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Recommendations for Small Fruit Growers Now that Spotted Wing Drosophila has been Found in Pennsylvania

Posted: August 3, 2011

Now that spotted wing drosophila has been found in Pennsylvania (see news release at http://extension.psu.edu/ipm) at low populations, the question becomes what, if anything, should growers do about it? Spotted wing drosophila (SWD), a species of fruit fly, is problematic because tiny larvae or pupae of this pest can be present in the fruit when harvested, unlike immatures of other fruit flies. We really don’t know how high populations will become in Pennsylvania, but the risk to fruit crops will likely become greater as the season goes on. In other areas of the country where this pest is already well-established, fall raspberries and blackberries have probably suffered the most damage. Blueberries and summer raspberries have also had issues though to a lesser extent, and strawberries have probably been the least affected. An additional note of caution: So far in PA, most SWD were found in small fruit plantings near cherries, the crop in which SWD was first found, so growers with cherries nearby may want to be keep an eye out for SWD. Whether this is likely to be the situation in future years or not is not known. Management options will vary by crop, and are outlined below.
Kathy Demchak, Penn State Department of Horticulture
 

 

Monitoring:  If you want to monitor for this pest, instructions for how to use traps are given on numerous web sites, and a search of the term “spotted wing drosophila traps” will find this information.  Identifying SWD correctly isn’t completely straightforward, as other species that are similar to SWD have spots on their wings.  One of those was present in strawberry fields, possibly attracted to decomposing straw, but the spots were smaller and closer to the wing tip - anyone interested in what those looked like can check the Web for Scaptomyza spp. images.  Once the crop is ripe enough to be picked, the SWD may find the traps less attractive than the fruit.  To identify females, you need to check for a larger-than-normal ovipositor, since only the males have the wing spots. 

 

Cultural Management:  Any practice that you would use to minimize the presence of fruit flies in general would be in order.  As mentioned in an earlier article, SWD will continue to multiply in cull fruit, so unmarketable fruit should be removed from the field and destroyed or buried rather than remain in the field.  Strawberry fields should have been renovated as soon as possible after harvest, possibly with early cultivars being renovated sooner than usual rather than waiting for harvest of all cultivars to be finished.  Unfortunately, SWD will multiply on wild fruit as well as cultivated fruit, and thus wild stands of raspberries or blackberries may serve as reservoirs of SWD during the growing season, so our usual recommendations to remove wild raspberries or blackberries from near cultivated fields take on added importance.

 

Chemical Management:  Many pesticides have fairly good efficacy against SWD including some organic options.  Keep in mind that sprays for other pests such as brown marmorated stink bug may already be doing a pretty good job of controlling SWD, so it is highly likely that in many situations, additional sprays for SWD will not be needed.  Effective insecticides for which 2(ee) labels for spotted wing drosophila have been issued for berry crops are - in alphabetical order:

Danitol (fenpropathrin), labeled for strawberries, caneberries (raspberries, blackberries, etc.) and bushberries (blueberries, currants, etc.);

Delegate (spinetoram), labeled for caneberries and bushberries;

Entrust, Spintor, and Success (spinosad), labeled for strawberries, caneberries, and bushberries  (Entrust can be used in organic production);

Mustang Max (zeta-cypermethrin), labeled for caneberries and bushberries;

Pyganic (pyrethrins), which can be used on all berry crops and in organic production, but has very short residual activity.

 

      Pre-harvest intervals, re-entry intervals, and activity groups of these materials can be found in the Mid-Atlantic Berry Guide, online at http://pubs.cas.psu.edu/freepubs/MAberryGuide.htm or via printed copies in most county Extension offices.  Though insecticides from different activity groups should always be rotated with each other, rotation takes on additional importance with this pest since multiple generations could appear within a year making resistance development a concern.

 

Thanks to many people for help in monitoring for and documenting the presence of this pest in Pennsylvania, especially David Biddinger from PSU and Sven-Erik Spichiger from PDA.