Herbicide efficacy in retained stubble systems

The GRDC project ‘Maintaining profitable farming systems with retained stubble - upper Eyre Peninsula’ aims to improve farm profitability while retaining stubble in farming systems on upper Eyre Peninsula (EP). One of the barriers to retaining stubble is the perceived reduction in pre-emergent herbicide effectiveness (efficacy) in stubbles. This component of the project is testing whether various stubble management activities impact on herbicide efficacy.Weed control in stubble retained systems can be compromised when stubbles and other plant residues intercept the herbicide and prevent it from reaching the desired target, or the herbicide is tightly bound to organic matter. Reduced herbicide efficacy in the presence of higher stubble loads is a particular issue for pre-emergence herbicides. Current farming practices have also changed weed behavior; eg prolonged dormancy in barley grass has been confirmed in many paddocks on Minnipa Agricultural Centre (MAC). As a part of the stubble project this trial was undertaken to assess herbicide efficacy in different stubble management systems.This article reports on the results of the third and final year of the trial. See EPFS Summaries 2015 and 2016 for previous trial reports.