Ground Cover Supplement : GC Supplement - Cereal foliar fungal diseases
19 Southern region SEPTORIA FUNGICIDE RESISTANCE DETECTED Septoria tritici blotch has increased in importance in high-rainfall areas of the southern grdc region and careful attention to fungicide strategies is required to minimise the chances of further resistance developing By dr andrew milgate PARTIAL RESISTANCE IN Septoria tritici blotch (STB) to some azole fungicides has been detected in Australia through research at the New South Wales Department of Primary Industries. This is the first instance of fungicide resistance in a wheat disease in Australia. While the resistance might not yet be causing reduced spray efficacy, it is vital that a strategy to prolong fungicide effectiveness is adopted. The two mutations identified affect the efficacy of several azole fungicides (Group 3) commonly used in Australia such as triadimefon, triadimenol, tebuconazole, propiconazole and epoxiconazole (which is not registered for control of STB in Australia). The mutations reduce the effectiveness of these fungicides rather than making them completely ineffective. However, if the fungicides continue to be used, further selection pressure will be applied to the pathogen and new and more concerning mutations will potentially be selected. It is critical that growers adopt strategies to reduce the selection rate of further mutations and therefore extend the useful life of available fungicides. To achieve this, growers are encouraged to mix or alternate different azoles. This is because not all azole fungicides are affected equally by mutations of the STB fungus. Products that combine azoles, such as Tilt® Xtra (propiconazole and cyproconazole) or Impact Topguard® (tebuconazole and flutriafol), and have a registration for STB, could be used in this way. In crops where two fungicide applications are required (for example, at GS31 and GS39) it is important not to use the same active for both applications. Always follow label guidelines and adhere to all maximum residue limits. In Australia, there is a limited choice of fungicides with different modes of action for use on wheat. PHOTOS: ANDREW MILGATE Several products combine a strobilurin with an azole and these may provide some benefits in delaying or reducing the risk of resistance development. However, on their own, the strobilurins are considered to be at high risk of developing resistance due to their single-site mode of action. In some countries, resistance to strobilurins is so widespread in the STB population they are no longer recommended as effective control measures, even in mixtures. In addition to mixing and rotating of fungicides, an integrated approach to disease control that includes crop rotation and avoidance of susceptible cultivars will reduce inoculum loads, and therefore reduce the likelihood of resistance to fungicides developing. □ grdc research code dan00177 more information: Dr Andrew Milgate, NSW DPI, 02 6938 1990, firstname.lastname@example.org Septoria tritici blotch with resistance to several azole fungicides (Group 3) has been identified for the first time in Australia. NSW DPI plant pathologist Dr Andrew Milgate (pictured) says if the fungicides continue to be used, further selection pressure will be applied to the pathogen and potentially new and more concerning mutations will be selected.
GC Supplement - Frost
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