Efficacy of Two Fungicides in Controlling Rhizoctonia Leaf Sheath Rot of Welsh Onion Caused by Rhizoctonia solani

Abstract

Leaf sheath rot caused by Rhizoctonia spp. is a widespread disease, and it causes serious damage to Welsh onion fields in Hokkaido, Japan. We evaluated the efficacy of two fungicides, i.e., tolclofos-methyl dust formulation and azoxystrobin flowable, against the disease in the field from 2013 to 2016. The fungicides were applied once or twice a year. Tolclofos-methyl dust formulation exhibited high efficacy with protective values of 100, 100 (in 2013); 85, 74 (in 2014); and 87, 100 (in 2016). Azoxystrobin flowable also exhibited high efficacy with protective values of 100, 100 (in 2013); 80, 88 (in 2014); 85 (in 2015); and 93 (in 2016) with one exception (26 in 2016). Therefore, both fungicides were found to be effective against Rhizoctonia leaf sheath rot in Welsh onion.