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SWD and sour rot of grapes

SWD populations are building up and the warm, humid weather of late summer and early fall is very favorable for spotted wing. Any fruit hanging will be at risk of infestation. Not until late November will the majority of female SWD no longer carry eggs, as they prepare for overwintering.

Wayne Wilcox, grape pathologist, Plant Pathology & Plant-Microbe Biology Section, Cornell University, sent this alert out, “…the warm, humid conditions are ideal for the yeast and bacteria that cause sour rot, not just for SWD. These weather conditions strongly favor sour rot, since sour rot appears to require three components: (1) yeast, (2) bacteria, and (3) fruit flies—either the “everyday” fruit fly Drosophila melanogaster or SWD Drosophila suzukii. SWD is NOT required for sour rot to occur and, indeed, we do not typically find it associated with sour rot in the Finger Lakes region, although sour rot can be common here.

Recent research information on grape sour rot from Wayne’s program was summarized last spring on pages 47-57 in GRAPE DISEASE CONTROL, 2016. Included in these pages are details on research trials in field and lab, management tactics, efficacy of fungicides and insecticides, and impact of training systems on the development of sour rot in wine grapes. For those of you growing wine grapes, advising growers on sour rot, or simply interested in a complex and difficult to control disease, these pages are definitely worth a read.

An interesting observation came in yesterday from a wine grape grower in the Finger Lakes where the region has been plagued by drought. Several inches of rain had fallen in their area recently, causing many berries in the cluster to swell and crack. This is an ideal setting for infestation by SWD, other Drosophila species, and fruit rot pathogens.

Herkimer County finds SWD

On August 20th, traps being monitored by Bernie Armata, Extension Educator, Herkimer County Cornell Cooperative Extension, caught 5 male SWD. These traps were in a blueberry planting and shortly after receiving the trap catch news, the grower did salt flotation on a fruit sample, confirmed larval presence and shut down harvest.

Two male SWD on a blueberry, photographed in early September 2013. SWD populations typically build to very high levels in late summer and early autumn.

Two male SWD on a blueberry, photographed in early September 2013. SWD populations typically build to very high levels in late summer and early autumn.

The good news is the grower was able to harvest 90% of their blueberry crop before SWD arrival.

Bernie adds that, “It would seem that SWD arrive in Central NY a bit later than some other areas of the state, as this has been the case two out of the last five or six years.”

SWD populations are building up. Any fruit hanging will be at risk of infestation. Not until late November will the majority of female SWD no longer carry eggs, to prepare for overwintering. If you have fruit in protected culture (high tunnels), be especially vigilant. SWD management during late summer and early fall must include insecticides to protect fruit from infestation, unless effective exclusion netting is being used.

2016 Trap Network Wrap-up

All SWD trapping locations have caught SWD. First trap catch occurred over a nine- to ten-week-long period, from June 8 to August 13. SWD was caught earlier this year than in prior years, but the hot and extremely dry weather across New York State appears to have benefited berry crops, which suffered lower infestation rates in July than might have been expected from the early arrival of SWD.

Distribution map for SWD, as determined by the SWD network operated by 25 Cornell University and Cornell Cooperative Extension scientists in 25 Counties, monitoring 117 traps.

Distribution map for SWD, with data contributed by the SWD network operated by 25 Cornell University and Cornell Cooperative Extension scientists in 25 Counties, monitoring 117 traps.

Twenty-five scientists monitored traps in 25 Counties this year. A total of 117 Scentry traps were deployed in the network, primarily in raspberry (summer and fall) and blueberry. The first trap network site to report SWD trap catch was in Suffolk County, Long Island. At about the same time, SWD was caught at a research location in the Finger Lakes region.

Although SWD might show up around the same time each year in a particular location, this doesn’t often hold true. For instance, the location in 2015 at which my program caught SWD first was among the last of our monitoring locations to catch SWD this year.

The long length of time, 66 days, over which first trap catch reports came in from across NY in 2016 and in prior years (56 days in 2015, 56 days in 2014, 76 days in 2013) provides evidence that SWD arrival across NY isn’t synchronous. For this reason, in addition to trap catch reports, growers should consider crop maturity and crop susceptibility to infestation when formulating management decisions.

With most of NY in the grips of a drought – abnormally dry, moderate drought, severe drought, and extreme drought as of August 25 – this could keep SWD population growth in check. The US drought outlook shows likely drought removal in the Hudson Valley region, but drought will likely persist in western NY and Suffolk County.

It is easy and fast to check fruit for SWD infestation. Leaky fruit and dull sunken areas on fruit point to infestation. A quick salt flotation assay provides a good measure of SWD infestation in fruit—time well spent. Consult the Cornell Fruit Resources SWD pages for more information on dealing with this invasive pest.

Updates from Global SWD Research

Spotted wing drosophila (SWD) is native to South East Asia. It was first recorded as an invasive species in Hawaii in 1980, and in both California and parts of Europe in 2008. Since then it has spread rapidly throughout temperate North America and Europe, mainly due to global trade combined with an initial lack of regulatory controls. Its annual rate of range expansion has recently been estimated at approx. 1000 km (~620 miles) per year, and it is now established in parts of South America and the Middle East.

As a result of its global economic impact, spotted wing drosophila is the target of an intense global research effort encompassing various aspects of its biology and control. This article summarizes the results of some of this recent research that offers potential for the development of future pest management strategies. Please note that these reports do not constitute recommendations at this stage.

Summary of life-cycle

Spotted wing drosophila overwinters as a specialized (darker) adult morph that has greater cold tolerance than the summer form. Overwintered flies emerge in spring and feed on nectar from early flowering weeds and crops. Overwintering adults may live for more than 200 days, but the longevity of the summer form is considerably less. Reproductively mature female flies lay eggs in the ripening fruits of a wide range of host plants, including many wild, uncultivated species. Each female may produce 100–400 eggs, laying approximately 20 per day (depending on host availability and environmental conditions).

Recent research from Italy has shown that spotted wing drosophila can complete its lifecycle at temperatures as low as 53 °F; however, adult activity is highest at temperatures between 68 and 77 °F, and is reduced at temperatures above 86 °F. Adults are most active at dawn and dusk.

Larvae develop inside the fruit and complete their development in 3-13 days (depending on temperature). Pupation can occur in the fruit or in the soil, and the entire life-cycle can be completed in approx. 7–10 days (again, depending on temperature). Under optimal conditions, up to 13 generations per year are possible, although in the US and Canada 3–9 generations are more typical. Canadian research suggests that the lower lethal temperature for adult flies is in the region of 19 °F, although cold tolerance depends on the extent of prior exposure to fluctuating cool temperatures. There is evidence to suggest that females are more cold-tolerant than males.

Recent research results

i. Host plants

Fruits of susceptible host plants are liable to attack as soon as the fruit begins to soften and show color. Research with both raspberries and blueberries has shown that green, hard fruits are not at risk. The likelihood of egg-laying increases as the force needed to penetrate the fruit decreases: hence egg-laying is consistently high in raspberry and other thin-skinned fruits. In a recent US study, calcium treatments applied to blueberries in a field experiment produced firmer fruits that harbored fewer SWD eggs than fruits from untreated plots.

The wide host plant range of spotted wing drosophila can influence population levels at the landscape scale. In one US study, the abundance of wild hosts in nearby woods and hedgerows was implicated in the increased early-season risk of spotted wing drosophila in adjacent raspberries. However, it did not appear to influence the subsequent rate of population development in those crops.

As an indication of the wide host plant range of spotted wing drosophila, in recent field surveys in Europe, more than 24,000 adult flies successfully emerged from the fruits of 84 plant species from 19 different plant families, 38 of which were non-native species. The highest infestations were found in species of Cornus (dogwoods), Prunus (relatives of stone fruits such as cherries, plums, etc.), Rubus (raspberries, blackberries, and relatives), Sambucus (elderberry) and Vaccinium (blueberries and relatives). US research has shown a similarly wide range of hosts, including many of the above, as well as Morus (mulberry), edible blue honeysuckle (also known as haskap or honeyberry), and some common herbaceous weeds such as Solanum dulcamara (bittersweet nightshade). In Europe, spotted wing drosophila has also been found infesting mistletoe berries (Viscum album) – probably one of the earliest host fruits available for spring egg-laying.

In another European study, the fruits of several plants stimulated egg-laying by SWD females, but did not support full larval development and successful adult emergence. If these lab reports are supported by future field studies, such plants might be a useful component of an integrated control strategy as trap plants or so-called ‘dead-end’ hosts. For such an approach to be successful, however, the fruits must either be significantly more attractive than the crop being protected, or be present either earlier or later than the fruits of the target crop.

ii. Interactions with yeast

Once mated, adult female spotted wing drosophila respond strongly to odors produced by wild yeast species associated with fruit. These yeast odors are used as feeding cues, and may form the basis for developing an “attract-and-kill” strategy: in recent research, exposing flies to a mixture of yeast and insecticide reduced egg-laying and increased the mortality of adult flies compared to insecticide treatments alone. However, related work has shown that the effect is dependent on both the insecticide used, and the species of yeast. In some cases, there was no additional benefit from adding yeast to an insecticide spray that was also supplemented with cane sugar.

A rather more advanced approach to exploiting the attraction of SWD to yeasts involves the use of a genetically modified yeast strain to disrupt the expression and regulation of some of the pest’s critical genes by interfering with the normal functioning of its ribonucleic acid (RNA). Such ‘RNA interference’ techniques (RNAi) are being developed for many important crop pests. Recent lab-based research in California involved feeding a genetically modified yeast strain to adult spotted wing drosophila and recording mortality, activity and post-treatment egg-production: while there was no increase in fly mortality as a result of the treatment, the flies were less active and laid fewer eggs, prompting speculation that further refinements of the technique might have a future role in pest management.

iii. Environmental factors

Previous research has shown that SWD trap catches decline when humidity is low. Several research groups are now investigating whether different pruning and irrigation practices can reduce within-crop temperature and humidity and hence slow the rate of SWD population increase. Other research groups are comparing the survival of SWD in blueberry plantings with or without black plastic weed mats: the higher temperatures associated with the mats may reduce the survival of pupae in infested fruit that falls to the ground.

iv. Biological control

Various research groups in both North America and Europe have addressed the possible impact on spotted wing drosophila of both native natural enemies and a range of commercially available predators, parasitic nematodes and fungal pathogens. However, many of the studies have been conducted only under laboratory conditions and the results have been rather variable.

Two species of parasitic wasps (parasitoids) (Trichopria drosophilae and Pachycrepoideus vindemiae) have been found attacking SWD pupae in both the USA and Europe, as well as in the pest’s native range (various parts of Asia, including Japan and Korea). Trichopria drosophilae has a narrower host range than P. vindemiae and may have potential for mass-rearing for use in augmentative release programs. Additional parasitoids collected from South Korea are currently undergoing evaluation under quarantine in California, but it will be some time before such tests are completed.

v. Chemical control

At present, commercial producers rely heavily on season-long applications of a rather limited range of insecticides for spotted wing drosophila. With a pest such as this, with rapid rates of development and multiple generations per year, the risk of selecting for insecticide resistance is high. This is particularly true for enclosed tunnel systems (because of limited fly movement) and in organic plantings, where there are few effective chemical control options. There is already some evidence of reduced susceptibility to spinosad (Entrust®) in some organically managed berries in the western US. On the other hand, a recent study in Canada showed no increase in resistance to malathion in a laboratory population of SWD exposed to sub-lethal concentrations for 30 generations. Baseline monitoring for resistance to the most widely used insecticides is currently being conducted in fruit-producing regions in various parts of the US. Such monitoring will provide a valuable early-warning system if and when resistance develops.

In the meantime, a recent report from Georgia on the efficacy of insecticides used for SWD in blueberries showed that the adjuvant Nu Film P had some effect on prolonging the activity of spinetoram and spinosad after a simulated rainfall equivalent to 0.5″, and of malathion after a rainfall of approx. 1″. Nu Film P is listed by the Organic Materials Review Institute (OMRI) as suitable for use in organic production.

Future prospects

In conclusion, the heavy investment in research on spotted wing drosophila is now starting to produce results that at the very least will provide some additional management tools, and which in future may form the basis of a multi-tactic, integrated approach to the management of this pest.

This article was contributed by Tess Grasswitz, Extension Associate, Lake Ontario Fruit Program, Cornell Cooperative Extension. Originally published in Fruit Notes, Vol 16, Issue 18, August 18, 2016.

Steuben County first & sustained catch

Two male SWD were caught in Steuben County on August 13, 2016 in a trap set within a small planting of raspberry and blueberry; no SWD were caught in the trap outside the planting. The following week, sustained catch occurred with 5 male SWD caught within the planting and 2 male SWD caught in the trap outside the planting. These traps are being monitored by Stephanie Mehlenbacher, association community educator, Steuben County Cornell Cooperative Extension.

This report completes SWD early season monitoring. All New York monitoring sites have caught SWD. Maintain an effective SWD management strategy on late season berry crops.

2016 Drought Survey – NY & Northeast

Got drought issues on your farm? Help us collect regional information on the 2016 drought so we can help you be better prepared in the future. Fill out the 2016 Drought Survey.

This summer we have experienced a period of lower than average rainfall combined with higher than average temperatures that has led to a drought of moderate to unprecedented severity in New York and much of the Northeast. Learn more about monthly precipitation and this year’s drought on the Northeast Regional Climate Center, on You’re NEWA, and on Cornell Climate Change. “There is no unique climate change signature to this drought.  It is largely an unlucky sequence of events…

A 2016 drought survey is being conducted and we need your input. The survey is online, has 15 questions and should take only 5-15 minutes to complete. If your crops and irrigation water have been affected by this year’s drought, please help us help you by filling out the survey. Please go to the following link:  https://cornell.qualtrics.com/jfe/form/SV_9FDNwygyIV07kXP to access and complete the survey.

At this critical time, the survey seeks information on regional impacts and how you are coping with this situation. Our goal is for growers and those institutions and industries that support growers to be better prepared for drought in the future.  If your farm is affected by the current drought, but you are outside of New York State, please include the state in your answer to question 1. Where is your farm located (nearest town, and county(ies))?

This research is being conducted by NatureNet Science Postdoctoral Fellow Shannan Sweet and Professor David Wolfe as part of their larger project on New York State water resources and agriculture.

Thanks for your help!

Questions or comments? Contact: Shannan Sweet (sks289@cornell.edu; 607-255-8641) or David Wolfe (dww5@cornell.edu; 607-255-7888)

For more details on the 2016 drought see: http://climatechange.cornell.edu/drought-takes-its-toll/


This post was contributed by Shannan Sweet, Postdoctoral Fellow, Horticulture Section of the School of Integrative Plant Science, Cornell University, sks289@cornell.edu.

Clinton County sustained catch

Four male SWD were caught in traps set in a summer raspberry planting in Clinton County in the week ending July 11, 2016, indicating sustained catch. The following week, high numbers of SWD were caught and enumerated on July 19, 2016—10 male and 15 female SWD in the raspberries.

Traps set in the blueberries at this same location only had 2 female SWD in traps checked on July 19. A similar scenario was seen on another farm in New York where raspberry and blueberry are both grown. This would suggest that raspberry is more attractive to SWD and that traps set in raspberry may provide earlier warning of SWD arrival. This also suggests that raspberry is at higher risk of SWD infestation than blueberry.

Traps at this Clinton County location are being monitored by Lauren Fessler, summer intern, who is working with Amy Ivy, Extension Educator, Eastern NY Commercial Horticulture Program and Clinton County Cornell Cooperative Extension.

Essex County first catch

First trap catch in Essex County occurred on July 18, 2016 with a very large number of SWD caught in a summer raspberry planting. A total of 49 SWD, 33 male and 16 female, were enumerated in the four traps by Lauren Fessler, summer intern, who is working with Amy Ivy, Extension Educator, Eastern NY Commercial Horticulture Program and Clinton County Cornell Cooperative Extension. It is likely that sustained trap catch has occurred at this location by now.

Onondaga County sustained catch

A large number of SWD were caught during the week preceding August 3, 2016—53 females and 18 males—in traps set in a blueberry planting in Onondaga County. Luckily blueberry harvest at this location is winding down, because SWD populations are building up! These traps are being monitored by Nicole Mattoon, Field Technician, and Juliet Carroll, Fruit IPM Coordinator, NYS IPM Program.

Four female SWD, as seen through a dissecting microscope, that were caught in a Scentry trap. The inset in the middle is a close-up of the females ovipositor.

Four female SWD, as seen through a dissecting microscope, that were caught in a Scentry trap. The inset in the middle is a close-up of a female’s ovipositor.

Seneca County first and sustained catch

On July 20, 2016 first catch of 7 female SWD was found in a blueberry planting in Seneca County. The following week SWD had been caught again in the traps, indicating sustained catch. Traps at this location are being monitored by Gabrielle Brind’Amour, technician with Greg Loeb’s small fruit entomology program, NYSAES, Cornell University, Geneva, NY.

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