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In the last week of July 2017, my program found up to 100 SWD in some of the SWD traps in our raspberry research plot in Geneva, NY. Without a doubt, pressure from SWD and fruit infestation levels will be increasing as the SWD population explodes.

Sampling cherries in 2016 in western NY to check for SWD. None was found, but in 2017 the situation was different.

In addition, fruit crops normally escaping infestation are reporting problems with SWD. Early blueberry varieties are at high risk and the later varieties will be even more prone to infestation. A tart cherry grower in the Lake Ontario region reports a load of fruit rejected by the processor due to SWD infestation.

When harvest dates are close to insecticide application dates, the available insecticides that can be used against SWD on berries or on tree fruit are few because of the needed days-to-harvest intervals. The heavy rains washing off applied materials creates a greater challenge to keeping fruit clean of infestation.

A mild winter; early arrival of SWD; warm, cloudy, rainy weather; abundant fruit; prolonged ripening windows — these likely have created a perfect storm for SWD in 2017. We continue to learn about this pest, what drives it, and what we can do about it. We thought summer raspberries, early blueberry varieties, tart cherries and sweet cherries weren't at high risk, perhaps we need to rethink this in light of this year's situation and be more vigilant in 2018 for conditions that favor SWD infestation in our early fruit crops.

Reports from blueberry growers have come in. SWD — caught in traps, found in fruit, and plantings shut down. One of these growers in the Southern Tier of NY, caught a single male in a trap on Sunday, July 23, 2017, and then,

"In a matter of 3 days my 4 traps exploded with SWD. A minimum of 3 females, the same for males, (in each trap). I have been spraying, but the weather is a problem."

For organic growers, managing SWD in blueberries this year will be nigh on impossible. It is essential to rotate insecticide active ingredients (ai), that is: not using the same active ingredient back-to-back, repeatedly. Entrust is the most efficacious organically-approved insecticide against SWD (ai spinosad), but it is essential to rotate with other ai's such as pyrethrin (Pyganic) or azadirachtin (AzaSol) or the biological Grandevo, which aren't as efficacious. The weather, with heavy and frequent rainfall, washes off the insecticides applied, making it necessary to reapply sooner.

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.

For no spray growers, the best approach will be to invest in exclusion netting for a long term solution to protecting the crop. Even early varieties of blueberries have been hit hard in locations where SWD was found early, whereas in prior years these varieties escaped infestation. This underlines the importance of monitoring in your local area, whether with the use of SWD traps or by sampling fruit using salt flotation to detect infestation. Sampling 100 fruit allows you to quickly get a rough estimate of the percent infestation level from the number of larvae detected in those (12 larvae found/100 fruit = 12% infestation).

There is no magic number or percent infested fruit at which a field should be shut down to pickers, for a u-pick or roadside market. Be proactive with customers and make sure they refrigerate or freeze fruit soon after purchase. However, for the processing market, there may be zero tolerance for SWD-infested fruit. And for some direct market growers when infested fruit is found that signals the time to shut down.

Examine your caneberry plantings for conditions that promote SWD infestation and take steps to eliminate them. Although we cannot change the weather, we can alter conditions in the planting to reduce the cool, dark, humid areas preferred by SWD. Pruning and training systems can help maintain an open canopy to increase sunlight and reduce humidity. This will make plantings less attractive to SWD, will reduce SWD activity, and will improve spray penetration and coverage.

Bumblebee pollinating pruned and trellised raspberry.

Pruning tactics for caneberries (raspberries and blackberries) have been developed to achieve excellent fruit yield and open the canopy. Knowing different pruning strategies will help you manage SWD. Added benefits include improved fruit color and flavor promoted by sunlight, easier picking by workers and customers, and easier weed management.

Caneberries (brambles) grown in the Northeast include red and black raspberries and blackberries, all are susceptible to SWD infestation. However, fruiting season differs among cultivars, which influences the risk of infestation.

 

  • Summer bearing varieties develop berries on floricanes that grow the prior year and overwinter. Fruit ripens and is harvested in early to mid-summer, prior to SWD population buildup, lowering the risk of infestation.
  • Fall bearing varieties develop berries on primocanes that grow, flower, and fruit in the same year. Fruit ripens and is harvested in late summer and early fall when SWD populations are high and risk of infestation is extreme.
  • Plants developing berries on floricanes and primocanes haven’t had floricanes removed after fall fruiting. Fruit ripens and is harvested from early to mid-summer on the floricanes and from late summer to early fall on the primocanes. The risk of SWD infestation will be low early in the harvest season and will increase as the summer progresses and the SWD population builds up.

Pruning suggestions for summer bearing varieties
Summer raspberries – maintain 4-5 healthy floricanes per foot of row.
Blackberries – maintain 3-4 healthy floricanes per foot of row.
Black raspberries – maintain 6-8 floricanes per hill.
Everbearing – maintain 4 primocanes and 4 floricanes per foot of row.

Floricanes should be held upright with a trellis to facilitate spray coverage and air circulation. Holding fruiting canes to the outside on a V-trellis will keep them to the outside of the growing primocanes and facilitate spray coverage and harvest.

Prune out the smallest primocanes beginning when they are 12 to 18 inches high to select and keep the biggest and best canes. Keep a few more than the suggested cane density per foot of row or per hill. Begin removing spent floricanes in July along with any late emerging primocanes. In November, laterals on black raspberry and blackberry primocanes can be cut back to 3 or 4 buds.

Pruning suggestions for fall bearing varieties
Maintain 4-6 primocanes per plant on a trellis.

Encourage early fruiting by placing row covers over the row after mowing in the spring. Remove the row covers when the primocanes are 18 inches tall. This will bring on flowering about two weeks early and help avoid or minimize SWD damage.


References

Nourse, N. 2015. Raspberry pruning timeline. Nourse News. Spring:2-3. http://noursefarms.com/resources/newsletters/spring_2015.pdf

Pritts, M. 2013. Horticultural strategies for living with SWD. New York Berry News 12(10):1-2. http://www.hort.cornell.edu/fruit/nybn/newslettpdfs/2013/nybn1210.pdf

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To protect crops from SWD infestation, once susceptible fruit is ripe and SWD is in your area, manage them aggressively. Using a combination of tactics is better than relying on one; and is the foundation of integrated pest management (IPM). Talk to your local Extension office about how to monitor for SWD, read Extension newsletters and alerts, and know your crops’ growth stages. When adult SWD are present on your farm AND fruit are ripening, it is time to protect fruit and reduce SWD population growth with insecticides, unless exclusion netting is in place.

Raspberries, blackberries, and blueberries are at high risk of SWD infestation. Fall-bearing and late maturing varieties are at far greater risk than early maturing ones, because SWD populations build exponentially to very high levels in late summer and early fall. June-bearing strawberries may escape injury, whereas late summer fruit or day-neutral varieties may suffer damage. Cherries, both tart and sweet, elderberries, peaches and plums are also susceptible, but harvests may occur before SWD populations buildup. Thin-skinned grapes can be infested directly, though cracked or damaged berries are more susceptible.

Female SWD can lay eggs directly into sound fruit. They prefer ripe fruit, but can lay eggs in fruit even as ripening begins. Therefore, keep an eye on fruit development in your fields. Egg laying activity is greater under conditions of low light, such as dawn and dusk or in dense plant canopies, weed-shaded areas in a planting, or parts of the planting shaded by adjacent woods or buildings. Adult SWD, in general, are most active during cool, humid times of the day. We have had significantly cool and moist weather this spring and first catch of SWD has occurred in a few areas in NY already.

Examine your plantings for conditions that promote SWD infestation and take steps to eliminate them. Although we cannot change the weather, we can alter conditions in the planting to reduce the cool, dark, humid areas preferred by SWD. Canopy, weed and irrigation management will make the environment less favorable. If your fruit planting lends itself to full enclosure, consider exclusion netting to keep SWD out.

  • Canopy - Pruning and training systems must maintain an open canopy to increase sunlight and reduce humidity. This will make plantings less attractive to SWD, will reduce SWD activity and will improve spray penetration and coverage. Added benefits include improved fruit color and flavor promoted by sunlight, easier picking by workers and customers, and easier weed management. Pruning tactics have been developed to achieve excellent fruit yield and open the canopy. I will detail these in a later blog. Although the best time to prune is over, knowing different strategies now will help you in the future.

    Fruit of tartarian honeysuckle, also considered an invasive plant in NY, can support SWD development.
  • Weeds - Mow row middles and field edges routinely to reduce preferred habitat for SWD within and around the planting. Eliminate weeds within rows to increase sunlight penetration into the canopy, reduce preferred habitat, and improve spray penetration into and deposition on the canopy.
  • Irrigation - Repair leaking drip lines and avoid overhead irrigation when possible. Allow the ground and mulch surface to dry before irrigating. Eliminate problem areas where water puddles are slow to dry out. Raised beds are essential for raspberry production to reduce Phytophthora root and crown rot and will also help maintain a dry environment under the planting.

As fruit begins to ripen, know if SWD has been found in your area. If you are monitoring SWD with your own traps, check them routinely. If feasible, check them daily. It is easier to sort through a small number of vinegar flies caught in traps to look for SWD than it is to sort through 40-400. Females usually arrive first, but males are soon to follow and often caught along with females.

If SWD is in your area and susceptible fruit is just about ripe, insecticide treatments could begin. This will be especially true in years when SWD arrives early, because SWD populations will build to high levels placing even summer-maturing fruits at risk, particularly when weather conditions are ideal for SWD activity—cloudy, cool, moist. When SWD populations are high, treatments should be applied every five to seven days and repeated in the event of rain. Choose the most effective insecticides with pre harvest intervals that work for your picking schedule. Rotate insecticides according to their modes of action to prevent the development of insecticide resistance. Insecticide sprays will kill or suppress SWD adults, thereby reducing egg laying and slowing population buildup.

  • Insecticides – Based on the Cornell Pest Management Guidelines for tree fruit, grapes and berry crops we’ve put together quick guides to the latest list of approved insecticides for use against SWD on berries and on tree fruit & grapes. Always read and follow the pesticide label instructions.
  • Resistance management – Insects treated with the same pesticide repeatedly may develop resistance to that pesticide’s mode of action. The Insecticide Resistance Action Committee (IRAC) has developed groupings for modes of action. When materials in one IRAC group are used exclusively over an entire growing season and over years, they are at high risk of becoming worthless as a control measure due to resistance development. Always rotate between IRAC groups, as described on the label.
  • Protecting pollinators – If your crop is flowering, that means there are pollinators visiting flowers. Therefore, spraying insecticides will place pollinators at risk of non-target exposure to insecticides, unless these materials are applied when pollinators aren’t active, such as during dawn or dusk, or when the crop is no longer flowering. This can be particularly challenging for raspberries and blackberries, which may have a long bloom period that spans fruit ripening. Organic-approved products with the active ingredients spinosad, azadirachtin, and pyrethrum are toxic to pollinators. No matter which insecticide you choose, always read the label and keep pollinators safe from insecticide exposure.

Regularly inspect fruit in the planting for symptoms and signs, paying close attention to fruit ripening in areas prone to SWD activity—near woods, shaded or wet areas—span a random transect of the planting. Sample ripe fruit and examine it microscopically for egg breathing tubes or check for larvae with salt flotation. Get infested fruit out of the planting so SWD populations don't have a chance to buildup.

Blackberry showing SWD infestation
Blackberries severely infested with SWD will hang limp, drip liquid, and dry out on the fruit cluster; inset shows a larva dissected from the blackberry fruit.
  • Symptoms - Fruit can be inspected for evidence of larval feeding. Small holes in berries where the eggs were laid may leak juice when the berry is gently squeezed; this is especially diagnostic on blueberry, cherry, and plum. Infested red raspberry fruit may leave a red juice stain on the berry receptacle when the fruit is picked. Fruit with small indents or bruises where the berry surface appears to have flattened or deflated may be damaged. Help with identifying symptoms is found in the fact sheet, Recognize Fruit Damage from Spotted Wing Drosophila (SWD), from Oregon State University.
  • Breathing tubes - Egg breathing tubes are two tiny, evanescent, white hairs attached to the egg laid just below the fruit skin. In blackberry, grape, blueberry and cherry it may be relatively easy, though tedious, to find these on fruit in which eggs have been laid, but magnification is essential. A 20x hand lens or loop or a dissecting microscope is needed, and patience. Examine the entire fruit surface. Fuzzy fruit, such as raspberry, are harder to examine because of the difficulty distinguishing breathing tubes from normal plant hairs. To confound the inspection, once eggs hatch, the breathing tubes fall off. You may be able to train your eye to see SWD egg breathing tubes.

    Checking fruit for larva with salt flotation at a NYSBGA-sponsored workshop.
  • Sample fruit - Salt flotation can be used effectively to keep records of infestation levels in your harvests. At least 100 fruit per block per harvest should be observed for infestation. Immerse fruit in a solution of 1 Tbsp. (14.8 cc) table salt per 1 cup (236.6 ml) water. The salt solution causes larvae to move out of fruit and float into the salt solution. Suggested methods were adapted for NY growers by Laura McDermott in Guidelines for Checking Fruit for SWD Larvae in the Field (pdf).
  • Sanitation - Excellent sanitation will reduce SWD populations. Fruit should be harvested frequently and completely to prevent the buildup of ripe and over-ripe fruit. Unmarketable fruit should be removed from the field and either frozen, "baked" in clear plastic bags placed in the sun, or disposed of in bags off-site. This will kill larvae, remove them from your crop, and prevent them from emerging as adults.
Beautiful, ripe raspberries without SWD, that's the goal of every berry grower these days! Including Dale Ila Riggs, The Berry Patch, Stephentown, NY.

Protect your harvests and customer base. Pick only the best and perhaps still slightly firm fruit to help them last longer in your markets. Chilling fruit after harvest is an essential step in prolonging shelf life. Picking crews can pick overripe or suspect fruit into a separate container to get them out of the field. Although the larvae of SWD are safe to eat, most people won’t want to do so. Informing customers about SWD and making sure they refrigerate fruit once home will help them understand how to deal with this invasive insect, and still benefit from eating nutritious and delicious fresh fruit.

  • Cool berries - Chilling berries immediately after harvest to 32° - 33° F will slow or stop the development of larvae and eggs inside the fruit. U-Pick customers should be encouraged to follow this strategy to improve fruit quality at home.
  • Proactive – Be proactive with your customers. Let them know that you are doing everything you can to manage SWD in your fruit crops. Inform them about refrigerating or freezing fruit as soon as they get home. Highest quality of preserves, jams and jellies will be achieved if prepared soon after purchase.

The take home message for SWD managementuse a combination of tactics, choose IPM.

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.

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.

The earliest ever arrival in New York State of this fast-reproducing insect rang alarm bells in anticipation of heavy infestations in early or mid-season berry crops that often escape damage. However, larval infestations have been curiously low in summer raspberry and blueberry crops sampled in many areas, including the Finger Lakes region. We suspect that the hot, dry conditions we have been experiencing could explain these low infestations.

Breathing tubes of SWD eggs as seen, magnified by a microscope, on the surface of blackberry fruit.
Breathing tubes of SWD eggs as seen, magnified by a microscope, on the surface of blackberry fruit.

Small flies like SWD are sensitive to desiccation (drying out) and therefore prefer to lay their eggs in darker, more humid conditions. SWD are more likely to lay eggs in shaded fruit, lower in the plant canopy, and even prefer laying eggs during the cooler, low-light conditions of dusk over other times of the day.

A halt in egg laying is reported in California when conditions are dry and temperatures climb above 85-90°F. A recent study conducted by our colleagues in Oregon has found that humidity not only plays a positive role in egg laying behavior, but also in the number of mature eggs carried by female SWD. (Tochen et al. 2016. Humidity affects populations of Drosophila suzukii (Diptera: Drosophilidae) in blueberry. J. Appl. Entomol. 47-57.) In other words, a female exposed to more humid conditions will make a greater investment of resources to grow new eggs and she will choose to lay more of those eggs.

This sensitivity to hot, dry conditions may explain the curiously low infestation rates we’ve seen so far in 2016, given the high daily temperatures and drought conditions. And, there are significant implications for management. Plant canopy management may be an important cultural strategy for SWD control. In addition to improving fruit quality, proper pruning can open up plant canopies. An open canopy aids in better spray coverage when applying foliar insecticides and also helps in decreasing the humidity within the microclimate of that canopy. There are ongoing studies taking a direct look at the effects of pruning and humidity on SWD infestations, so stay tuned for more information in the future.

This post was contributed by Dr. Anna Wallingford, postdoctoral research associate, in Dr. Greg Loeb's small fruit and grape entomology program, Cornell University, NYSAES, Geneva, NY.

Figuring out which SWD trap and lure works best has been an ongoing project for many in the Northeast and across the US and Canada. Below are summarized results from Rich Cowles, Connecticut Agricultural Experiment Station, Greg Loeb, Cornell University, and researchers at the University of Guelph, Ontario, Canada.

From Greg Loeb

In 2015 trials in NY, we compared the commercial Sentry lure and the commercial Trece lure with our fermenting whole wheat dough. For the trial conducted in June and July, where monitoring matters most before SWD populations build, the Scentry was best in terms of number of SWD captured but statistically about the same as the whole wheat dough lure. Scentry and whole wheat lures were also good at capturing SWD before we detected fruit infestation. Scentry was more selective, catching fewer non-target drosophila and fewer other insects.

In 2015, the Trece manufacturer had problems with release rate on their SWD lures that were made early in the year. We tested both Trece and Scenery later in the season (August), using a different Trece lure release design and the two were similar.

For 2016, we are recommending Scentry but will be testing the latest Trece design in June to see if our results from August stand up.

From Rich Cowles

In 2013, tests found the our actively fermenting whole wheat dough lure was clearly superior to the commercially available Trece lure.

In 2014, there were some “tweaks” with the Trece lure and it was the best performing lure, but it has to be used over apple cider vinegar drowning solution (ACV). The Suzukii Trap bait was rated second to the Trece + ACV, and the two were statistically equivalent. The kombucha lure was rated third in that trial, but variation in fermentation of the kombucha probably decreased its ranking.

In 2015, with better kombucha production, the Suzukii Trap and kombucha were neck and neck in performance, and so I think we can expect all three of these baits will perform well and be equivalent for 2016. Both the Trece lure and the Suzukii Trap lure catch fewer unwanted species than the kombucha. Extensive tests of the Suzukii Trap lure have found it highly consistent and more selective for trapping SWD and African fig fly, rather than the other Drosophilid species. The Suzukii Trap lure also tends to capture a somewhat higher ratio of female SWD, so care must be taken to look for female as well as male flies in first detections.

Suzukii Trap, manufactured by BioIberica, is about to be launched to the US market. The Suzukii lure comes in 5-liter jugs. An advantage with the Suzukii Trap lure is that the liquid does not spoil, and can be reused over several weeks. When using this bait you can filter flies when servicing traps with a fine metal mesh coffee filter, and save the lure solution for reuse. The volume that evaporates can be replenished with fresh bait. BioIberica SWD traps are not being marketed in the US. If you use the Suzukii Trap lure you can use (1) a cup trap, but it may not efficiently retain flies, or (2) a modified McPhail trap, which is characterized by having a donut-shaped reservoir for a liquid lure. Flies enter the trap from underneath, by flying through the donut hole. Once inside such a trap, flies rarely leave, because the top of the trap is transparent and flies try to fly upwards to attempt escape. I have designed a modified McPhail trap from a 2-liter soda bottle. When constructing the trap from soda bottles use a small head space volume to greatly enhance trap capture. Instructions for making these traps can be found at: How to Trap Spotted Wing Drosophila, http://www.northeastipm.org/about-us/publications/ipm-insights/how-to-trap-spotted-wing-drosophila/

From University of Guelph

Andrew Frewin, Justin Renkema, Hannah Fraser, and Rebecca Hallett conducted research on ACV, yeast plus sugar water, the commercial Pherocon SWD dual lure, the commercial Suzukii Trap, and the commercial Scentry lure.

They concluded that, on the basis of early SWD capture and fewer non-target captures, the Scentry lure performed best. They are recommending this lure for Ontario in 2016. The Pherocon results were affected by loss of the early weeks' samples and tests need to be repeated. And the ACV and yeast plus sugar water performed poorly compared to the commercial products and are not recommended.

Post content contributed by Mary Concklin, Fruit Production and IPM Extension Educator, University of Connecticut.

The Sustainable Spotted Wing Drosophila (SWD) Management for US Fruit Crops project, funded by NIFA, needs your help. This five-year project is developing national research and extension approaches to minimize the impacts of SWD. They include:

  • new management tactics and programs
  • expanded pesticide registrations for SWD
  • information and training on SWD for growers, extension agents, and others

In order to achieve this and ensure that the research and extension efforts match the needs of growers, the project is collecting information on the impacts of SWD on berry and small fruit growers' farms, your current management practices and preferences, and your needs for better management of SWD.

Participation in the survey is voluntary. The survey doesn't collect personally identifying information and the data will only be analyzed and reported in aggregate form. Please help us help you by providing your perspectives on SWD in the survey.


Access the SWD survey at this link:

Sustainable SWD Management Survey https://survey.ncsu.edu/swd/


Thank you!

 

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The SWD monitoring network Counties are all positive for SWD as of last week, August 28, 2015. A lot of SWD are being caught in traps in research sites now with population numbers expected to climb into the thousands before frost knocks them back and forces them into winter diapause.

All sites in NY's SWD monitoring network reported SWD by the end of August. Counties in white did not have traps reporting to the network.
All sites in NY's SWD monitoring network reported SWD by the end of August. Counties in white did not have traps reporting to the network.

Reports are coming in of severely infested fall raspberries. This fall will be especially challenging for fall harvest of susceptible fruits. Blackberries and raspberries are particularly vulnerable and will require intensive management with sanitation and insecticide protection. One sanitation strategy used in California for berries is for workers to crush any fruit that has fallen to the ground, reducing the chance of larvae surviving to grow into egg-laying adults. For insecticides, maintaining good coverage is essential, so keep track of rain events that can wash off insecticide (>0.5 inch) and reapply at the appropriate interval listed on the labels.

Late-season blueberries, peaches, plums and grapes are vulnerable to infestation, though not as susceptible as brambles, it will be wise to examine the crop for infestation. Fruit that is softer than it should be, with dull sunken areas and tiny drops of sap may be infested. Hold marketable fruit samples on white paper towels for a day or so and rotate it to see if it is leaking from tiny pinholes indicative of larval breathing sites. Use salt floatation to float out larvae and assess the relative abundance of larval infestation and severity of the problem. Place 50 ripe, marketable fruit in a plastic bag, cover with salt solution (1 Tbsp salt/cup water) and examine in 15-30 minutes for emerging larvae. Larvae are small 1-3 mm or 1/16-2/16 inch long. More on checking fruit for infestation is in the blog Do my fruit have SWD?

SWDlifecycleInfestations can contribute to sour rot in grapes and fruit decays in other fruit crops. Severely infested raspberries will appear to melt off the plants.

If fruit is still ripening and ripe fruit is infested, clean pick all ripe and overripe fruit and discard it to remove the developing SWD population from the planting. After clean picking and sanitation, apply an effective insecticide to protect the ripening fruit.

Discard infested fruit in clear plastic bags held in the sun to solarize and kill larvae or freeze it. Holding culled fruit in tightly closed plastic bags will prevent SWD adults to emerge from the infested fruit into the environment.

High temperature will dissuade SWD, but hot days this past week in NY have been followed by cool nights which has likely allowed SWD adults to escape the impact of the heat. High humidity is conducive to SWD development, so that factor will also weigh in to make management difficult this fall. The microclimate in the fruit planting can be altered with pruning practices, so plan now to prune for a more open plant canopy in 2016.

Consult the resources in the right hand side bar for more information on SWD.

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