicides in place of the traditional weed control provided by cultivation and grazing. Farmers have addressed the problem of herbicide resistance by adopting a system of integrated weed management that allows weed control with a range of different techniques and herbicides. One of the non-chemical methods being considered by farmers is “green manuring”, which involves ploughing a healthy growing crop or pasture into the soil in order to prevent weed seed production and provide other benefits. In this study, the trade-offs between the effective weed control and biological benefits provided by green manuring and the large short-term economic losses associated with this practice are investigated for various rotations and patterns of herbicide use. This analysis is conducted using RIM, a bio-economic management model for ryegrass (Lolium rigidum).