Efficacy of spot form of net blotch suppression in barley from seed, fertiliser and foliar applied fungicides

Spot form of net blotch (SFNB), caused by Pyrenophora teres f. maculata is a prevalent and damaging foliar disease of barley (Hordeum vulgare). Fungicides are commonly used to manage SFNB infection and reduce production loss in susceptible varieties. This study determined the efficacy of suppression of SFNB and associated grain yield and quality improvements from application of fungicides to seed, fertiliser and/or foliar treatments. Eight field experiments were conducted in south-eastern Australia during 2016-2018. Two experiments compared single applications of different commercially available seed, fertiliser and foliar fungicides. Six experiments evaluated different growth stage application timings of either a single application or combinations of seed applied fluxapyroxad and foliar applied prothioconazole + tebuconazole. Spot form of net blotch caused grain yield loss of up to 1.2 t/ha (20%), reduced grain retention (percentage seed width greater than 2.5 mm) and weight by up to 15% and 13%, respectively, and increased screenings (percentage seed width less than 2.2 mm) by up to 18%. Seed applied fluxapyroxad was the most effective fungicide treatment providing the greatest SFNB suppression, grain yield and quality increase of the single fungicide applications. The combination of seed applied fluxapyroxad with a foliar application of prothioconazole + tebuconazole at flag leaf emergence significantly increased grain yield and quality further in one experiment. The dual foliar fungicide application of prothioconazole + tebuconazole at stem elongation (Z31) and flag leaf emergence (Z39) was not as effective in providing SFNB suppression according to AUDPC but provided comparable grain yield and quality to the seed and foliar treatment. Of the foliar fungicides, prothioconazole + tebuconazole and bixafen + prothioconazole provided the best SFNB suppression, grain yield and quality. These fungicide applications strategies provide improved SFNB management options for barley growers, particularly in high yielding crops where grain yield exceeds 5 t/ha.