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Potato Late-Blight Management in the Toluca Valley: Forecasts and Resistant Cultivars

    Authors and Affiliations
    • Niklaus J. Grünwald , Cornell-Eastern Europe-Mexico (CEEM) Potato Late Blight Project, c/o PICTIPAPA, Conjunto Sedagro, Metepec, Edo. de México 52142, México and Department of Plant Pathology, Cornell University, Ithaca, NY 14853
    • Oswaldo A. Rubio-Covarrubias , Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias (INIFAP), Conjunto Sedagro, Metepec, Edo. de México 52142, México
    • William E. Fry , Department of Plant Pathology, Cornell University

      Published Online:

      We evaluated host resistance and fungicide forecasting as components of integrated management in the Toluca Valley of central Mexico. Potato cvs. Rosita and Norteña showed high levels of resistance (20 and 4% final disease severity, respectively) in the no-spray controls, whereas susceptible cv. Alpha was at 90% defoliation well before the end of the season. Disease on Alpha was well managed with a weekly spray of chlorothalonil. None of three published forecast systems was entirely appropriate for this pathosystem. SIM-CAST accurately allocated fungicide for a susceptible cultivar but needs to be adapted for the high level of resistance of Rosita and Norteña. TOM-CAST and BLITECAST did not recommend the initial fungicide application until after disease was well established in the plots. We believe that the low-temperature response of Phytophthora infestans needs to be reevaluated for the highland tropics.