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Analysis of Nonlinear Relationships in Dual Epidemics, and Its Application to the Management of Grapevine Downy and Powdery Mildews

August 2009 , Volume 99 , Number  8
Pages  930 - 942

Serge Savary, Lionel Delbac, Amélie Rochas, Guillaume Taisant, and Laetitia Willocquet

INRA, UMR Santé Végétale, IFR103, ISVV, 71 avenue E. Bourleaux, B.P. 81, 33883 Villenave d'Ornon cedex France.

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Accepted for publication 27 March 2009.

Dual epidemics are defined as epidemics developing on two or several plant organs in the course of a cropping season. Agricultural pathosystems where such epidemics develop are often very important, because the harvestable part is one of the organs affected. These epidemics also are often difficult to manage, because the linkage between epidemiological components occurring on different organs is poorly understood, and because prediction of the risk toward the harvestable organs is difficult. In the case of downy mildew (DM) and powdery mildew (PM) of grapevine, nonlinear modeling and logistic regression indicated nonlinearity in the foliage--cluster relationships. Nonlinear modeling enabled the parameterization of a transmission coefficient that numerically links the two components, leaves and clusters, in DM and PM epidemics. Logistic regression analysis yielded a series of probabilistic models that enabled predicting preset levels of cluster infection risks based on DM and PM severities on the foliage at successive crop stages. The usefulness of this framework for tactical decision-making for disease control is discussed.

Additional keywords:Erysiphe necator, injury threshold, odds ratio, Plasmopara viticola.

© 2009 The American Phytopathological Society