To investigate whether a break crop can be used to manage weeds.

• Wheat grain yield can be expected to be reduced by around 0.5 t/ha for every tonne of in-crop grass weed dry matter present in spring.
• Wheat following break crops were consistently more profitable than wheat on wheat. This in part reflected the  relatively low wheat grain prices experienced during experimentation, and the high returns for canola, but was also related to the efficacy and costs of ryegrass control.
• Growing pulses for brown manure (Bm) lost money in the year that they were grown, but achieved excellent weed control, provided high inputs of N and a residual carry-over of soil water, and more ground cover than if they had been cut for hay.
• In the presence of a high density of herbicide resistant ryegrass a ‘single break’ was not adequate to reduce weed seedbanks and subsequent in-crop weed competition. ‘Double breaks’ (two broad leaf break crops, or break crop - cereal hay sequence) reduced ryegrass seedbank numbers to manageable levels and were amongst the most profitable sequences.
• Break crop choice and selection should be based on individual farm management and ability to manage the various break crops options in the rotation. If growers remain flexible in break crop and end-use decisions, and make suitable choices, risks associated with producing them can be greatly reduced.
• A cropping program that includes break crops is likely to be more sustainable in terms of N inputs and risk of build-up of root diseases than continuous wheat, and provided cheaper, more effective strategies for controlling herbicide resistant grass weeds.