The effect of fungicide dose rate and mixtures on <i>Zymoseptoria tritici</i> in two cultivars of autumn sown wheat

Abstract

In the 2012-13 and 2013-14 seasons septoria tritici blotch (STB) caused by the fungal pathogen Zymoseptoria tritici was poorly controlled in autumn sown wheat in Canterbury. In 2014-15, a low disease pressure season, three trials were conducted to define the protectant and curative properties of two applications of triazole demethylation inhibitor inhibitor (DMI) and succinate dehydrogenase inhibitor (SDHI) fungicides for the control of STB at growth stage 31 and 39 on two cultivars of autumn sown wheat. The protectant activity of triazole and SDHI fungicides was more effective on the flag leaf than the curative activity on leaf two. The addition of an SDHI to a 75% fixed rate of triazole was more effective at controlling STB infection than triazoles alone. The addition of SDHI fungicides also significantly increased yield. The highest mean yields were achieved with the addition of a third application at GS65.