SWD larva feeding on a raspberry
Spotted wing drosophila (SWD) is a fruit fly that over the past five years has become a significant pest of fruit crops such as strawberry, raspberry, blackberry, blueberry, grape, peach and plum. This insect causes damage when its larva – tiny white worms – feed on and within ripening fruit.
Beginning in early June throughout Ohio a number of county OSU Extension offices regularly monitor for the presence of SWD on several fruit farms. By the third week of June this year SWD had been detected in Clinton, Franklin, Greene, and Wayne Counties. Similarly, small fruit growers who have fruit that is ripe or near ripening should also be monitoring for this pest. If growers are not able to trap for SWD, a salt water test should be conducted on healthy berries every few days to determine if they have an infestation. If adults or larvae of this pest are detected, the recommendation is to begin a weekly insecticide spray program until harvest is complete.
The SWD is an economical as well as fruit quality threat to fruit producers and reduces the marketability of fruit. Unlike the common fruit or vinegar flies that are a pest of over-ripe fruit, the SWD is able to damage fruit as it starts to ripen. Each female fly can lay between 300 to 350 eggs. Under optimum conditions, the lifecycle from egg to adult can be completed in eight to ten days and there are multiple generations per year. Without preventative treatment, numbers can quickly build to high levels, making that fruit generally un-marketable.
At this point, the only reliable method for a high degree of control is the use of chemical insecticides applied on a regular and consistent spray schedule. Thorough spray coverage is essential for good control, from the top to the bottom of the plant and spray needs to penetrate into the plant canopy. In addition to the use of insecticides, damage by SWD can be minimized by storing fruit at cold temperatures as soon after picking as possible. Research indicates that fruit quality is maintained and cold storage can produce mortality of both mature larvae as well as eggs. Sanitation also plays a role in control and reducing the number of SWD.
Home gardeners and commercial fruit producers alike are encouraged to rotate between chemical classes to reduce the possibility of chemical resistance developing in the SWD population. More information about the SWD and its lifecycle, along with a chart of labeled and approved insecticides used to control the pest and timing of insecticide applications can be found at http://u.osu.edu/pestmanagement/pests/swd/
Below is a brief video explaining the Salt Water Test for SWD Larvae in Fruit.
– Stan Smith, PA, OSU Extension, Fairfield County