Evaluation of a CAA-based downy mildew management strategy in a vineyard with CAA resistance

The effectiveness of two treatment strategies with or without the CAA fungicide mandipropamid against the grapevine downy mildew agent Plasmopara viticola has been evaluated during three grapevine growing seasons in a vineyard with a high disease pressure. CAAs resistance was reported in this location before the study. Compared to the untreated plot (disease severity higher than 65% on leaves and 95% on bunches), both the CAA and NO-CAA strategies adequately and analogously protected the plants from heavy infections, avoiding yield losses (severity <15% on leaves and <4% on bunches). Biological and molecular assays on P. viticola populations collected from the untreated and treated plots showed that resistance in the field is mainly associated with G1105V mutation in the target CesA3 gene and that resistance frequency did not increase in the populations when applying the CAA mandipropamid following an anti-resistance strategy.