Maggots in My Cherries Again This Year?

Advice from the Help Desk of the
UC Master Gardener Program of Contra Costa

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.

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); h

Egg-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.

Larva in 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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Come to the UC MGCC Program's Great Tomato Plant Sale
Walnut Creek 4/2&9, Richmond 4/9, and Antioch 4/16
Click for locations and plant lists!
Dozens of heirloom tomatoes & vegetables chosen especially for Contra Costa

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Note: The  UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions.  Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA  94523. We can also be reached via telephone:  (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog  (//ucanr.edu/blogs/CCMGBlog/).