Three trials were carried out in the greenhouse and laboratory along with others in the field with the objective to study the effect of potassium phosphite with or without fungicides on the control of Phytophthora infestans in the tomato crop. Potassium phosphite at 300 g 100 L-1 with mancozeb application was more effective than products applied alone for the control of late blight of the tomatoes 'Rebeca' and 'Giuliana' on the 4th and 7th day after inoculation on leaf discs. In the field, clorotalonil/metalaxyl-M + mancozeb/propamocarb with potassium phosphite at 100, 200 and 300 g 100 L-1 were more effective than cymoxanil + mancozeb/fenamidone/iprovalicarb + propineb and potassium phosphite alone in the control of late blight. Dimetomorph + mancozeb + potassium phosphite drastically decreased the disease severity as compared with mancozeb, potassium phosphite alone or mancozeb + potassium phosphite. The mixture of mancozeb and potassium phosphite (300 g 100 L -1) provided greater control of late blight as compared to its use in isolation.
Solanum lycopersicum; Phytophthora infestans; phosphorous acid