Spotted Wing Drosophila
Spotted Wing Drosophila
The female SWD “stings”the skin of the healthy berries to lay 1 to 3 eggs. A female can oviposit on many fruit. Multiple larvae within a single fruit are quite possible, because many females might visit the same fruit to oviposit. Once fruit integrity is compromised by SWD activity, common vinegar flies also might oviposit in the damaged fruit.
What is SWD? Spotted wing drosophila (SWD), Drosophila suzukii, is a fruit fly first found in many California counties in 2008. It infests ripening cherries throughout the state and ripening raspberry, blackberry, blueberry, and strawberry crops, especially in coastal areas. It also has been observed occasionally attacking other soft-flesh fruit such as plums, plumcots, nectarines, and figs when conditions are right.
How to manage SWD? Spotted wing drosophila flies and their damage often are not noticed in backyard fruit crops until fruit is being harvested. Sprays at this time will not protect the crop, because maggots already are in the fruit (see Chemical Control below).
If a small percentage of fruit is infested, you can salvage some of the crop by harvesting the crop immediately and sorting and removing fruit with stings on the surface. Place infested fruit in a sturdy, sealed plastic bag and dispose of it in the trash. A combination of preventive and cultural practices, discussed below in Cultural Control, might be useful for reducing problems on fruit trees and berries.
Cultural control: Sanitation, netting and early harvest can significantly reduce the problem with SWD.
Sanitation: Eliminating any fruit that has fallen on the ground and any infested fruit remaining on plants in the garden can reduce populations of flies that might infest next year’s crops or later-ripening varieties. Infested fruit can be placed in a durable plastic bag, sealed, and placed in the trash. Composting or burying is not a reliable way to destroy eggs and larvae in fruit. Solarizing fruit under clear plastic in the sunshine has been quite successful in killing flies in fruit in preliminary studies performed in Oregon.
Netting: Fine netting over whole plants or canes can be useful to keep flies from attacking fruit on blueberries and other small fruit and possibly on branches on small cherry trees. However the netting must be applied before fruit begins to ripen so that flies will not be caught inside the net. Netting must be secured so flies cannot enter, and the mesh size should be very small, such as 0.98 mm mesh used for screening out no-see-um flies.
Early Harvest: Early harvest of fruit can be important in reducing exposure of fruit to the pest. Begin harvest as early as you can and continue to remove fruit as soon as they ripen.
Trapping: Trapping has not been shown to effectively reduce populations of SWD in backyard trees but is important for monitoring SWD activity.
Biological Control: researchers are looking for suitable predators, parasitoids, pathogens and other beneficial organisms that might help suppress SWD populations.
Chemical Control: The insecticide Spinosad (e.g., Monterey Garden Insect Spray) is effective and has the least negative environmental effects of currently available products. Some Spinosad products are sold to be applied with a hose-end sprayer, but a compressed-air sprayer will give more reliable coverage.
For more information on SWD visit UC IPM Online.