Bull. Spec. CORESTA Symposium, Winston-Salem, 1982, p. 65, P07, ISSN.0525-6240

Evaluation of recent fungicides on the control of seed bed diseases of tobacco

NAGARAJAN K.; REDDY T.S.N.
Central Tobacco Research Institute (CTRI), Division of Plant Pathology, Rajahmundry (A.P.), India
In India, the most common endemic seed bed diseases on tobacco are damping off (Pythium aphanidermatum), black shank (Phytophthora parasitica f. nicotianae), and the frogeye spot (Cercospora nicotianae). These diseases together cause heavy damage during the nursery season, resulting in loss of healthy transplants. A replicated trial was conducted for two seasons to evaluate 15 fungicides (both systemic and contact) against these pathogens under artificial inoculation. Results indicated that three sprays of Metalaxyl (Ridomil 25 WP) at 0.05, 0.1, and 0.2% concentrations were outstanding in controlling both damping off and black shank. It had no effect on frogeye spot. Ridomil 5G and Apron seed treatment were ineffective against damping off, black shank, and frogeye spot. However, the combination of Ridomil 5G soil treatment followed by Ridomil 25 WP spray at 0.1% was found to be good in controlling damping off and black shank. Among the contact fungicides, eight sprays of Foltaf 80 WP, Fytolan 88 WP, Ziram 80 WP, Difolatan 80 WP at 0.2%, and Bordeaux mixture at 0.4% were effective in controlling all three diseases in seed beds, although they were inferior to three sprays of Metalaxyl at 0.1%. Maximum transplantable seedlings were obtained in treatments with Ridomil 25 WP at 0.05 and 0.1% spray, Ridomil 5G + Ridomil 25 WP at 0.1% spray, comac Parasol at 0.2%, Bordeaux mixture at 0.1%, and Difolatan 80 WP at 0.2%. There is so far no evidence of resistance by Pythium and Phytophthora to Metalaxyl under Rajahmundry conditions.