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). Weed control in stubble retained systems can be compromised when stubbles and organic 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 dormancy in barley grass genotypes in many paddocks on Minnipa Agricultural Centre (MAC).As a part of the stubble project this trial was undertaken to assess herbicide efficacy (effectiveness) in different stubble management systems. To understand how herbicides perform it is important to know the properties of the herbicide, the soil type and how the herbicide is broken down in the environment. The availability of a herbicide is an interaction between the solubility of a herbicide, how tightly it is bound to soil particles and organic matter, soil structure, cation exchange capacity and pH, herbicide volatility, soil water content and the rate of herbicide applied (EPFS Summary 2015, p132).This article reports on the results of the second year of the trial, with a third year of the trial to be conducted in 2017.