–Jim Jasinski (jasinski.4@osu.edu), IPM Program; Celeste Welty (welty.1@osu.edu), Dept. of Entomology
Spotted wing Drosophila (SWD) is a serious pest of raspberries, blackberries, blueberries, strawberries, grapes, and peaches. For the past five years, we have established a statewide monitoring network in 15-20 Ohio counties to look for this pest on grower’s farms in an effort to help them manage it better. With few exceptions, in every county where we have placed traps, we have found SWD. This network is typically established in the first week of June and runs through September, and consists of weekly trap checks and reporting.
Over the years we have gained some knowledge about the overwintering habits of this pest, which appear to be near wooded areas. This year we set out baited Scentry traps early at a few small fruit fields around the state to see if SWD are present in those locations. In Franklin Country, one trap was in place in a small raspberry patch for the entire winter, and four additional traps were placed near the boundary between a wooded fencerow and the raspberries on May 11th. Likewise, traps were placed in the boundary between the woods and berry fields in Greene and Clinton Counties on May 10th. In Wayne County, traps were also placed near a strawberry field in mid-May. We have detected SWD adults at all four of these locations within the past week. In Franklin County, the traps in the berry patch had no SWD, but one trap in the distant treeline did have one male SWD on May 25th. Traps at Greene, Clinton, and Wayne locations found SWD adults on May 23rd. These catches are 3-4 weeks earlier than we have detected them in past seasons. The earlier finds are interesting but not surprising, because we were looking for these pests earlier in the season at a location where they are likely to overwinter, in combination with a mild winter in which high survival was likely.
SWD adult imaged through stereo scope. This is a male, note spots on wings.
SWD Scentry trap with Scentry lure (inside) and 25% apple cider vinegar drowning solution set in a raspberry field.
What does finding SWD this early in the season mean for growers? We are still learning about this pest and how to interpret the nuances of early season detection and its effect on early season management. Strictly speaking, the threshold for this pest is one adult fly detected in the fruit planting, so if there is any ripe or ripening fruit on a farm, we recommend starting an insecticide treatment on a seven-day schedule through harvest. If growers cannot treat due to picking or harvesting considerations, we strongly recommend they conduct salt water tests on berries collected from several locations around their susceptible fields to verify no SWD larvae are found in the berries. If larvae are found, treatment should begin immediately through harvest.
All growers of these susceptible crops are encouraged to use a trap to detect the adult flies, and test ripening fruit for presence of larvae using a simple salt water test.
A factsheet on how to conduct a saltwater test can be found here: http://u.osu.edu/pestmanagement/files/2017/04/SWD-salttesthandout-updated-pnd335.pdf.
Insecticide options available to growers along with pre -harvest intervals, are shown on page 2 of a factsheet: https://u.osu.edu/pestmanagement/files/2017/04/SWD_Ohio_handoutV15-1fd4zp6.pdf