Control of late blight in potato by full and reduced rates of oxadixyl mixtures

The effect of oxadixyl-based fungicidal mixtures on the development of late blight and the buildup of resistance of Phytophthora infestans to oxadixyl was studied in potato crops (cv. Alpha) grown in plastic houses. Half-rates of SAN 518F (mancozeb + oxadixyl) applied weekly provided better disease control and reduced resistance buildup more effectively than the full rates of the mixture applied biweekly. Mancozeb applied weekly at full rate was less effective than SAN 518F at half-rate. The data suggest that lowering the dosage together with shortening the interval between sprays is an efficient strategy to combat mixed populations - sensitive and resistant to phenylamides - of P. infestans when phenylamide-based fungicidal sprays are used.