Fruit growers: Watch for spotted wing drosophila

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Alabama fruit growers should be on the lookout for a new and very damaging invasive pest that has become established in much of the Southeast and other parts of the nation. Spotted wing drosophila (SWD) have been especially damaging on strawberry, blueberry and blackberry/raspberry, as well as other soft skinned fruit.

According to Georgia Extension Entomologist, Dr. Dan Horton, Georgia growers experienced a very serious SWD infestation in their strawberries near the end of their 2012 season. “SWD is the most significant “new” fruit pest observed in my career. I’ve been at UGA 30+ years.”
Female SWD preferentially lay their eggs in ripe and ripening fruit, unlike nearly all other Drosophila (fruit fly) species which are common on over-ripe or decaying fruit. The resulting larvae feed on the fruit, causing direct damage, and may also be present at harvest, contaminating the product, risking the sale of “wormy” fruit to clientele and potentially devastating crop losses.
In Alabama, SWD specimens have been confirmed from six counties, however it is believed by entomologists that the pest may now be present throughout the state.
 
Dr. Charles Ray, Extension Entomologist with the Alabama Cooperative Extension System explains “We have had SWD in AL for 2 full years, first found in 2011 in Coosa County. And since then we’ve had confirmed specimens from Macon, Lee, Coosa, Elmore, DeKalb and Cullman Counties. We had larvae in blackberries in 2011 but no adults were submitted for positive identification. I would appreciate any suspect adult specimens from additional counties for both verification and our records."
Dr. Hannah Burrack, North Carolina Extension Entomologist, has worked closely with growers in North Carolina since SWD entered their state several years ago. She states that at present trapping SWD as a means to time insecticide applications has not been effective, so the current recommendation to manage SWD is through regular, preventative insecticide applications beginning when the fruit begin to change color.
 
Weekly sprays are advised, beginning as soon as fruit begin to ripen. Treatments should be reapplied in the event of rain or applied more frequently than weekly if SWD damage develops. Insecticide classes should be rotated with each application to avoid resistance.
Dr. Horton explains, “Even the good control received with 7-day preventative treatment schedule control will on occasion be less than perfect. Strawberry, blueberry and blackberry growers who do not spray aggressively are risking their crops.” Once a crop is infested, two weeks’ harvest can be lost before the infestation can be cleared up with insecticides.
Dr. Burrack adds, “Even with aggressive, insecticide intense management programs SWD can cause total crop loss if the environmental conditions are right (rainy, cool, and available hosts).”
Dr. Donn Johnson, Arkansas Extension Entomologist has an excellent publication, “Biology, Identification and Management of Spotted Wing Drosophila” online here.
Fruit sampling is recommended for detection of SWD larvae in fruit with a minimum of 30 fruit sampled from each field or variety being harvested, at each harvest. There is currently a zero tolerance policy for SWD larvae in marketed fruit, so any detection is cause for grower concern.

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