SWD Update 1 May 2012

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Spotted Wing Drosophila Update
By the SWD Team

May 1, 2012

Crop update

There are 1,900 acres of strawberries producing approximately 24 million lbs of fruits in Oregon, of which 80% is processed with the remaining for the local fresh market. The harvest season typically starts at the beginning of June and lasts about 4 weeks. With day-neutral cultivar such as ‘Albion’, harvest season can be extended into September. For most strawberry growers, SWD hasn’t been a problem because populations haven’t peaked until late-July in the past two seasons. However, for day-neutral production, chemical application may be needed to protect fruits against SWD.

SWD season update

Observations in Oregon since 2009 indicate SWD overwinters as an adult. SWD numbers were significantly higher after strawberry harvest in 2011 as compared to 2010, but trap counts steadily declined to reach 0 flies per trap in both 2011 and 2012 during April, most likely due to cold temperatures, starvation, attrition, winter predation, and “running out of gas”. Figures below show average fly counts (8 traps) in strawberry field from November to April in Mid-Willamette Valley.


(note the different scale of the y-axes in the above two figures)

SWD research in strawberry

SWD was first recorded in North America in August 2008 on strawberries and caneberries in California. To date, little economic damage from SWD has been reported in California or Oregon strawberries, which could be partially due to low SWD populations during early-season strawberry harvest and short harvest intervals. In laboratory studies, SWD developed in both green and colored strawberry fruits with increased development in blush and red colored fruits. SWD appear to prefer ripe to overripe fruit. SWD development in strawberry fruits also was affected by fruit characteristics. Increase in fruit firmness seems to reduce SWD development, while increase in fruit Brix seems to favor SWD development. Because Oregon strawberries largely have not been affected by SWD, most chemical efficacy studies have been devoted to other berry crops.

SWD control in strawberry

Monitoring: Begin immediately prior to blush of color through harvest. Place apple cider vinegar (ACV) traps, concentrating on field margins, inside strawberry rows to provide some shade. Replace ACV bait weekly and check for SWD presence. For detailed monitoring information, visit spottedwing.com.
Control: Currently, SWD control relies primarily on insecticides. Please consult the PNW pest management handbook for more details regarding control of SWD.



Editor: Wei Yang

Contributing authors: Amy Dreves, Denny Bruck, Jana Lee, Jimmy Klick, Joe DeFrancesco, Vaughn Walton