The spotted wing drosophila (SWD), Drosophila suzukii (Matsumura), is a serious threat to the Florida blueberry industry. During the 2012 production season, SWD caused economic damage to blueberry growers in Florida that was estimated between 7-10 million dollars. The spotted wing drosophila is different from other vinegar fruit flies that infest overripe, rotting and decaying fruits. SWD cuts into ripening berries and lays its eggs, which develop into a maggot (larva) inside the berry. If one or more maggots are found in a container with berries the entire load could be rejected by a buyer. SWD is difficult to control after the eggs are laid because the larva develops inside the fruit and is totally protected from contact insecticides. It may be possible to kill the larva with systemic insecticides, but they usually have long PHI’s (post- harvest interval) and cannot be used during harvesting. The proper management approach is to prevent SWD from entering the blueberry planting.
There is a high potential (likelihood) for any blueberry planting to become infested with SWD. Even if your field is located in an isolated area, it is still likely to become infested with SWD because the fly has a wide host range (wild plants) and can readily be dispersed into blueberry plantings from neighboring fields. Despite not catching any SWD in several blueberry plantings prior to harvesting, high numbers of SWD were recorded in fields adjacent to blueberry plantings. Therefore, managing fields surrounding blueberry plantings is an important strategy that growers must adopt to effectively manage SWD population. Some common hosts include wild blackberry (Rubus sp.), wild grapes (Vitis sp.), red tip leaves (Photinia frazeria), and black night shade (Solanum nigrum). It may be a good idea to provide a buffer zone of approximately 30 feet between the brush and blueberry planting where wild hosts are removed. A second approach is to intercept the fly using border sprays (i.e., to treat an area of about 10-20 feet surrounding the blueberry planting). This treatment should be applied when five to 10 percent of the berries begin to turn blue.
Regardless of the strategy used for managing SWD, all management programs should include the use of monitoring traps baited with yeast-sugar water. Clear plastic cups with lids (with 8-10 holes in the upper part of the container) work as well as any commercial traps. These traps should be checked at least once per week for SWD. Once the field becomes infested there could be several generations before the harvest period is over, especially if infestation occurs with earlier ripening berries. Management of an infested field requires repeated applications of insecticides. It is important to rotate insecticides from the various classes and not to use the same class of insecticides for more than two consecutive applications during a production season. Our research has indicated that insecticides from the following classes, Synthetic Pyrethroid (Mustang, Danitol), Organophosphate (Malathion, Imidan), and Naturalytes (Delegate, Entrust) are effective products that can be used for managing SWD populations. A new product, Cyazypyr (Exirel), belonging to the class Anthranillic Diamides has just received registration in blueberries and is just as effective as the products listed above. Please contact Dr. Oscar Liburd at firstname.lastname@example.org if more information is needed on this topic.
OSCAR E. LIBURD, Professor of Fruit and Vegetable Entomology, University of Florida