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Fly is likely cause of worms in raspberries [UPDATED]

Published 4:15am Monday, June 3, 2013 Updated 6:18am Monday, June 3, 2013

If you had a little protein in your fruit last fall, you were not alone. This is going to be a problem for any fruit that ripens from mid-July until fall. It is caused by the spotted wing drosophila fly.

Native to Southeast Asia, they first showed up in California in 2008 and now have spread clear to Canada. Several local raspberry growers noted tiny white maggots in their crop last summer.

This fly is very small, 1/10 of an inch long, light yellow or brown. The adult males have one obvious spot on the leading edge of each wing close to the tip, and two black bands on each front leg.

The females have unspotted wings. She has a saw-like ovipositor that lays eggs in the ripening fruit, mainly late season raspberries, black berries and day neutral strawberries.

She can also attack blueberries, cherries and grapes. The tissue around the egg laying site will discolor and start to decay in a few days.

The larvae hatch and begin to feed, growing up to one-eighth of an inch long inside the fruit, causing the eater a nasty surprise.

Cold weather slows the spread of the fly, but as soon as it returns to the 70’s, the populations virtually explode resulting in 8 or 9 generations a year.

There are a few things that the home grower can do. First, remove any wild hosts. These are wild raspberries, mulberries, dogwoods, cherries, viburnums and even pokeweed. The fly loves dense foliage, high humidity’s and moderate temperatures.

Picking ripe fruit every day can be enough to fend off the fly. Refrigerate harvested fruit to — at the very least — slow the development of the eggs and kill some of the larvae that haven’t yet hatched.

Don’t compost culls or overripe fruit as the compost doesn’t get hot enough to kill the eggs.

Trapping will let you identify that you have the fly but is ineffective at controlling the population.

If you must spray, try to find Pyganic or Entust both are insecticides approved for organic growers. The latter is a spinosad.

The early populations are already resistant to natural pyrethrins.

This is going to be a problem for some time. Pity the poor commercial grower as most people do not want worms in their fruit.

Maybe they can promote this as an easy way to get extra protein. Yech and ick.

If you would like more individual help, call the Extension Office at 218-998-8760 or stop in at 505 South Court St., Fergus Falls.

You may also call the radio station (1250 AM) each Saturday morning or stop by City Café and Bakery after the radio show to ask a master gardener.


Bev Johnson is a master gardener in Otter Tail County.





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