Control of Phytophthora root rot in processing tomatoes by metalaxyl and fosetyl-Al

Abstract

The efficacies of metalaxyl and fosetyl-A1 were evaluated for the control of root rot in tomatoes (Lycopersicon esculentum Mill.) caused by Phytophthora nicotianae var. nicotianae in a greenhouse and in the field. In greenhouse experiments, disease severity was significantly (P<0.05) reduced with metalaxyl applied at rates of 1.5-25 g a.i./L as a soil drench and with fosetyl-A1 applied as a foliar spray at 3.2 g a.i./L. In the field, disease severity was reduced by applications of metalaxyl at rates up to 3 kg a.i./ha banded below the fertiliser at sowing and with additional applications to the bed shoulders at regular intervals for a period of 10 weeks after sowing. Metalaxyl treatments applied at sowing significantly reduced root rot severity for the first 12 weeks of crop development but failed to provide season-long protection. Yield of tomatoes at harvest was not significantly increased by the fungicide treatments, The use of metalaxyl granules in the field to control P. nicotianae root rot is not recommended.