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Spotted Wing Drosophila Management

Posted: June 22, 2012

You may be getting tired of hearing about Spotted Wing Drosophila (SWD), but adults are being found in traps in the southeastern corner of Pennsylvania and eastern Maryland, and its larvae have been found in summer raspberry fruit in Maryland (along with lots of other kinds of larvae in all sorts of berries).
K. Demchak and D. Biddinger, Penn State; and B. Butler, University of Maryland

 

A brief recap of where we stand on this pest….  In the past few years across the U.S., SWD populations have been highest in late summer and early fall.  In Pennsylvania and Maryland in 2011 when it was first found here, late season fruit crops such as fall raspberries, late-season blackberries, and day-neutral strawberries suffered the most damage, though it was also found in other fruit crops such as blueberries, summer blackberries and raspberries, cherries and grapes. 

Since we know SWD is here already, here are the management options.  Utilizing all means of management - including cultural and chemical options - is recommended. The most suitable strategies for any farm will vary with the crop and circumstances. 

Cultural Management

Harvest practices.  Harvest thoroughly.  All ripe and cull fruit should be removed from the planting.  Paying someone to remove old fruit may be worth the cost.  In pick-your-own plantings, consider rewarding customers for removing unmarketable berries as well as sound ones.

In crops that are harvested many times such as raspberries, keep harvest intervals short, and pick the fruit as soon as possible.  In some raspberry plantings, this strategy alone has arrested problems with SWD - even without applying insecticides – as long as the entire planting was kept clean.  On other farms, this strategy alone has been insufficient.  This may be related to the presence of other host crops. 

Disposal of unwanted fruit.  Dispose of unwanted fruit in a way that will keep fruit flies from feeding on it or from hatching from it. SWD and other fruit fly species will continue multiplying in cull fruit, so remove cull fruit from the field and destroy it, or bury it a minimum of 2 feet deep. Crushing the fruit does not hamper SWD emergence from it.

SWD can easily multiply in and emerge from fruit that is below critical temperatures in compost piles. In fact, SWD development may be accelerated in warm areas of the pile.  Thus, composting fruit is currently not recommended.  However, research in Oregon has found that sealing fruit in plastic bags or on the ground with plastic and then exposing it to full sun for at least a week kills all eggs and larvae. 

Field management.  SWD will multiply on wild fruit (raspberries or blackberries in hedgerows, mulberries, wild cherries, etc.) as well as cultivated fruit, and thus wild stands of these hosts can be reservoirs of SWD.  Wild plants also serve as sources of diseases, and even though they may provide refuge and food for pollinators, their removal is generally recommended.    

Renovate June-bearing (short-day) strawberry fields promptly.  Though SWD has not been problematic on June-bearing strawberries yet, SWD could multiply on strawberries that remain in the field after harvest.  Early cultivars could be renovated sooner than late cultivars.
 
Trapping.  Traps are typically used to detect adult SWD and determine whether control measures are needed, and are not intended to provide control (see last month’s article on how to monitor for SWD). However, research in Japan indicated that intensive trapping (60 to 100 vinegar traps per acre) decreased SWD numbers.   A commercial manufacturer of SWD traps recommends using traps at the end of the season to mop up late-season SWD that could overwinter.

Exclusion.  Screening may protect individual plants or crops in protected culture such as high tunnels or greenhouses. In Japan, using extremely fine mesh with openings less than 0.98 mm = 0.039 inches wide (18 mesh or finer) protected blueberries.  If screening is used, venting can be problematic.  Some means of increasing air flow such as using a fan will be required, as will pollinator introduction if the crop is in bloom.

Biocontrols

Several predatory insects feed on SWD adults and pupae, but not yet in sufficient quantities to provide significant control.  A tiny predatory wasp that parasitizes SWD pupae is present in the Pacific Northwest and mid-Atlantic region and thus may be found in other regions as well.  Research is needed to understand whether and how this species may be utilized in long-term SWD management.

Chemical Management

Presently, pesticide spray recommendations target adults to minimize the number of eggs laid and thus larvae in fruit.  Pesticides in three activity groups – pyrethroids (IRAC activity group 3), spinosyns (activity group 5), and organophosphates (activity group 1B) have shown fairly good efficacy against SWD adults.  Neonicotinoids have not been very effective against adults, although they may have some effectiveness against eggs and larvae in the fruit.  More research is necessary before recommendations are made for the control of immature stages.

Using pesticides in different chemical classes is a must; resistance development is very likely since many generations of SWD occur per year.   In fact, resistance to natural pyrethrins has already been reported in West Coast SWD populations. 

Applying sprays without knowing whether SWD is present is not recommended, as populations of beneficial predatory insects and pollinators may be needlessly decimated.  Make sure you know SWD is present before you spray for it.

Using materials for which a FIFRA 2(ee) label for SWD management has been issued is prudent, as rates for SWD control will be listed on the label and effectiveness of the product has been established. Most states also allow use of other products that do not have SWD listed on the label, as long as the use pattern (crop, rate, timing, etc.) is the same as for other pests listed, label restrictions do not preclude the use, and a recommendation for use has been made by a company or individual. However, some other states (NY for example) allow products to be targeted against only pests listed on the label and therefore must have a 2(ee) exemption.  Laws and their interpretations are subject to change.

The following table lists insecticides that have been effective against SWD for the 4 crops at greatest risk of damage from SWD: raspberries, blackberries, strawberries (day-neutral varieties), and cherries.  Materials with a long pre-harvest interval may be used immediately post-harvest to knock back populations that will feed on any remaining overripe or dropped fruit. 

Pyrethroids and pyrethrins (IRAC activity group 3A)

Data for Pyrethroids and pyrethrins (IRAC activity group 3A)

Pre-harvest interval (days)
Trade name (Active Ingredient) Raspberries Blackberries Strawberries Cherries Effectiveness Length of Residual Activity
Brigade (bifenthrin) 3 3 0 X Excellent 7 days
Danitol (fenpropathrin) 3* 3* 2* 3* Excellent 7 days
Baythroid (beta-cyfluthrin) X X X 7* Excellent 7 days
Mustang Max (zeta-cypermethrin) 1* 1* X 14* Excellent 7 days
PyGanic (pyrethrins) ** 0 0 0 0 Good*** 0-2 days

Spinosyns (IRAC activity group 5)

Data for Spinosyns (IRAC activity group 5)

Pre-harvest interval (days)
Trade name (Active Ingredient) Raspberries Blackberries Strawberries Cherries Effectiveness Length of Residual Activity
Delegate (spinetoram) 1* 1* X 7* Excellent 5-7 days
Radiant (spinetoram) X X 1 X Excellent 5-7 days
Spintor (spinosad) 1 1 1 7 Excellent 5-7 days
Success (spinosad) 1* 1* 1 7* Excellent 5-7 days
Entrust (spinosad) ** 1* 1* 1 7* Excellent 3-5 days

Organophosphates (IRAC activity group 1B)

Data for Organophosphates (IRAC activity group 1B)

Pre-harvest interval (days)
Trade name (Active Ingredient) Raspberries Blackberries Strawberries Cherries Effectiveness Length of Residual Activity
Malathion (malathion) 1 1 3 3 Excellent >7 days
Diazinon (diazinon) X X 5 21 Excellent >7 days

* 2(ee) labels have been issued for use against SWD on this crop in PA.
**May be used in organic production.  The REI is 12 hours even though the PHI is 0 days.
*** Provides knockdown of non-resistant populations, but has little to no residual activity.

“X” = the material is not labeled for use on the crop.

Residual activity has sometimes been reported to be shorter than what is listed below, so a close watch of traps for return of adults will be needed.  All materials listed work on SWD primarily by contact, so spray coverage should be thorough.  Use a higher volume of water than usual or include a spreader/sticker surfactant to increase coverage. 

References

Beers, E. H.  R. A. van Steenwyk, P. W. Shearer, W. W. Coatest, and J. A. Grant.  2011.  Developing Drosophila suzukii management programs for sweet cherry in the western United States.  Pest Mgt. Sci.  67(11): 1386-1395.

Bruck, D. J., M. Bolda, L. Tanigoshi, J. Klick, J. DeFrancesco, B. Gerdeman, and H. Spitler. 2011. Laboratory and field comparisons of insecticides to reduce infestation of Drosophila suzukii in berry crops.  Pest Mgt. Sci. 67(11):1375-1385.

Cini, A., C. Ioriatti, and G. Anfora.  2012. A review of the invasion of Drosophila suzukii and Europe and a draft research agenda for integrated pest management.  Bulletin of Insectology. 65(1):149-160.

Dalton, D. (submitter).  2012.  Biology and Management of Spotted Wing Drosophila on Small and Stone Fruits Year 1. 

Isaacs, R. Tritten, B., S. Van Timmeren, J. Wise, C. Garcia-Salazar and M. Longstroth.  Spotted Wing Drosophila Management Recommendations for Michigan Raspberry and Blackberry Growers. 

Lee, J. C., D. J. Bruck, A. J. Dreves, C. Ioriatti, H. Vogt, and P. Baufeld.  2011.  In Focus: Spotted Wing Drosophila, Drosophila suzukii, across perspectives.   Pest Mgt. Sci.  67:1349-1351.

Oregon State University.  Spotted wing drosophila.

The above information was reviewed by Ed Rajotte, Penn State, and Greg Loeb, Cornell University.

 

Contact Information

Kathy Demchak
  • Senior Extension Associate
Email:
Phone: 814-863-2303