Evaluation of the TOM-CAST Forecasting Model in Asparagus for Management of Stemphylium Leaf Spot in Ontario, Canada

Plant Disease
Jennifer M Foster, Mary Ruth McDonald

Abstract

In the last 5 years, asparagus acreage in Canada has increased by over 25%. Stemphylium leaf spot, caused by Stemphylium vesicarium, has emerged as the predominant foliar pathogen of asparagus. Typically, contact fungicides are applied every 14 days; however, regardless of the number of applications, growers are not achieving adequate control of the disease. The TOM-CAST forecasting model is used widely in Michigan asparagus fields, but it has never been assessed for suitability in Ontario or in the popular cultivar, Guelph Millennium. Six field trials were conducted in 2012 and 2013 to evaluate the TOM-CAST forecasting model in two asparagus cultivars. The fungicides chlorothalonil or azoxystrobin/difenoconazole were applied according to the forecasting model or on a 14-day interval. The effectiveness of the forecasting model differed between sites and cultivars. Even though TOM-CAST is used in all cultivars in Michigan, TOM-CAST was not effective on Guelph Millennium. In the cultivar Jersey Giant, however, TOM-CAST with a 20 disease severity value spray interval improved control of Stemphylium leaf spot without increasing the number of sprays, compared with a 14-day treatment. The results in Guelph Millennium differed between...Continue Reading

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