Estimating the incidence of Septoria leaf blotch in wheat crops from in-season field measurements

Abstract

Septoria leaf blotch is a widespread disease caused by the fungus Zymoseptoria tritici (formely known as Mycosphaerella graminicola). It causes yield losses in winter wheat crops (Triticum aestivum L.) in many European countries. In this study, we aimed to develop statistical models for estimating regional and site-specific incidence of Septoria leaf blotch from in-season field measurements. Four generalised linear models and four generalised linear mixed-effect models were fitted to six years of data collected from a major wheat-producing area of France, using frequentist and Bayesian methods. We compared the abilities of these models to predict S. tritici incidence over different time scales. We found that the best models were those that included site-year effects and disease risk ratings based on sowing dates and cultivar resistance levels. These models can be used to estimate the dynamics of disease incidence from observations collected in regional surveys and, as such, could help regional extension services evaluate current disease incidence at the regional scale. The proposed models could also be adjusted to make use of site-specific in-season field measurements for the estimation of site-specific disease incidence. With the current survey design, site-specific estimates are more accurate than regional estimates after mid-May. Such estimates could be used to help farmers adapt their control strategies locally during the growing season.