Disease Risk Forecasting with Bayesian Learning Networks: Application to Grape Powdery Mildew (Erysiphe necator) in Vineyards

Weixun Lu,Alex J Cannon,Nathaniel K Newlands,David E Atkinson,Odile Carisse

doi:10.3390/agronomy10050622

Abstract

Powdery mildew (Erysiphe necator) is a fungal disease causing significant loss of grape yield in commercial vineyards. The rate of development of this disease varies annually and is driven by complex interactions between the pathogen, its host, and environmental conditions. The long term impacts of weather and climate variability on disease development is not well understood, making the development of efficient and durable strategies for disease management challenging, especially under northern conditions. We present a probabilistic, Bayesian learning network model to explore the complex causal interactions between environment, pathogen, and host for three different susceptible northern grape cultivars in Quebec, Canada. This approach combines environmental (weather, climate), pathogen (development stages), and host (crop cultivar-specific susceptibility) factors. The model is evaluated in an operational forecast mode with supervised and algorithm model learning and integrating Global Forecast System (GFS) Ensemble Reforecasts (GEFSR). A model-guided fungicide spray strategy is validated for guiding spray decisions up to 6 days with a 10-day forecast of potential spray efficacy under rain washed off conditions. The model-guided strategy improves fungicide spray decisions; decreasing the number of sprays, and identifying the optimal time to spray to increase spray effectiveness.

Highlights

The rate of development and epidemiology of this disease are influenced by regional-scale, longer-term climate and localized, shorter-term weather uncertainty
It varies with growth stage and the genetics of a grape cultivar, making it difficult to develop efficient strategies for disease management
Most research on epidemiology and modeling of Powdery Mildew (PM) has been conducted for temperate climates

Summary

Introduction

Economic Importance of Grapes in North America. Grapevine growers across North America grow a wide range of grapes, mostly producing table grapes, raisins, and wines. Grapes and their derivative products represent a significant contribution to the economy of North America. As reported for 2015 in California, the primary U.S wine-grape growing region, grapes and their derivative products contributed $57.6 billion to the state’s economy and $114.1 billion to the U.S economy. In Canada, grapes are produced primarily in Ontario In 2015, the Canadian wine and grape industry contributed $9 billion to the Canadian national economy, with the province of Quebec contributing $1 billion [1]

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