Minimising insecticides for control of spotted wing drosophila
Drosophila suzukii is a major pest of soft fruits, laying eggs in fruit before it is harvested. Control remains dependent on routine applications of insecticides. In semi-field experiments we tested the possibility of reducing the amount of insecticide needed to control D. suzukii by combining lower rates, volumes and area of application, in combination with phagostimulant baits in comparison to full field rates of the insecticides and an untreated control. The baits were (1) Combi-protec - a proprietary mixture of plant extract, proteins, and sugars (2) a suspension of the yeast Hanseniaspora uvarum and (3) molasses. Low insecticide rates were 4% of the full rates and were attained by diluting the insecticide concentration in the spray and reducing the sprayed volume. The low rate was applied as a coarse quality spray in a swath across the middle of the strawberry or raspberry crop. The full rate was applied as fine droplets to the entire crop canopy. In strawberry the Combi-protec with a low rate of cyantraniliprole resulted in the same level of control of D. suzukii as the full rate. Combi-protec was a more effective bait than the H. uvarum suspension. In raspberry, the average spray deposit coverage on the crop was approximately eight-times higher with the full rate application compared with the low rate application. However, low rates of cyantraniliprole and spinosad with Combi-protec or molasses baits were equally effective in D. suzukii control compared to the full rates of insecticides. In raspberry, the cost of the four full rate sprays of insecticides was £74 ha-1 or £314 ha-1 more than the four low rate insecticide sprays with Combi-protec or molasses respectively. The low rates of application resulted in fruit insecticide residues being less than 11% of those from raspberries sprayed with the full rates.