Spotted Wing Drosophila and Small Fruit Production

Spotted wing Drosophila (SWD) is a serious invasive pest of soft-skinned fruits. SWD was first detected in Kentucky in 2012, by midsummer of 2014 SWD could be found throughout Kentucky at high levels. This fruit fly lays its eggs in soft-skinned fruits as they soften before harvest; this new pest not only causes issues for the commercial grower but the home gardener as well. SWD attacks many different soft-skin fruiting crops, but the most serious damage in 2013 was to raspberries, blackberries, blueberries, and grapes. It also breeds in fruit of native wild plants like pokeweed, mulberries, wild blackberries, and nightshade. The female SWD uses her serrated egg layer to cut into the skin of otherwise intact soft-skinned fruits to deposit her eggs. Each female deposits 7 to 16 eggs a day and up to 300 eggs during its lifetime. Eggs hatch in 2 to 72 hours, resulting in small larvae in harvested fruit. SWD will overwinter in Kentucky as it survives in states to our north and parts of Canada. 

Here are some great tips for checking fruit and management of SWD from UK Extension Entomologist Ric Bessin:

Checking Fruit: When harvesting take the time to thoroughly look over each berry. Externally berries may look unifested but larvae may still be inside. If a berry is very soft, collapsing on itself, or is watery near the cap of the fruit, SWD larvae are most likely present. These berries should be discarded away from the field, and preferably bagged for disposal. We are not aware of any known risk to human health by ingesting SWD eggs and larvae.

Management: Refrigeration- Berries that have no visible damaged should be placed directly in the refrigerator. Placing the berries in the refrigerator will stop the development of the SWD if they are present, both hatched and unhatched. Freezing berries will kill SWD and holding berries at 34F for 72 hrs will kill most of the eggs and larger larvae.

Netting-  Mechanical control maybe an option for homeowners, as with many of the small fruit crops we often use netting to keep the birds from eating the berries. For the SWD the same concept applies except the netting must be a fine mesh, with opening of less than 1 mm. ProTekNet is a brand of netting that provides netting small enough (less than a 1mm square opening) that can exclude SWD, but spun bond row covers should work as well. Netting should be placed over the planting when the earliest berries begin to turn color prior to harvest. Netting may interfere with pollination of later raspberry flowers, but this maybe a sacrifice to save the rest of the crop. The netting must be secured along the ground to prevent any openings for SWD to enter. On larger plantings a structure might be installed to help support the netting and allow a person to pick underneath the netting. The netting will have to remain over the crop until harvest is finished.

Sanitation- It is also important to remove any damaged fruit from the field, as these fruits may contain SWD eggs and larvae. Overripe, damaged, or rotting fruit should be collected, placed in clear bags, and left in the sun.  Burial of infested fruit is ineffective as the larvae can emerge from depths of one foot or more.

If you suspect you have a spotted wing drosophila problem, or would like more information on SWD, please contact the McLean County Cooperative Extension Office at (270)273-3690.  Educational programs of the Cooperative Extension Service serve all people regardless of race, color, sex, religion, disability or national origin.