Advice from the Help Desk of the
UC Master Gardener Program of Contra Costa
Female spotted wing drososphila
Client's Request: I have not gotten a good crop of cherries in the past several years due to that relatively new pest, the spotted wing drosophila, that leaves its maggots in my fruit. Is there any new information on how to manage this pest in the home garden?
Help Desk Response: The spotted wing drosophila (Drosophila suzukii) is a relatively new pest of cherries and other soft fleshy fruits (strawberries, raspberries, blackberries, blueberries, etc). Unlike other vinegar flies that attack rotting or fermenting fruit, the spotted wing attacks maturing fruit. The name spotted wing drosophila comes from the single black spot at the tip of each wing of the male adult. Don't think though that you will be able to identify this fly by those markings without magnification because these adults are small, really small. The female is able to penetrate the skin of the fruit to lay her eggs and this act creates a small depression (“sting”) on the fruit surface. The eggs hatch and the maggots develop and feed inside the fruit, causing the flesh of the fruit to turn brown and soft.
Male spotted wing drososphila
Because this pest is relatively new to California, there has been limited research on treatments to manage it, especially for home gardeners. The organophosphate insecticide malathion is known to kill spotted wing drosophila, but only if the tree can be completely covered with the spray. Complete coverage is often difficult, especially with larger backyard trees, because of limitations of available equipment. Application should be made as soon as the fruit just begins to turn from yellow to pink. This should be about 2 to 3 weeks before cherry or berry harvest as the spray must kill adults before they lay eggs. Malathion is very toxic to bees and natural enemies of other pests in the garden, so care must be taken to keep the application on the tree and avoid drift and runoff. Improper application can also result in injury to the tree. Because of the potential negative impact of malathion in the garden, use it only where you are certain you will have a spotted wing infestation, either because you had a problem last year or from trapping and positively identifying insects this season as spotted wing. (More on the use of malathion can be found at http://www.ipm.ucdavis.edu/TOOLS/PNAI/pnaishow.php?id=46)
An alternative to malathion with fewer negative environmental effects would be spinosad (e.g., Monterey Garden Insect Spray and see http://www.ipm.ucdavis.edu/TOOLS/PNAI/pnaishow.php?id=65); hEgg-laying scar or "sting" in cherry
owever, spinosad is not believed to be as effective against the fruit fly adults as malathion. To get satisfactory control two sprays may be required; the first applied as the fruit just begins to turn pink and the second applied 7 to 10 days later. As with malathion, all foliage and fruit on the tree must be covered with the spray. Partial coverage will not be effective. A compressed air sprayer will give more reliable coverage than a hose end sprayer.
Since spotted wing drosophila attacks ripening fruit it is often not noticed in home garden situations until the fruit is being harvested. Sprays at this time will not protect the crop because maggots are already in the fruit. If only some of the fruit are infested, you can salvage some of the crop by harvesting immediately and sorting the fruit, removing any with “stings” on the surface. It is recommended that all infested fruit be removed from the tree and picked up from the ground. It should then be placed in a sealed plastic bag and disposed of in the trash or buried. Do not put the infested fruit in your compost pile as it may not get hot enough to destroy the eggs and larvae still in the fruit.
For even more information on controlling the spotted wing drosophila, please go to this University of California website http://ipm.ucdavis.edu/EXOTIC/drosophila.html
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This blog was originally written by Emma Connery, Retired Master Gardener Program Coordinator, for publication in the Contra Costa Times April 2, 2011. Slight changes have been made to the original for this blog and are the full responsibility of the blog editor.
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Help Desk of the UC Master Gardener Program of Contra Costa County
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Posted on
Monday, March 28, 2016 at
1:03 AM
This a brief summary of the information presented at yesterday’s meeting in Stockton about the cherry vinegar fly, now known as the spotted wing drosophila (SWD), Drosophila suzukii. The purpose of the meeting was to update researchers, growers and industry personnel on the status of this pest.
Spotted wing drosophila has now been found in cherries, raspberries, blackberries, blueberries, and strawberries in California. It has been found in many (I think the number was 21) counties across California, as well as several other states. However, in the case of detections from other states, it has not yet been determined whether the detections come from fruit grown in those states or simply were fruit from infested areas of California incidentally brought back into California.
Of the 3000 species of Drosophila commonly known as vinegar flies only two have been found to be harmful to crops, of which the spotted wing drosophila is one. The female has a serrated ovipositor, meaning she can penetrate the skin of most thin skinned fruit. In the lab it takes from 2-3 minutes to oviposit, and this oviposition is not necessarily successful each time. Nevertheless, in an experiment done by Artyom Kopp from UC Davis, three females put in a test tube with a Thompson seedless grape had several dozen eggs laid overnight. A female will lay 2-3 eggs per fruit, and will lay around 350 eggs in her lifetime. The life cycle in the laboratory, from egg to egg laying female, is 12 to 15 days at 65o F. The egg and larvae develop inside of the fruit, and while experts at the meeting said that pupation takes place inside of the fruit also, I have taken many samples of strawberry and raspberry and they are always exiting to pupate.
It is thought that SWD will have ten generations per year, and probably 3 generations in one crop of cherries. Thus, the population growth potential of this pest is tremendous. They are most active at 68o F and activity becomes reduced at temperatures above 86o F. Above 86o F, males become sterile. Eggs, larvae and adults (probably pupae are not far behind) die at temperatures below freezing, but this does not necessarily mean a whole population will be eradicated at lower temperatures, since D. suzukii is firmly established on the island of Hokkaido in Japan, where winters are quite cold. Additionally, vinegar flies in general are very sensitive to dessication, and will die within 24 hours in the absence of water.
On the regulatory side, we were informed that neither the CDFA nor the USDA are recommending any regulatory action (such as a quarantine) at this time. On a conference call regarding SWD with USDA and the National Plant Board, no other states made any commitment to conduct a survey for this fly. While the state of Oregon may have some concerns with this pest, they have to prove an absence of it before any action can be taken.
Photo Courtesy Ed Show
Spotted wing drosophila adults on raspberry.
Posted on
Thursday, July 9, 2009 at
9:40 AM