LAUSR

BACKGROUND Oxathiapiprolin is a piperidinyl thiazole isoxazoline fungicide discovered by DuPont and commercialized by Corteva Agriscience. It acts by inhibiting a novel fungal target, an oxysterol binding protein (OSBP), and is intrinsically highly active against oomycetes including grape downy mildew (Plasmopara viticola) and potato late blight (Phytophthora infestans). Because the fungicide acts at a single site there is a need to determine the risk of resistance development. RESULTS Oxathiapiprolin controlled European P. viticola and P. infestans isolates at very low concentrations with EC50 values ranging from 0.001 to 0.0264 mg L-1 and 0.001 to 0.03 mg L-1 , respectively. Laboratory mutagenesis studies performed with Phytophthora capsici using UV irradiation generated mutants with reduced sensitivity to oxathiapiprolin. All resistant mutants had a base pair change in the OSBP gene that resulted in an amino acid change. Most common substitutions were S768Y, G770V, G839W and L863W. Isolates of P. viticola and P. infestans with reduced sensitive were also detected in field trial sites where oxathiapiprolin had been applied repeatedly each season over several consecutive years. CONCLUSIONS The risk of oxathiapiprolin resistance development in P. viticola and P. infestans is medium to high and strict resistance management measures are required. Over-exposure of target populations to single-site fungicides during product development should be avoided. This article is protected by copyright. All rights reserved.