FACTORS INFLUENCING ACTIVITY OF TRIAZOLE FUNGICIDES TOWARDS BOTRYTIS-CINEREA

The activity of triazole fungicides towards Botrytis cinerea was inves tigated in vitro (radial growth on fungicide-amended agar) and in vivo (foliar-sprayed tomato plants and dip-treated grapes). In both tests the benzimidazoles, benomyl and thiabendazole, and the dicarboximides, iprodione and vinclozolin, were used as reference fungicides. In all experiments benomyl and tebuconazole proved to be the most active fung icides. The transfer ratio, which is defined as the ratio between the EC(50) (the concentration inhibiting growth by 50%) of a particular fu ngicide determined in vivo and in vitro, was lowest for benomyl. The t ransfer ratio of tebuconazole was comparable to or lower than that of vinclozolin. Hence, no obvious correlation between in vitro and in viv o activity was observed. Field rates of tebuconazole recommended for c ontrol of B. cinerea are relatively low compared to those of benzimida zoles and dicarboximides. Tomato leaf homogenates and various biologic al compounds antagonized the activity of triazoles and dicarboximides but did not affect inhibitory potency of benzimidazoles. It is suggest ed that the factors mentioned account only partly for the limited fiel d performance of triazoles towards B. cinerea.