Ground Cover Supplement : GC Supplement - Foliar fungal diseases
15 FUNGICIDE RESISTANCE STRATEGY HEAVY RELIANCE ON A SINGLE MODE OF ACTION THREATENS THE LONG-TERM VIABILITY OF SEED AND FOLIAR FUNGICIDES "Greater fungicide use increases the risk of resistance, especially when fungicides with a single mode of action dominate the market for both seed treatments and foliar sprays. This is the case in Australia where the majority of fungicides, especially those used on cereals, are sterol demethylation inhibitor or DMIs such as triadimefon, propiconazole and flutriafol, all of which have the same mode of action. While fungicide resistance has not been confirmed in any pathogens of grain crops in Australia, there is a need to be forearmed as a number of key pathogens are considered at risk, due to the reliance on DMI fungicides and evidence from similar situations overseas." These conclusions, together with recommendations for future research and extension, were presented by Derek Hollomon, of the UK's University of Bristol, in a study commissioned by the GRDC. Experience elsewhere indicates that barley powdery mildew and botrytis are at high risk of developing resistance when a control strategy relies on DMI fungicides. Indeed, with similar treatment levels as in Australia, barley powdery mildew was found to develop resistance within three years in Europe. Other key pathogens considered at risk include Septoria tritici blotch, Septoria nodorum and net blotch, which in Europe have all seen a decline in control with DMI fungicides over time. For some pathogens such as Septoria tritici and yellow leaf spot, resistance to the strobilurin fungicides has developed more rapidly. However, leaf, stem and stripe-rust pathogens have been found to have a low resistance risk to DMI fungicides, which offer effective control of rust, especially when used as a strategic preventative spraying program. The situation in pulses is a little better with fungicides from several different modes of action groups registered for many of the key pulse crops. While seed treatments containing thiram and sprays based on chlorothalonil and mancozeb are all-protectant, muti-site inhibitors, with a low risk of resistance, the single-site foliar fungicides carbendazim, procymidone and metalaxyl all have a high risk of resistance. The report recognises the importance of using a three-pronged strategy for disease prevention and control; that is, the use of plant breeding to produce more resistant varieties, cultural controls, including rotation and variety choice and removing the green bridge, and the strategic use of fungicides. To help ensure the value from current and future fungicides the report outlined several areas for the GRDC to focus its investments. These include: evidence of fungicide sensitivity; the introduction of fungicides with additional modes of action; maintenance of plant-breeding programs; and support to improve grower awareness of fungicide-resistance issues. The GRDC will address these issues in future investment programs. GRDC Research Code UBR00001 More information: Dr Rohan Rainbow, Manager Crop Protection, GRDC, 02 6166 4500, firstname.lastname@example.org FUNGICIDES FOLIAR FUNGAL DISEASES GROUND COVER Barley leaf disease management options FOLIAR FUNGICIDES PROVIDE SUPERIOR CONTROL OF BARLEY LEAF RUST IN TRIALS IN WESTERN AUSTRALIA FUNGICIDE USE FOR wheat diseases is becoming more widely understood, while the situation in barley still requires better definition. Five years of trials by Dr Kith Jayasena, from the Department of Agriculture and Food, Western Australia (DAFWA), and colleagues at Precision Agronomics Australia (PAA), carried out in south-west WA, are helping to provide more details. This work focused on barley leaf rust, which was found to cause significant and regular yield losses across the seven experiments run over five years along the south coast of WA. Left untreated, barley leaf rust caused average yield losses of about 33 per cent, with higher losses in extreme disease situations. In two DAFWA experiments foliar fungicide applications provided significantly better control of barley leaf rust, and consequently yield, compared with fungicides applied in-furrow (Triad® (triadimefon)), or as seed dressing (Baytan® (triadimenol), Jockey® (fluquinconazole)) at label rates. An experiment conducted by PAA under severe early rust pressure at Coomalbidgup in 2006 revealed that a GS31 application of Amistar® Xtra (cyproconazole and azoxystrobin), Tilt® Xtra (cyproconazole and propiconazole), Opus® (epoxiconazole) and Folicur® (tebuconazole) gave good immediate control of leaf rust on GairdnerA barley. Longer periods of protection were provided by higher rates and Amistar® Xtra was most effective, providing up to 31 days protection at the 400 millilitres a hectare rate. Yield and quality improvements reflected disease control assessments. A second application of fungicide at grain fill provided additional yield response, which was reflected in gross margins depending on the effectiveness of the initial treatment. Opus®, Folicur®, Tilt® Xtra and Amistar® Xtra provided yield responses, but the higher rate of Amistar® Xtra gave the greatest yield response and best gross margin response as this was the only treatment to meet malting quality. Barley leaf rust is an aggressive and difficult foliar disease to control, but the use of foliar fungicides including products such as Amistar® Xtra, from the stobulurin group, do provide vastly improved levels of barley leaf rust control over seeding-applied fungicide. In addition to yield benefits, grain quality was improved with large reductions in screenings and improved grain colour, all positive for achieving malt barley on a more regular basis.
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