Adult monitoring improves control of the flavescence dorée leafhopperScaphoideus titanus in Gironde (France) while using less pesticide!

Abstract: The flavescence dorée is caused by a phytoplasme spread by the leafhopper Scaphoideustitanus and is present in the south of France. Leafhopper control is based on up to 3 obligatoryinsecticide sprayings (T1; T2; T3) using neurotoxic insecticide compounds over large areas(Imposed Sprayed Area = ISA). Spraying dates are defined according to the observation of the firstlarvae (T0) at T1= T0+4 weeks, T2 = T0+6 weeks (T1 and T2 aim the larvae) and T3 = T0+10weeks (aiming at adults). Such schedules and area definition are very efficient but lack scientificbasis on insect dynamics and migration and encounter opposition from farmers.Over the last 5 years progress was made to reduce pesticide use while maintaining sufficientvector control. A project was launched in the Saint Emilion region after two plots were foundcontaminated in 2006. 13000ha of vineyards entered the ISA. Farmers and regional Plant protectionservice organised into a small association to test a more ‘integrated’ approach for vector control.Spraying zones were limited to a buffer zone of 2 km around the contaminated plots. Farmersbetween 500m and 2 km were allowed to reduce sprayings to only 1 single application at T0 + 5,while adult trapping was used to monitor overall results. Traps were yellow delta traps (PiègeTri-nglué) that are highly efficient. In most of this zone a single insecticide spray reduced trapcatches to almost nonexistent, considered as a proof of sufficient control of the vector. In someareas trap catches were considered too important (>3 adults on a single trap in a single week) and asecond spraying (T3) was imposed. This was probably due to some farmers either not spraying atall or organic farmers that only were allowed Rotenone, that is rather inefficient. This approach wasrepeated in 2008.Total cost of trapping and monitoring of larvae (traps, technicians, monitoring) is around 3 to 4Euros per ha. These costs were largely compensated by the reduction in spraying (64 and 72 percentreduction in 2007 and 2008 compared to the traditional approach). Moreover, the combination ofreduced spraying and vector monitoring seemed well accepted by the farmers.In addition all plots were monitored for plants showing symptoms of phytoplasm, around 1200samples were analyzed first year. Over 80% of the samples appeared to be ‘Bois Noir’ phytoplasmbut some Flavescence Dorée samples were found in both 2007 (2 samples) and 2008 (6 samples).Scouting and analysis costs were around 25 Euro per ha.In other areas where spraying frequency was reduced simultaneously but without vectormonitoring, a strong increase in FD symptoms was observed, together with high insect populations.This probably reveals that many farmers do not apply the single imposed spraying. The trappingseems a useful tool both to show efficient vector control and to incite farmers to respect theminimal spraying frequency.