Thursday, May 13, 2010

Cherry Maggots Come to Town

"Cherry Maggots Come To Town" would be a great name for an indie band. Unfortunately, this is one insect you don't want performing in your yard. The spotted wing drosophila (SWD), is responsible for the little worms that backyard gardeners are starting to find in their cherries, and to a lesser extent in raspberries, strawberries and blueberries. First spotted in Santa Cruz County in 2008, this pest is now throughout the West Coast, and has been spotted recently in traps in Sacramento County. 

According to Sacramento County Farm Advisor Chuck Ingels, the adult SWD is small (2-3 mm), resembling a gnat that might be found on that old piece of fruit on your kitchen counter. This one, though, has a sharp ovipositor (sort of a needle-like, egg-laying device) that penetrates ripening fruit...such as your backyard cherries, that are just a few weeks away from harvest right now.

 Adult male spotted wing drosophila, Drosophila suzukii, (2-3 mm long) has a dark spot on each wing tip.
Photo by Martin Hauser.

Adult female spotted wing drosophila, Drosophila suzukii (2-3 mm long).
Photo by Martin Hauser.

This pest might easily be confused with a vinegar fly or the western cherry fly. Western cherry fruit fly adults are much larger (5 mm) than the spotted wing drosophila adults and have a dark banding pattern on their wings. The western cherry fruit fly, which is a quarantine pest, occurs in Washington and other states but has not established in California. 

Here is a detailed description of the SWD, according to an excellent report produced by the  UC Integrated Pest Management Website on Spotted Wing Drosophila: "Adults are small (2-3 mm) flies with red eyes and a pale brown thorax and abdomen with black stripes on the abdomen. The most distinguishable trait of the adult is that the males have a black spot towards the tip of each wing. 

Larvae are tiny (up to 3.5 mm), white cylindrical maggots that are found feeding in fruit. One to many larvae may be found feeding within a single fruit. After maturing, the larvae partially or completely exit the fruit to pupate."

Among you are those who are starting to ask the question, "What garden insecticide can I buy to stop this pest...."

Let me stop you right there. The cure may be worse than the problem. Limited research has been done on this new invader to California, and the chemical that so far has been found to best control the adult spotted wing drosophila is deadly to one the best "garden good guys" around, the honeybee.

The UC IPM Website says: "Although malathion...has been shown to control the adult SWD, coverage would need to be so thorough throughout the entire tree. 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. Application should be made about 2 weeks before harvest. Sprays must kill adults before they lay eggs. Malathion will not control larvae in fruit. 
An alternative to malathion with fewer negative environmental effects would be spinosad (Monterey Garden Insect Spray); however, it is not believed to be as effective against the fruit fly adults as malathion. Two sprays may be required at about 14 days and 7 days before harvest to get satisfactory control. 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."

Two better, safer options: dispose of infested fruit and set up traps, reports the UC IPM site

"Spotted wing drosophila attacks ripening fruit, and unfortunately is often not noticed in backyard trees until fruit is being harvested. Sprays at this time will not protect the crop, because maggots are already in the fruit. If only some fruit are infested, you can salvage some of the crop by harvesting the crop immediately and sorting, removing fruit with stings on the surface. Place infested fruit in a sturdy, sealed plastic bag and dispose of it in the trash. Also remove any fruit that has fallen on the ground and any infested fruit remaining on trees—this may reduce populations of flies that might infest next year's crops or later ripening varieties. In addition to placing infested fruit in the trash, it can also be buried. Composting may not be a reliable way to destroy eggs and larvae in fruit."

The report from UC goes on to say, "There is some evidence from research done in Japan in the 1930’s that traps can be used to manage SWD in backyard trees. Some trials on this method will be undertaken this summer. To try this method for yourself, make traps out of one quart plastic yogurt containers (with a lid). Drill 16 holes that are 3/16-inch in diameter around the top of the container. Bait each trap with a solution of 1/4 cup grape wine plus 1/4 cup water plus 3/4 teaspoon of molasses. In early May, about 1 month before harvest, hang 3 to 5 traps in a shady spot on the lower branches of the tree. Keep the traps up until harvest is completed. Refresh the bait if needed. These traps can also be used to detect SWD in your garden earlier in the season. Bait the trap with about an inch or 2 of white wine. Check the trap weekly for small flies with dark spots at the tip of their wings floating in the fluid. These are male SWD and will confirm that you have the pest."

The bottom line: good sanitation - cleaning up and disposing of fallen fruit and vegetables - goes a long way to thwarting many backyard pests.


  1. It's always a battle -- isn't it? The biggest problems for cherries in my backyard this year have been the brown rot (which you already know) -- and birds pecking into the few cherries we're getting off the Royal Ranier. As for the strawberries? The slugs have been simply voracious this year. But we continue to knock them down with cat food cans filled with beer. They prefer draft Budweiser -- FYI.

  2. We are recommending spinosad mixed with molasses.

  3. AAAAAHHHHHH!!!!! I just shuddered and had a flashback to my time in the genetics lab, attempting to cross-breed Drosophila melanogaster(the bane of biology students everywhere). One quick note, the spotted wings also like other soft-skinned/soft-fleshed fruit(per the UC article you referenced) such as plums, plumcots and nectarines. These are "fruit flies" after all. I felt the need to mention this as it seems every other yard in our neighborhood appears to have a Japanese plum tree in the front yard, including mine.

  4. The good news is that apparently the male flies are sterilized by temperatures above 86F, so damage may be limited on summer-ripening fruit. The host range is very broad, but my customers who had them on their cherries last year didn't have damage on nearby plums or peaches. The biggest concern will be cherries, strawberries, and cane berries.

  5. Just when I thought my cherry tree was perfect ...

  6. Spotted them in our tree in Sebastopol, Sonoma County, for the first time this year -- most of the crop damaged. Sigh...between the mildew brought on by the warm, late rains and the flies, the best crop in a couple of years is pretty much ruined. We'll hope for enough warm weather for the heat to kill off the adults before the plums and pluots ripen (if the leaf curl doesn't get them first)

  7. Just found these in our Bing cherries on Friday, June 4th in Orangevale. Over half the crop is infected with the little 'maggots'. It happened very fast during ripening and most infected fruit has 2-3 larva. Easy to tell by giving slight pressure and juice will squirt out of the holes used to lay eggs. None last year so hope it was just the weird weather and not a recurring problem.

  8. Thanks for posting this, however late I am to the party. My neighbor pointed out the little buggers in my cherries after I had scarfed half the crop...will try these traps this year. Hate having to share my wine but...worth it to have some cherries to share instead of destroy!

  9. I just found the disgusting maggots in my Montmorency cherries today, June 15th, 2013, in CENTERAL NEW JERSEY.

    My whole crop is trashed and I am LIVID.

    Malathion to the MAX next year.

    Luckily, my tomatoes are late harvest "pink cadillac" heirloom. Still gonna spray.