Use of lucerne (Medicago sativa L.) pastures in crop rotations has been proposed as a method to enhance weed management options for growers facing herbicide resistance in Western Australia. An existing model for analysing herbicide resistance in the important crop weed annual ryegrass (Lolium rigidum Gaud.) is consequently extended to include lucerne, used for grazing by a sheep enterprise. Seven rotational options are analysed, including various combinations of lucerne, annual pastures, and crops. Lucerne provides additional weed management benefits across the rotation, but in the region studied these benefits are only sufficient to make lucerne rotations the most profitable option in situations where ryegrass is resistant to multiple herbicide groups, and/or livestock prices are very high. Key words. Herbicide resistance, integrated weed management, economics, weed population dynamics.