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Green Speak

Horticulture topics from gardens to lawns and then some.

Spotted Wing Drosophila Update for West-Central Illinois

If you are a Master Gardener or have been around me at all this growing season, you have probably heard me mention spotted wing drosophila. I have spent much of the summer monitoring population levels of this new invasive pest from Asia. Spotted wing drosophila (SWD) looks similar to the small vinegar flies (fruit flies) that are typically found on fermenting fruit and vegetables. However, SWD have a lifecycle that makes them a significant pest of our small fruits- raspberries, blackberries, blueberries, elderberries and grapes are at the greatest risk. Other crops SWD targets are stone fruits (cherry, nectarine, peach) and high tunnel tomatoes to name a few. The SWD female uses a serrated egg-laying organ called the ovipositor to cut a slit in the fruit and lay her eggs. These eggs hatch into small white larvae that then feed on the fruit. As you can read, unlike their vinegar fly cousins, SWD have the ability to attack intact ripening fruit. One easy way to identify SWD is a dark spot on both wingtips of the males. Researchers believe that these pests overwinter in wild hosts such as pokeweed, dogwood, crabapple, wild grape, and several others. (Pinero & Byers, 2013) Although, scientists up north (Wisconsin and up.) are not sure if SWD can survive that region's harsh winters.

If you grow any of the above listed fruits, you may have been one of the unlucky souls to have already come across SWD. In my traps I did not capture a significant amount until mid-August in a peach tree. From that point on, I was able to capture considerable numbers of SWD in grapes and blackberry brambles. Some reasons for this late appearance could be due to our cool wet spring and early summer, or it just takes time for their number to build over the summer. 2014, if the weather cooperates, will be a more telling year of how this new pest will behave in our gardens. As of now, the trend of their delayed population growth toward the end of the season suggests our early season fruits such as strawberry, are safe. More observation and monitoring are needed, but I believe this pest has the potential to have devastating effects on our small fruit crops.

Cultural controls for homeowners:

Exclusion – Netting can be used as an exclusion technique. Make sure to apply netting before the fruit begins to ripen and secure it tightly at the bottom so no flies can enter below. Ensure you have a mesh size small enough to prevent SWD from entering.

Remove native hosts – If you have several edge species of dogwood, honeysuckle, or wild blackberries, removing these will reduce the amount egg laying sites.

Dispose of infested fruit – Make sure your harvests are timely and don't allow fruit to rot on the vine or ground. Collect over-ripe or infested fruit in a plastic bag, seal it and solarize it by placing it in the hot sun. You can also bury the fruit, but composting will not kill the larva, so keep it out of the compost pile.

For more information on SWD and chemical controls feel free to contact me at cenroth@illinois or your call local Extension office.

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