Mary Concklin, Fruit IPM Extension Educator
Updated spring 2013
The Spotted Wing Drosophila (SWD), Drosophila suzukii, is an invasive vinegar/fruit fly that arrived in Connecticut with a vengeance in the late summer of 2011 forcing the end of fall raspberry harvest across the state. This new pest is different from all other vinegar or fruit flies in that it lays its eggs in soft, thinned skin fruit that is just beginning to color. Other common fruit flies lay eggs in over-ripe or decomposing fruit. Fruit considered to be at highest risk are raspberries (particularly fall varieties), blackberries, blueberries (particularly late varieties), day-neutral strawberries, and, at least on the west coast, sweet cherries. Those considered to be at moderate risk are peaches, grapes, and possibly June strawberries.
The SWD eggs hatch in 1 to 3 days and the larvae, also referred to as maggots, feed in the fruit for about a week, pupate and then emerge as adults anywhere from 4 to 15 days later. This short life cycle from egg to adult means we will have to deal with many generations in a year.
Photo by G. Arakelian, Oregon Dept. of Agriculture
In addition to maggots inside the fruit, another problem associated with the SWD is the introduction of bacteria and fungi into the fruit when they lay eggs, leading to fruit rot.
When will we begin to see the SWD in large numbers? We aren’t sure. Will there be a significant population during strawberry harvest to deal with? Again, we aren’t sure. We suspect the SWD will be able to over-winter in CT because it has over-wintered in colder states such as Michigan. We are learning a great deal about the new pest and its survival in the northeast. Dr. Rich Cowles of the CT Agricultural Experiment Station, and other researchers in the US, received Urgent IPM Grants for SWD and have been looking at the life cycle, its feeding habits and preferences and how to use those to our advantage in managing this pest. As soon as new information is available, we will get it out to you via email. If you are not on the fruit email list and would like to be added, send an email to me at firstname.lastname@example.org.
Trapping is the first step in managing this pest, although at this point traps are important for letting you know that SWD are there, not for complete control. Traps are easy to make. A report from Oregon researchers indicated the commercial traps were not as effective as using deli or other plastic containers for catching SWD. Washington State has a factsheet on how to make a trap using vinegar and yellow sticky traps.
In 2011 & 2012, baits were made of apple cider vinegar (be sure to use REAL apple cider vinegar, not flavored – check the label), and changed weekly. Add a drop of unscented soap to the vinegar. This will help reduce surface tension making it easier to trap the flies. As you catch more flies you may need to change the bait more often and/or switch to a larger container. Hanging a yellow sticky card inside the container may make it easier to identify the male SWD. Work conducted in 2012 and early 2013, indicated a bait that appears to be more attractive to SWD contains yeast, sugar, water and whole wheat bread.
Other fruit flies will also be caught in the traps, so don’t assume everything is a SWD. Don’t worry about identifying the females. It is the spot on the wings (location and size) of the males that distinguishes them from others. Penn State University has an excellent factsheet with pictures of the male SWD and other look-alikes.
Trap catches this winter (2012) were non-existent after late December. The first trap catch of this season (2012) was in early April of a single male SWD in southern CT. Therefore it would be wise to err on the early side rather than later and begin monitoring now. It would also be prudent to inform any homeowners in your area who have berries and soft skinned tree fruit in their yards about the trapping. Everyone working together will make managing this pest a bit easier.
Sanitation is another key component of SWD management, although not as easy to accomplish in pick-your-own operations. Where possible, try to remove infected fruit, over ripe fruit (that includes tree fruit that are over-ripe and soft as they are potential breeding sites) and infected fruit that has dropped. Do not compost – destroy it. Stay on top of harvest by keeping bushes picked of ripe fruit.
Remove alternate hosts such as wild brambles, Autumn olive and wild grapes.
- Biological Control
Research is underway looking at potential biological control agents including parasitoids. To date, none have been found to provide satisfactory control of SWD populations. But stay tuned.
- Cultural Control
Japan has experimented with covering blueberries with 0.98 mm grid size mesh (extremely small!) and found it provided 100% control. That is an option that needs further investigation and may be practical on a small scale or for high tunnel production.
- Chemical management
There is no reason to spray as soon as you begin to catch the SWD in traps. They won’t be laying eggs in your crops until the fruit are turning color. Research has found that spraying earlier did not lower the population.
Once fruit begins to turn and SWD are detected in traps, chemical control will be essential and is aimed at the adults. Chemical choices include many inorganic and organic materials. Refer to the New England Small Fruit Pest Management Guide for an up-to-date listing of labeled materials.
The information in this document is for educational purposes only. The recommendations contained are based on the best available knowledge at the time of publication. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension System does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available. The University of Connecticut, Cooperative Extension System, College of Agriculture and Natural Resources is an equal opportunity program provider and employer.