Controlling Scaphoideus titanus with kaolin? Summary of four years of field trials in Switzerland

Flavescence dorée is a quarantine phytoplasma-borne disease transmitted primarily by the leafhopper Scaphoideus titanus. When S. titanus and Flavescence dorée are present in the same vineyard, the vector has to be controlled mandatory with insecticides to limit the transmission of the disease to healthy grapevines. Natural pyrethrins are currently the only registered insecticide to control this vector in Swiss commercial vineyards. To find alternative products against this insect, we tested the effectiveness of kaolin, a white inert aluminosilicate mineral, in 11 independent field trials over four consecutive years from 2018 to 2021. Using kaolin at rates between 20 and 40 kg/ha applied two to three times at the beginning of hatching resulted in an average reduction in leafhopper densities of 36.8 %, with efficacy values ranging from 0 to 88.9 % for the 18 different interventions. Overall, the efficacy of the different kaolin dosages and application strategies did not equal those commonly recorded for natural pyrethrins, which showed a mean efficacy of 74.8 % in the six independent field trials and single reduction values ranging from 41.3 to 97.4 %. Given these highly variable efficacy levels of kaolin, we conclude that the use of kaolin to control S. titanus does not provide an efficient alternative to natural pyrethrins in compulsory control areas of Flavescence dorée in Swiss vineyards.