Raspberry Worm

(Question)

We’ve had a large raspberry patch for over 20 years.
In September 2012 we noticed that some of the raspberries had a white worm about 4 mm long, inside the berry. We went to Sheridan Nurseries but they didn’t know how to treat this. We cut the canes back to ground level and added manure to the soil. We also noticed that some of the canes had a hole in the centre of the stock. Unfortunately, we have the same situation this year. Of course, we are afraid to eat the berries. We think we should dig out all of the plants but will there still be insects surviving in the soil? How do we treat the soil? Should we leave the ground fallow next year, in order to clear the latent bugs? Should we dispose of the removed canes in yard waste bags? We also grow tomatoes, zucchini, and butternut squash, none of which appear to be affected by the raspberry worm problem. Thanks for any information/suggestions

(Answer)

Sorry to hear that your raspberry crop is being affected.  An accurate identification of the “white worm” is necessary so the proper controls can be used.  The “worm” or larvae, that is small and white could be that of the common fruit fly (Drosophila melanogaster) or the new Spotted Wing Drosophila (SWD), it is impossible to tell the types of maggots apart.

SWD adults and maggots are very similar in appearance to the common fruit fly normally associated with over-ripe, decaying or damaged fruit. However, the presence of larvae in intact fruit prior to harvest should be viewed as suspicious to being SWD.

If the larvae have a discernible head, most likely it is the larvae of sap beetles or picnic beetles or raspberry fruitworm.  The vast majority of fruit flies are not SWD.

The University of Minnesota has a very good website that contains information on raspberry cane pests(i.e. Raspberry Cane Borer, Red-Necked Cane Borer, Raspberry Cane Maggot, Raspberry Crown Borer) and fruit pests (i.e. Raspberry Fruitworm, Picnic or Sap Beetles).  It also indicates what the pest looks like, the damage it can do and the controls to put in place.  https://www.extension.umn.edu/yardandgarden/ygbriefs/e216raspberry.html

 

Spotted Wing Drosophila

SWD is a new threat to tender fruit and berry crops, with raspberries and blackberries being the favorite food.  This is a new insect pest that can affect all berry crops and some tree fruits. It is native to Southeast Asia,  first showed up in California in 2008 and has now spread to Canada.

The SWD larvae are in the flesh of the fruit, not on the surface.   The name comes from the one obvious spot on adult males, on the leading edge of each wing close to the tip.  The females have unspotted wings and lays eggs in the ripening fruit.   The fly is very small, 1/10 of an inch long, light yellow or brown.  Once the eggs hatch, the larvae feeds on the inside of the fruit.  The larvae grows up to 1/8” (3.2 mm) long.

Cold weather will slow the spread of the fly, but as soon as it gets warm, the populations can explode.

The University of Guelph has an excellent website  https://www.omafra.gov.on.ca/english/crops/facts/pest-alert-swd.htm with many pictures on SWD.  They indicate that the larvae must be reared to adults for positive identification.

There are a few things that the home grower can do.

First, picking ripe fruit every day can be enough to fend off the fly. Refrigerate harvested fruit to 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 suspect SWD, and need to have samples identified, you should collect samples of infested fruit or trapped adults and submit them to Pest Diagnostic Clinic, University of Guelph

 

You may wish to refer to the folloeing websites for additional information: https://www.omafra.gov.on.ca/english/crops/facts/rasppest/rasppest.htm

https://extension.psu.edu/plants/vegetable-fruit/news/2011/spotted-wing-drosophila-2013-more-you-should-know