Predicting regional-scale spread of ascospores of Didymella pinodes causing ascochyta blight disease on field pea

Ascochyta blight is the most destructive foliar pathogen of field peas. The amount of yield loss resulting from the disease in Australia is mainly driven by primary infection from wind-borne ascospores of Didymella pinodes. In this study, a model was developed to predict the spread of ascospores from the ascochyta blight infected field pea stubble of previous season’s crops. The model was adapted from a previously developed spatiotemporal model and calibrated with field experimental data consisting of release events of ascospores of D. pinodes from known source for 21 consecutive weeks, under natural environmental conditions, in a 400 m by 400 m area. The model was then applied in a 30.9 km by 36.8 km area in a major field pea growing region of Western Australia to show the magnitude and spatial diversity of the dispersal of ascospores, generated in previous season’s field pea stubble, could differ between growing seasons. This simulation was only tested subjectively. It is concluded that a properly validated simulation of this type has potential for understanding the value of physical separation of the current season field pea crop from previous season’s stubble, visualising the scale and diversity of ascospore dispersal as an educational tool for growers and consultants, and deriving the “magic figure” of the intensity of field pea area that could result in the presence of ascospores everywhere in a region.