The effect of fungicides applied pre-stem extension on septoria tritici blotch and yield of winter wheat in Ireland

Ireland has the potential to produce some of the highest winter wheat yields in the world, however due to the highly disease conducive environment fungicides are heavily relied upon to achieve these yields. These fungicides primarily target control of septoria tritici blotch (STB), which if left untreated can result in significant reductions in yield. Typically winter wheat fungicide programmes are comprised of four applications, the first of which is applied pre-stem extension (PSE). It has been suggested that applying fungicides at this stage in the crops development slows disease progression to the upper canopy (final leaves three, two and one) which is responsible for the majority of yield potential. This study tested the effect of different pre-stem extension fungicide treatments on STB severity in the upper canopy during grain filling and subsequent grain yield in field trials conducted at three Irish locations over three consecutive growing seasons (2012-2014). When applied as part of a typical foliar fungicide programme significant differences in levels of STB on the final leaf three were observed at growth stage GS83between the PSE treatments (P = 0.05), with the solo azole resulting in higher levels of disease compared to the other fungicide treatments. Despite these differences in STB control no significant differences were observed between the treatments in final yield (P = 0.44). This study shows there is no yield advantage to applying fungicides prior to stem extension for control of STB, however, if they are being applied for the control of other disease e.g. yellow rust careful consideration should be taken with regards to choice of fungicide to avoid increasing STB severity later in the season.