International Symposium on Cereal Leaf Blights 2019 | University College Dublin, Ireland | 22-24 May 2019
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Ramularia leaf spot of barley (RLS), caused by the fungal pathogen Ramularia collo-cygni has the potential to reduce Irish winter and spring barley varieties by up 15%. Fungicides are currently the only effective and reliable means of control. Unfortunately the disease often only exhibits symptoms post-anthesis meaning decisions on control, such as product choice and/or application rate, must be made in the absence of disease levels or risk indicators. In most instances growers will be risk adverse and routinely apply fungicides to control RLS. Leaf surface wetness during stem extension has been tentatively suggested as a risk indicator for RLS. To assess if this can be used as means of determining risk and subsequently if RLS treatments can be tailored to reflect this risk, spring barley field trials were conducted at two locations in Ireland during the 2016-2018 seasons. Fortunately each season presented different levels of both predicted risk and disease levels. Depending on risk levels as determined by minutes of leaf wetness during stem extension, it was possible to reliably reduce fungicide spend by either reducing the dose or the number of modes of action without adversely impacting control of RLS. Throughout the study the multisite fungicide chlorothalonil remained central to control of RLS. Whilst additional modes of action are anticipated in the near future, given the ability of R. collo-cygni to adapt and develop fungicide resistance to single site fungicides, it is anticipated that the potential withdrawal of chlorothalonil from use within the European Union will have adverse impacts on control of RLS in Irish barley crops.