Sensitivity of Uncinula necator isolates to quinoxyfen: baseline studies, validation of baseline method, and targeted sensitivity monitoring after several years of commercial use

摘要

Prior to the launch of quinoxyfen against powdery mildew in vines, a bioassay was developed to assess the sensitivity of monoconidial strains of Uncinula necator to this compound. The sensitivity profile showed a wide distribution of EC50 values ranging from < 0.03 to 2.6 mg litre"1. Post launch, the baseline distribution for quinoxyfen was confirmed and methods were validated (1999-2000). The bioassay was adapted to a second laboratory and differences due to use of different facilities and samplingmethods were assessed. Some variability in the sensitivity distribution (mean EC50 values) was observed between samples. However, all isolates fell within the baseline range. Evaluation of sales data and analysis of farmer use surveys have shown that insome regions quinoxyfen sustains a very high market share during a period of intense disease pressure. Since 2002, sensitivity monitoring has been targeted to vineyards in these regions. Some adapted isolates are now present. However, there is no evidence of disruptive resistance in the field. In order to strengthen resistance management recommendations, quinoxyfen is limited to no more than two consecutive applications in these regions. An innovative solution is proposed for areas of intense selectionpressure and registration for a pre-pack mixture of quinoxyfen + myclobutanil has been applied for.