Effect of fungicides applied after infection on the control of Mycosphaerella brassicicola on Brussels sprouts

Abstract

Ringspot caused by Mycosphaerella brassicicola was controlled on brussels sprouts, by applying a mixture of 2.5 g a.i. penconazole and 120 g a.i. mancozeb per 100 L either every 10- 14 days or only after identified infection periods. Applications after either 24 or 72 h of leaf wetness (9 or 5 applications) were as effective as 13 protectant applications and resulted in 19, 14 and 16% of sprouts being infected, respectively, compared with 95% of sprouts infected in unsprayed plots. Exposing potted plants to naturally dispersed inoculum, and 48 h of leaf wetness before spraying, showed that the fungicide mixture controlled ringspot when applied at either 2, 5 or 7 days after inoculation. Even when applied 14 or 21 days after inoculation, the number of infected leaves per plant, number of lesions per leaf and size of lesions were reduced compared with unsprayed plants. This curative effect was due to the penconazole component of the mixture. Exposing potted plants to naturally dispersed inoculum and leaf wetness periods of 24, 48 and 72 h showed that infection occurred within 24 h. At a mean temperature of 8¦C, the incubation period on cv. Victoria Long Island was 28 days.