Efficacy of Trichoderma asperellum Seed Treatment and Ridomil® Application in Managing Late Blight on Potato

Potato seed tubers latently infected with Phytophthora infestans initiate late blight that requires early fungicide application raising economic and human concerns. The objective of the study was to determine the efficacy of Trichoderma asperellum seed treatment and Ridomil® (Metalaxyl 4% and Mancozeb 64%) application to manage late blight. Ridomil® was applied at 21-, 14- and 7-day intervals on seed tuber and apical cuttings pre-treated with T. asperellum at 33 % (3 × 106), 66% (7 × 106) and 100% (1 × 107 CFU/mL) concentration by either dipping or injection. Results revealed that 7- and 14-day spray intervals were not significantly different (P=0.05) in terms of yield and late blight severity. Rooted apical cuttings had 7.4% higher disease severity resulting in 2.3% lower yield than crop from seed tubers. T. asperellum at 66% and 100% concentrations reduced disease severity by 26% and 27% respectively. Pericardial injection had 8.3% higher yield and conversely 7.8% higher disease severity than dipping. The combination of T. asperellum at 66% concentration with a 14-day spray interval provided better late blight management. The results suggest that seed treatment by dipping using 66% T. asperellum suspension could increase fungicide application interval by 7 days while improving on yield.