raspberry worms

Asked July 25, 2020, 6:54 PM EDT

For 4 years now I've tried to raise some eating berries. 30-60% have little white worms.I have sprayed early and after berries. How do I keep the larva from hatching or ???>Than k you-Dan

Multnomah County Oregon

1 Response

Hi Dan,

Many gardeners are complaining about worms in their raspberries. The small, white worms are likely the larvae of the spotted wing drosophila, Drosophila suzukii. Spotted wing drosophila (SWD) is a small vinegar fly with the potential to damage many fruit crops. Unlike most other vinegar flies that require damaged fruit to attack, the SWD does not. The adults are small, yellowish-brown flies. Males have distinctive dark spots on their wings, hence the name spotted wing Drosophila. Female adults have serrated, saw-like ovipositors [ōvəˈpäzədər] -- a tubular organ through which a female insect (or fish) deposits eggs. She will cut a slit and lay eggs in healthy fruit. SWD larvae are white, 1/8-inch-long maggots.

The spotted wing Drosophila feeds on soft, thin-skinned fruit. Their preferred food choices are raspberries (especially fall cultivars), blackberries, and blueberries. However, they also feed on grapes, strawberries, cherries, and Aronia berries.

An abridged excerpt from the University of California Statewide Integrated Pest Management Program (IPM).

“Traps can be used to detect and monitor SWD adults. Commercial fruit fly traps are available or you can make traps (see attached photograph) out of 1-quart plastic yogurt (or similar) containers that have a lid. Drill 10 to 16 holes that are 3/16-inch in diameter around the upper side of the container for fly entry. Bait the trap with 1 to 2 inches of pure apple cider vinegar; avoid flavored apple cider vinegars. Add a drop of unscented liquid dishwashing soap to break the surface tension so the flies will drown. Hang the trap in the shade in your cherry tree or near your berries in early May or well before fruit begins to ripen.

Check the trap weekly for small flies with dark spots at the tip of their wings floating in the fluid. These are male spotted wing drosophila and will confirm that you have the pest. Put fresh apple cider vinegar and a drop of soap in each week.

Chemical Control

Before you spray, confirm that you have SWD in your area by hanging out traps or checking fruit. Sprays must be timed to kill adults before they lay eggs, as sprays will not control larvae already in the fruit. Always read product labels to make sure pesticides are registered for use on the fruit or berry you are treating.

If monitoring indicates a need to spray, the 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. A second application may be needed 7 to 10 days later. In the case of indeterminate fruiting berries such as raspberries or strawberries, sprays might need to be repeated to keep populations low during summer and fall. You can use monitoring traps to help you decide if and when additional sprays might be needed. Be sure to wait for the interval specified on the pesticide label before harvesting fruit.

The insecticide spinosad (e.g., Monterey Garden Insect Spray) is effective and has the least negative environmental effects of currently available products. Some spinosad products are sold to be applied with a hose-end sprayer, but a compressed-air sprayer will give more reliable coverage.

The organophosphate insecticide malathion also will control spotted wing drosophila, but 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 target plant and avoid drift and runoff. Using improper applications also can result in injury to cherry trees. Because of the potential negative impact of malathion in the garden, use it only where you are certain you will have a spotted wing drosophila infestation, either because you had a problem last year or from trapping and positively identifying insects this season as SWD.”

Other effective insecticides for which are label specific for spotted wing drosophila have been issued. These are registered on raspberries and blackberries: Danitol (fenpropathrin); Delegate (spinetoram); Entrust and Success (spinosad); Mustang Max (zeta-cypermethrin); and Pyganic (pyrethrins). Other materials registered on caneberries for other pests are also effective on SWD.

Another effective SWD trap is from Cornell University – Fermenting Dough.

According to the University of Minnesota Extension, during minor infestations, infested fruit can be processed into wine or jelly. During severe infestations, the fruit is too rotten to be processed.

Of course, you could eat the fruit quickly and not look! (They don’t affect the flavor.)

Good luck and happy gardening.