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A Microcomputer-Based Instrument to Predict Primary Apple Scab Infection Periods. A. L. Jones, Professor, Department of Botany and Plant Pathology and Pesticide Research Center, Michigan State University, East Lansing, MI 48824. S. L. Lillevik and P. D. Fisher, Graduate Student and Professor, respectively, Department of Electrical Engineering and Systems Science; and T. C. Stebbins, Graduate Student, Department of Botany and Plant Pathology and Pesticide Research Center, Michigan State University, East Lansing, MI 48824. Plant Dis. 64:69-72. Accepted for publication 16 March 1979 . Copyright 1980 American Phytopathological Society. DOI: 10.1094/PD-64-69.

An electronic instrument was constructed to monitor temperature, leaf wetness, and relative humidity in apple orchards and was programmed to predict apple scab infection periods. It accurately predicted the minimum conditions for primary infection, as determined by disease development on small apple trees exposed to high densities of ascospore inoculum during eight wetting periods. The effects of relative humidities of ≥90% after wetting periods, the effects of sequential wetting periods, and Millsí table were used to make the predictions. The disease control obtained by eradicant schedules timed with the instrument and by protectant schedules applied at a standard time interval commonly used by apple growers did not differ significantly.

Keyword(s): epidemiology, Venturia inaequalis.