Yield reduction and losses due to tuber infection caused by potato late blight

In exact field trials conducted during 1997-2000 yield losses and losses du e to tuber infection caused by late blight were observed in Lukava and Dali potato varieties. Sets of untreated variants, variants treated with differ ent fungicides used for the whole season, various fungicide programs and ec ological treatments (copper preparations, max. 3 kg Cu.ha(-1)) were investi gated. 5-7 treatments were applied in fungicide variants, in case of ecolog ical treatments 2-4 sprays were applied per season. Occurrence of foliage d isease was very strong in experimental years; conditions for tuber infectio n were only suitable in 2000. Total haulm destruction of untreated crop occ urred in 27-38 days from the first blight symptoms, tuber yield reached 19. 04-35.4 t.ha(-1). Individually applied fungicides increased yield about 2-1 15%, fungicide programs about 13-106% and ecological treatments about 0-18% compared to untreated variant. Tuber infection was 0-1.2% in all trial var iants in 1997-1998, tubers were not infected by late blight in 1999. 35.7% of tubers were infected in untreated variant, 7.44-54.74% of tubers in fung icide variants and 7.69-37.3% of tubers in fungicide programs in 2000. 30-5 4.74% of tubers were infected in ecological treatments. Infected tubers wer e distributed in soil prior to harvest that year and they significantly red uced final yield. Losses caused by late blight are very serious, but they c ould not be predicted and generalized for respective year. They are set by weather conditions, which affect disease occurrence, characteristics of use d variety and protection system. Trial results proved economic importance o f late blight and decisive effect of chemical protection on reducing yield and qualitative losses.