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Rainfall Thresholds as Support for Timing Fungicide Applications in the Control of Potato Late Blight in Ecuador and Peru

February 2009 , Volume 93 , Number  2
Pages  142 - 148

Peter Kromann, Department of Plant Biology, Faculty of Life Sciences, University of Copenhagen, Thorvaldsensvej 40, Dk-1871 Frederiksberg C, Denmark, and International Potato Center (CIP), P.O. Box 17-21-1977, Quito, Ecuador; Arturo Taipe, CIP, Quito, Ecuador; and Willmer G. Perez and Gregory A. Forbes, CIP, P.O. Box 1558, Lima 12, Peru

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Accepted for publication 5 September 2008.

Accumulated rainfall thresholds were studied in seven field experiments conducted in Ecuador and Peru for their value in timing applications of fungicide to control potato late blight, caused by Phytophthora infestans. Fungicide regimes based on accumulated rainfall thresholds ranging from 10 to 70 mm were compared with calendar spray schemes of every 5 or 7 days. Very low thresholds of 10 to 20 mm gave similar levels of control and resulted in similar number of sprays as did calendar spraying. However, neither low thresholds nor calendar sprays were effective in protecting susceptible potato genotypes in over half of the experiments. Thresholds of 25 to 50 mm of rainfall led to reduction in the number of sprays needed to protect resistant cultivars but also resulted in high levels of disease on susceptible cultivars. We conclude that timing fungicide sprays based on accumulated rainfall thresholds could be a successful component of integrated management strategies that include cultivars with moderate or high levels of resistance. The simplicity of measuring accumulated rainfall means that the technology can potentially be used by resource-poor farmers in developing countries.

Additional keywords:knapsack sprayer, mancozeb

© 2009 The American Phytopathological Society