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Influence of Physiological Age of Pima Cotton on the Need for Fungicide Treatment to Suppress Alternaria Leaf Spot. D. Shtienberg, Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet-Dagan 50250, Israel; Y. Kremer(2), and A. Dinoor(3). (2)(3)Department of Plant Pathology and Microbiology, Faculty of Agriculture, P.O. Box 12, Rehovot 76100, Israel. Phytopathology 83:1235-1239. Accepted for publication 28 June 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-1235.

Field and controlled-environment trials were conducted to develop concepts for integrating age-related resistance and fungicides in the management of Alternaria macrospora, the causal agent of Alternaria leaf spot of Pima cotton. The influence of physiological age of the crop and of the individual leaves on infection incidence and on the rate of lesion expansion was examined on leaves sampled from the field. Both components increased with the physiological age of individual leaves but were not affected by the age of the crop. The effects of age-related resistance on the need for fungicide treatment were examined in two trials in 1990 and 1991. The efficacy of maneb applied in a 10- or 14-day schedule relative to weekly maneb applications decreased with crop age, while relative control efficacy of tebuconazole applied in a 10-, 14-, 17- or 21-day schedule did not change. It was concluded that the type of fungicide and the frequency of application should be determined by the age-related response of the host plant to the pathogen.

Additional keywords: control, epidemiology, IPM.