The suzuki fruit fly, a cherry loving exotic species that causes a lot of damage to Dutch fruit crops, was kept reasonably under control this year says Herman Helsen. The Wageningen University researcher examined the development of the invasive fly and shared his findings during the NFO Knowledge day on Friday, November 20th, "The decrease in attacks on cherries was, in part, due to the use of the plant protection products Tracer and Exirel. These products were used when the cherry ripened and egg laying was observed; and it was a success. Untreated cherries seemed to be able to resist the fly at first, but half way through July we saw noticeable deterioration. When treatment was no longer possible in July, we stopped harvesting."
Other fruits were also not completely free of the suzuki fly, "The raspberry crop has strict hygiene and is plucked daily, with direct disposal of damaged fruit. They are also treated with plant protection products (pesticides). It is not entirely clear how the different treatments contributed to the relatively low attack." It was a bit more difficult with the blackberries, "Due to the longer ripening period, intensive treatment is often needed and in some cases they had to stop harvesting." There were problems with red berries in 2014. According to Herman, in 2015 there was local damage, "This was really only in moist areas and near places where cherries were also being grown."
"An important question is if the adult flies can survive over the winter," says Herman. To answer this question the research team installed ten meters of grass and black strip nets with fruit fly traps underneath in February. Traps were also placed outside the nets, "We never found a fruit fly under the net," says Herman. "In mid-March we found fruit flies immediately next to the covered areas. We are dealing with flies that do not stay through winter but appear in early spring."
Six generations in 2015
Herman concludes that cherries play a very crucial role with the first generation, "We have never been able to observe reproduction on winter fruits in early spring, the same goes for research in Switzerland and Italy. In Southern Germany they have found reproduction on ivy and mistletoe. Mass reproduction does not occur until the first cherries start to ripen in the beginning of June. The flies then lay their eggs and in the last week of June these flies have reached maturity. Ultimately, we counted a total of six generations of fruit fly in 2015."
Preventative measures, like placing nets with a maximum mesh size of 1 square millimeter, has proven effective in curbing fruit fly infestation. In the cherry orchard used for the research in Randwijk, placing nets had good results, "In the cherry orchard in Randwijk the tress were covered with nets from Voehn (0.8x0.8mm) and Rovero (0.74x0.95mm). When the first cherries started ripening in June these nets were closed. The cherries were additionally treated with pesticides. We then followed up by placing traps both in and on the nets. A fruit fly was never caught inside the mesh. Outside the nets is where we caught most of them." In short, with the right timing and right measures the suzuki fly can be managed.