Effectiveness of several fungicides on white rot of the spring crop Welsh onion by drench application to plug seedlings

This study investigated the efficacy of drench application of several fungicides to plug seedlings to control white rot, a difficult to control disease, of the spring crop Welsh onion (Allium fistulosum L.) caused by Sclerotium cepivorum Berkeley in fields without soil disinfection. Four fungicides, penthiopyrad, pyraziflumid, inpyrfluxam, and mandestrobin, were tested. Of the Welsh onions grown year-round by ridging, the spring crop Welsh onion has a period of more than 2 months from fixed planting to the onset of infection. However, once infected, it is the most susceptible of all cropping types to white rot because the optimum period for disease development is approximately 6 months until harvest. Among the four fungicides, pyraziflumid solution dissolved up to 100 times in water demonstrated excellent control of white rot on the Welsh onion by drench application to plug seedlings. After drench application to plug seedlings, sufficient amounts of pyraziflumid were maintained at the optimum infection stage in the leaf sheaths and near the sheath joints of the Welsh onion to suppress infection by S. cepivorum.