Fungicide control of ringspot (Mycosphaerella brassicicola) in Brussels sprouts

Abstract

A population of Mycosphaerella brassicicola insensitive to carbendazim (a benzimidazole fungicide) has developed in the main brussels sprouts (Brassica oleracea var. gemmifera) growing area of South Australia. This was evident in a fungicide evaluation experiment in 1986 where ringspot developed despite 9 applications of carbendazim (250 mg a.i./L) on a 10-14-day schedule, whereas in the same area 4 benomyl applications (250 mg a.i./L) on a 21- day schedule controlled the disease in 1970. In 1986, other fungicides such as the protectant chlorothalonil (800 mg a.i./L), and the systemics fenarimol (37.5 mg a.i./L), penconazole (25 mg a.i./L) and triadimefon (125 mg a.i./L) controlled the benzimidazole insensitive strain when applied every 10-14 days. On sprayed plants, fewer than 3 ringspot lesions developed on infected mature leaves, whereas on unsprayed and carbendazim treated plants, more than 100 lesions per leaf developed by the final harvest. Total yield of sprouts was significantly reduced (P = 0.05) in unsprayed plants and half of these were unmarketable compared with more than 80% of the sprouts being marketable in most of the sprayed plots.