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T. J. Gillespie
B. Srivastava
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R. E. Pitblado


A fungicide-spray scheduling scheme for tomatoes called TOM-CAST (tomato forecaster) was adapted for use with operational weather data in order to increase the number of users by eliminating the need for in-field measurements of hourly temperature and leaf wetness duration. Such schemes reduce cost, environmental risk, and the development of resistance to the fungicide. Duration of wetness was estimated as the length of time that the dewpoint depression (TTd ) remained between two specified limits, indicating the onset and offset of wetness. Several methods of obtaining the necessary temperature and dewpoint data were investigated. The preferred method, considering accuracy and simplicity, involved synthesis of hourly temperatures from locally observed daily maximum and minimum temperatures, and estimation of dewpoints from two Environment Canada hourly weather stations. With appropriate calibration, the scheme was able to match the number of sprays required by TOM-CAST exactly or within one spray.

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