Reducing Claviceps purpurea sclerotia germination with soil-applied fungicides

Ergot, caused by the fungus Claviceps purpurea, is an important seed replacement disease of perennial ryegrass (Lolium perenne L.) grown for seed in the U.S. Pacific Northwest. Current management efforts rely on multiple fungicide applications to protect flowers from airborne ascospores during anthesis, but protective fungicide applications often provide incomplete control. Applications of fungicides to the soil, with the goal of preventing or reducing sclerotia germination, can potentially reduce the amount of ascospores and primary inoculum available in the spring. Use of fungicides applied to soil to reduce sclerotia germination were compared in two in-vitro and three field experiments. Out of eight fungicides, azoxystrobin + propiconazole and picoxystrobin + cyproconazole reduced sclerotia germination and capitula formation in both laboratory trials, whereas fluopyram + prothioconazole significantly reduced sclerotia germination and capitula formation in only one laboratory experiment. Five fungicides were applied in fall, spring, and both seasons in artificially infested field plots in 2014, 2015, and 2016. Fall applications of fluopyram + prothioconazole reduced area under capitula production curve (AUCPC) values by 59, 72, and 73% in 2014, 2015, and 2016, respectively. Azoxystrobin, azoxystrobin + propiconazole, and pyraclostrobin, reduced AUCPC values by 34-42% over three years of field trials. These results suggest that soil-applied fungicides can significantly reduce sclerotia germination and capitula production by C. purpurea and offer the potential to disrupt the ergot disease cycle in perennial cool-season grass seed production systems.