A model for the development of Erysiphe necator chasmothecia in vineyards

A temperature-driven, mechanistic model predicting the development of Erysiphe necator chasmothecia in vineyards\r\nwas developed and validated in 38 vineyards in the Po Valley (northern Italy), Baden-W€urttemberg (Germany), and\r\nSouth Australia between 2005 and 2011. The model, which begins operating when the first ascocarp initials are\r\nformed, predicts on a daily basis the proportions of chasmothecia at the yellow, brown and black maturity stage. The\r\ninitialization date was estimated with an iterative procedure that minimized the residuals of predicted versus observed\r\nvalues. In all vineyards, a drop to more favourable temperatures for ascocarp production over 2–4 days in the week or\r\nin the 2 weeks before the model initialization date probably triggered chasmothecia production. Model predictions provided\r\na good fit of observed data (coefficients of determination, model accuracy, efficacy and efficiency were all ≥0 90),\r\nwith some overestimation. When predicted production of black chasmothecia (on leaves) was compared with observed\r\ndispersal of chasmothecia from vines, lack of splashing rain was probably the main cause of overestimation. When\r\nobserved numbers of yellow, brown or black chasmothecia on leaves were compared with model predictions, removal\r\nof the developing chasmothecia by rainfall was probably the main cause of overestimation. Inclusion of the effect of\r\nrainfall on the removal of immature and mature chasmothecia from the powdery mildew colonies could improve the\r\nmodel. The model could be used to time the application of fungicides or biocontrol agents for reducing ascocarp formation\r\nand reducing primary inoculum in the following season.