Gardeners who grow fruit crops need to be on the lookout. There is a new invasive intruder that may cause frustration to backyard fruit growers - the spotted wing drosophila.
The spotted wing drosophila is a relative of the vinegar fly. It originates from Asia. SWD was first discovered in commercial fruit crops in California around 2008. Given the efficiencies of our national commercial shipping services, the fly has quickly spread to many other areas of the U.S. It is just now beginning to emerge as a potential issue for home gardeners and commercial producers alike.
The spotted wing drosophila is a pest of soft-skinned fruits, such as raspberries, blackberries, blueberries, strawberries, grapes, plums, peaches, and more. Adults can be hard to detect and identify. At only 2-3 mm long, they are smaller than a house fly or fruit fly. Adult males can be identified (under magnification) by the two black dots present on their wings. Adult females have a saw-like ovipositor, or egg-laying appendage, on their rears.
SWD larvae feed on ripe berries and fruit of susceptible species. The larvae feed from within the fruit, often causing a sunken lesion to appear. In other cases, larvae will not be detected until after the fruit has been harvested and processed. Larvae are small, white, and worm-like.
Adult spotted wing drosophila females insert their eggs during fruit ripening using their ovipositor. The eggs soon hatch into larvae, which feed inside the fruit before maturing into the adult stage and re-infesting new fruit. As many as 15 generations of the fly have been detected in a single year by the USDA. Because the insect is a fairly new and emerging pest, control methods are still fluid. Simple traps can be made at home to help detect the presence of the fly. However, these traps will not help much in determining timing of controls.
Timely harvesting and sanitation practices can go a long way in helping control the severity of spotted wing drosophila infestations. Because they only infest ripe fruit, daily harvesting of ripened fruits will help limit the amount of hosts for females looking to lay eggs. If timely harvesting isn't possible during certain times, discarding of all overly-ripe fruit still on the plants will also help limit infestations.
If populations continue to increase, we may be forced to rely on chemical insecticides more frequently. There are several "conventional" insecticides labeled for SWD control. Most cases will require an application every seven days during fruit ripening and harvest. Spinosad, an organic insecticide derived from soil bacteria, can also be used to help control outbreaks.
SWD infestations have already been positively identified in our region this year. Please check your fruit crops for possible infestations. For more information on SWD identification, controls, and chemical recommendations, please contact the extension office.