1Central Potato Research Station, Ooty, 643004, T.N.
Soil Microbiology and Pesticides Laboratory, Department of Botany, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad, 431004, M.S.
Sensitivity of 100 Phytophthora infestans (Mont.) De Baiy isolates against metalaxyl was studied by floating leaf disc technique. Of these 82% isolates were most sensitive, 5% were moderately sensitive, 4% were resistant, 5% were moderately resistant while 4% were highly resistant. Fungicides like SAN- 518, chlorothalonil, mancozcb, akomin and phytoalexin were used in combination with metalaxyl on seven wild metalaxyl resistant and three sensitive isolates. Percentage control efficacy (PCE) of metalaxyl with all the five fungicides was 100% on sensitive isolates even at lower concentrations. PCE on resistant isolates, however ranged from 84 to 100%. Use of metalaxyl in mixture with chlorothalonil was highly effective (PCE 100%) followed by SAN- 518 (PCE 99%), akomin (PCE 96%), phytoalexin (PCE 96%) and mancozeb (PCE 85%) in decreasing order.
