Spotted Wing Drosophila Part 4: Management

Spotted wing drosophila (SWD) is a vinegar fly that lays eggs in fruit as it ripens, so its larvae may infest fruit at harvest. Growers should monitor for this pest, correctly identify it, and take steps to minimize its population through all available means.

Cultural Management

Harvest thoroughly

Remove all ripe and cull fruit 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. In crops harvested many times, such as raspberries, harvest frequently--possibly daily.

Dispose of unwanted fruit

Keep flies from feeding on or hatching from old fruit. SWD and other fruit fly species will multiply in cull fruit, so remove and destroy it, or bury it at least 2 feet deep. Crushing the fruit does not hamper SWD emergence.

SWD can emerge from fruit in compost piles, and its development may accelerate in warm areas of the pile. Thus, composting infested fruit is not recommended. However, research in Oregon has found that bagging fruit in plastic or covering it with plastic and exposing it to full sun for a week kills all eggs and larvae.

Field management

With Pennsylania's diverse landscape, it is difficult to manage the landscape in a way that causes a reduction of SWD to any significant degree.  The only exception to this is when fields of berry crops are surrounded by large areas of agronomic crops, in which case SWD numbers have been lowered.

Trapping

Traps are for detecting adult SWD and initiating control measures, not for control. Research in Japan indicated that intensive trapping (60-100 vinegar traps per acre) decreased SWD numbers. In Pennsylvania, intensive trapping did not reduce SWD numbers noticeably.

Exclusion

Screening with extremely fine mesh (less than 0.98 mm, 18 mesh or finer) can protect crops especially in tunnels. However, venting can be problematic. Increasing airflow and introducing pollinators, if the crop is blooming, will be required.

Biocontrols

Recently efforts have been underway to introduce a parasitoid wasp that parasitizes SWD specifically, but this work is still in early stages.  However, a second parasitoid wasp is establishing in the region on its own, and has been found to parasitize up to 40% of SWD larvae on some farms and in wild host plants.

Chemical Management

The cost of spraying is much less than the cost of potential crop loss to SWD. Currently, pesticide spray recommendations target adults to minimize the number of eggs laid and thus larvae in fruit. Pesticides in four activity groups--pyrethroids (IRAC activity group 3), spinosyns (group 5), organophosphates (group 1B), and carbamates (group 1A)--have shown fairly good efficacy against SWD adults. Neonicotinoids have not been very effective against adults, though they may have some effectiveness against eggs and larvae. Pesticides in different chemical classes must be used; resistance development in SWD is a concern.

SWD prefers high humidity, so some of the adults will be in the densest foliage or near ground level. Poor spray coverage will decrease control; missing some adults will allow populations to re-escalate. Determine adequacy of spray coverage through the entire canopy by using paper spray targets. Use adequate volumes of spray solution and pressure. Use a higher volume of water than usual or include a spreader/sticker surfactant to increase coverage. If using an airblast sprayer, drive every row middle to obtain adequate coverage. Raspberry and blackberry growers relying on backpack sprayers should consider a trellising system that opens up the canopy to improve spray access. Monitor with traps and check fruit to evaluate your spray program's effectiveness.

Applying sprays before SWD is present may needlessly decimate populations of beneficial predatory insects and pollinators. Check traps daily as harvest approaches and initiate sprays if flies are captured. Once sprays are needed, choose spray materials and time applications to protect pollinators. Check the first ripe fruit very closely--maintaining a clean planting is easier than trying to regain control.

The table below lists pesticides that have shown good effectiveness for SWD control.  Note that spotted wing drosophila does not appear on the labels of all products listed; when that is the case, whether the material can be used for spotted wing drosophila depends on regulations in each state.  Not all products are registered for use in all states.  If from outside of PA, consult the label and your state’s registrations for products that may be used in your location.  Be sure to follow instructions on the label of the product in your possession, as it is a legal document outlining allowed uses, and supersedes information provided here.  (R) following the pesticide name indicates that the material is a restricted-use pesticide.

(d = days; h = hours; --- = not labeled for use on this crop). See individual product labels for details

*E = excellent, G =  good; based on rankings at SWD rankings - 2021 

References

Beers, E. H., et al. "Developing Drosophila suzukii management programs for sweet cherry in the western United States." Pest Mgt. Sci. 67, no. 11 (2011): 1386-95.

Bruck, D. J., et al. "Laboratory and field comparisons of insecticides to reduce infestation of Drosophila suzukii in berry crops." Pest Mgt. Sci. 67, no. 11 (2011): 1375-85.

Cini, A., et al. "A review of the invasion of Drosophila suzukii in Europe and a draft research agenda for integrated pest management." Bulletin of Insectology 65, no. 1 (2012): 149-60.

Dalton, D. (submitter). "Biology and management of spotted wing drosophila on small and stone fruits year 1." Corvallis: Oregon State University, 2012.

Isaacs, R., et al. "Spotted wing drosophila management recommendations for Michigan raspberry and blackberry growers." East Lansing: Michigan State University, 2012.

Lee, J. C., et al. 2011. In Focus: Spotted Wing Drosophila, Drosophila suzukii, across perspectives. Pest Mgt. Sci. 67:1349-1351.

"Spotted wing drosophila." Corvallis: Oregon State University, 2013.

Walsh, D. B., et al. "Drosophila suzukii (Diptera: Drosophilidae): Invasive pest of ripening soft fruit expanding its geographic range and damage potential." J. Integrated Pest Mgt. 2, no. 1 (2011): G1- G7.

Prepared by K. Demchak, D. Biddinger, and B. Butler. Photo courtesy of Alex Surcică.

Parts 1, 2 and 3:

Spotted Wing Drosophila Part 1: Overview and Identification

Spotted Wing Drosophila, Part 2: Natural History

Spotted Wing Drosophila, Part 3: Monitoring