USE OF FUNGICIDES TO CONTROL CHOCOLATE SPOT (BOTRYTIS-FABAE) ON WINTER FIELD BEANS (VICIA-FABA)

Less chocolate spot (% leaf area affected) developed on winter-sown field beans sprayed with benomyl than on untreated beans or beans sprayed with iprodione, prochloraz or thiabendazole. A single benomyl spray during flowering reduced disease development and increased yield by 20% in 1982 when a severe chocolate spot epidemic developed in untreated plots during flowering. Benomyl sprays at flowering also increased yield in 1980 when there was less disease at flowering than in 1982, but did not increase yield in 1981 when there was little disease at flowering. In 1981 a severe chocolate spot epidemic developed early in the season and less chocolate spot developed on lower leaves of beans grown from seed treated with benomyl plus thiram than on beans grown from untreated seed. Treated plots yielded 70% more than untreated plots, although by early flowering there was no difference in chocolate spot between them. Seed treatment did not increase bean yields in 1982 and 1983, when chocolate spot did not develope early in the season. In the glasshouse, benomyl seed treatment prevented the development of aggressive lesions on lower leaves but thiram did not.