Research in raspberries at Cornell AgriTech over the last four years has shown promise as an alternative tactic to reduce the impact of SWD on berries. As described in a previous blog posted in 2014, Hummingbirds, these birds may indeed enjoy eating SWD.
Preliminary data analysis for 2018 shows that when SWD numbers are very low or very high, there is little to no difference in the number of SWD caught in Scentry traps placed in the area of the field with hummingbird feeders compared to those in the area of the field without feeders. However, when numbers are moderate, there was a difference. Along a transect down the length of the field, the trend was for there to be fewer SWD in the hummingbird feeder area compared to the no-feeder area, as shown in the chart.
The diet of an average hummingbird consists mostly of flower nectar and insects. Flower nectar provides sugar to support their high metabolic rate… even higher during flight due to their rapid wing flapping rates. The insects hummingbirds eat provide them with protein, amino acids, and necessary vitamins and minerals. The insects must be small enough to swallow whole during flight — watch out, SWD!
Two grower demonstrations were undertaken this year, as well. One in blueberry and one in raspberry. Both growers undertook cleaning the feeders and changing the sugar solution twice per week to keep the hummingbirds well fed and active within their plantings. At the workshop held in Salem, NY last month, several of the tiny birds were seen dashing about.
Placing and maintaining 25 hummingbird feeders per acre, may be a bit too arduous for some growers. This is the number of feeders we've been using in our research and grower demonstration plots and the number used by the blackberry grower in Mississippi.
Other ways to attract hummingbirds to your berry planting that don't rely on the use of feeders, would involve allocating space for flowering plants that they prefer. Interplanting with rows of Monarda (bee balm), for instance, would be one approach.
Of course, SWD is around a lot longer than hummingbirds, which have, at this point in time, likely flown off to the South on their journey to the Yucatan peninsula in Central America. Flying across the Gulf of Mexico or along Mexico's coast, they make their way to their overwintering grounds. And, as SWD populations explode in late summer, it is difficult to control SWD, let alone rely on a flying predator.
If you think hummingbirds don't eat small insects, then guess again! I've seen these contraptions showing up in stores this year — to feed hummingbirds. They are rearing capsules for fruit flies (vinegar flies, as entomologists call them). Perhaps someone should tell them we don't need more SWD? ...just more hummingbirds!
Effective use of salt flotation will help you determine if your fruit are infested with SWD and if your spray program is working. It also will give you a perspective on what your customers may find when they take the fruit home to eat fresh or to make pies, jellies, jams and preserves.
I learned that variations on the salt flotation method helped a couple NY blueberry growers decide when to close this season. After a bad 2017 SWD season, when many NY blueberry growers suffered significant crop loss and shut down early, it was time to take action to monitor their fruit. Here are their methods.
We analyze a batch of berries picked off bushes and a batch gathered that have fallen to the ground. Blueberries are collected randomly across our 5-acre patch. We test batches of 20-30 berries from these two sources separately and then compare.
Mix a solution of one gallon of water to one cup of salt. Place collected blueberries in two separate, labeled bags. Slightly squeeze the berries to help release larvae. Some say to give it about an hour, but in most cases, if larvae are present, they will show up in the solution as early as 15 minutes. Of course, you will want to use a magnifying device such as a jewelers loop or magnifying glass. You will see small white larvae if infestation is present.
Their results this year:
Aug 08: negative, both from bushes and on the ground.
Aug 10: negative, both from bushes and on the ground.
Aug 11: positive, both from bushes and ground, but more pronounced with the latter.
In 2017, at least once, fruit tested positive for berries that were on the ground, but negative when picked from the bush.
The salt flotation method we use is basically the same as the method demonstrated at the SWD workshops in 2014-2015. But instead of pouring the salt solution into a low tray and visualizing larvae over a black paper with a hand lens, we pour the solution through a very fine stainless steel mesh permanent coffee filter and check for larvae under a dissecting microscope. It's faster overall, and much easier to find the hard-to-see 1st instar larvae (probably to my detriment, since in the past I could ignore what I couldn't see).
We collect 100 berries randomly from throughout the planting. These are covered with salt solution (1 cup salt in 1 gal water) in a plastic bag. I don't bother pressing on the berries to crack the skins as they suggest, but gave them plenty of time to exit on their own (at least an hour, usually 2 or more).
Results this year, percent fruit with larvae, in our unsprayed blueberry planting:
Jul 26: 1.5%
Aug 3: 4%
Aug 9: 16.5%
Aug 11: 30%
Aug 13: 78% - in two days, the SWD numbers rose dramatically!
In all cases, collect what appears to be sound, perfect fruit to test for SWD infestation using salt flotation. SWD entrance and exit holes in fruit are less than half a mm in diameter and practically invisible.
I hope these two growers’ experiences using salt flotation will motivate you to monitor your fruit in this way to check for SWD infestation.
There are still a lot of delicious berries out there; lets check them and protect them from this nasty insect!
A national team of researchers lead by the University of Georgia has released a new guide to organic management of SWD this May, 2018, Management Recommendations for SWD in Organic Berry Crops. The guide details information on non-chemical and insecticide approaches to protect berry crops against SWD.
Controlling SWD is particularly challenging, requiring a rigorous, persistent and diverse management plan. The guide details several management recommendations and suggests using as many control techniques as possible to reduce SWD infestation.
Funding for the research was provided by the USDA National Institute of Food and Agriculture Organic Agriculture Research and Extension Initiative (OREI).
Download the guide in PDF form here, http://www.ipm.msu.edu/uploads/files/SWD/SWDOrganicBerryCrops.PDF.
This post was written be Peter Werts, EcoFruit, IPM Institute of North America, Inc.
Strawberry renovation is a critical, but often overlooked part of growing June bearing strawberries. This year, with SWD numbers climbing, it’s even more important to remove fruit leftover in the field as quickly as possible. Otherwise, this fruit can serve as a food and reproductive resource for SWD population growth.
The task that creates a lag in the renovation process is the 2,4-D application. Most growers want to apply this herbicide all at once, so early berries are forced to wait weeks for the late varieties to finish — and in the case of ‘Malwina’, growers could delay renovation for more than a month. This tactic leaves a continuous supply of unharvested, cull fruit that SWD can develop in. A further delay is due to 2,4-D needing to be taken up by the leaves — mowing is delayed for 5 days to allow the weeds to absorb the herbicide. Given this added delay from choosing 2,4-D, growers need to make sure the weed species in their field are vulnerable to 2,4-D. If not, don’t delay renovation to use an ineffective herbicide, choose an alternate herbicide, and mow the planting as soon as picking is finished.
Whenever possible, mow the variety as soon as harvest is done. Be aware that mowing a water- or heat-stressed field can result in poor re-growth. Therefore, make sure the plants are well watered prior to mowing. If temperatures are above 90 degrees and you cannot irrigate, mowing should be delayed. If irrigation is not possible, consider skipping the mowing — but still renovate by narrowing the rows and throwing some soil up over existing crowns.
When strawberry fields go out of the rotation, remove them from production as soon as possible by tilling and then seeding a cover crop or a late season vegetable. If you cannot till the field, then mow it close to the crown or cultivate aggressively to help crush and dry down the remaining berries. This will help destroy this resource and limit SWD population growth in the remnant fruit.
Renovation Process – Immediately after Harvest is Finished
1. Ensure the field has adequate soil moisture.
2. Apply 2,4-D if needed.
3. Wait 5 days after 2,4-D is applied to mow. If 2,4-D is not used, mow immediately after picking.
5. Narrow the rows, cultivate middles of wide rows. Throw ½” of soil over remaining crowns.
6. Apply pre-emergent herbicide (ie Sinbar – make sure to read labels as some varieties are sensitive).
Two female SWD were caught in one of two traps set in an Amelanchier hedgerow immediately adjacent to a June bearing strawberry field during the week ending June 25, 2018. The two other traps at this location are inside exclusion netting over a blueberry planting and caught zero SWD. These traps are being monitored by Laura McDermott, Eastern NY Commercial Horticulture Program, Cornell Cooperative Extension.
Strawberry harvest is winding down and there is concern about strawberry renovation practices and potential spillover of SWD into nearby fruit from cull strawberries. Blueberries, raspberries and cherries are ripening and harvests are beginning across New York. Population levels are still low and, so far, no sites are at sustained catch. In addition, few counties across New York have caught SWD — keep an eye on the NY distribution map, because things may change rapidly in the coming week.
It is time to plan your insecticide program for managing SWD. Take this time to determine what insecticides will best fit your overall management program and markets.
What has held back the trap catch this season?
SWD first catch occurred very early this year, but sustained and subsequent increases in trap catch didn't materialize. Environment may have played a roll — weather had intermittent heat waves in May, June was dry, and nights were cool. Last year's serious SWD infestations in blueberries and tart cherries may have made growers more vigilant and willing to invest in insecticide sprays early, keeping populations down.
Why does the SWD population explode?
You can do the math. Let's think optimum conditions for SWD development. A single female can lay around 350 eggs during her lifetime, about 15 per day. The egg to adult phase of the life cycle takes as little as 6 days. So, one female in one day can result in 15 more adults 6 days later, and, during those 6 days, she will have laid another 90 eggs. 6 days after that, those 90 eggs will all be adults. Half of the 105 adults will be females, capable of laying ~350 eggs during their lifetimes...that's 18,375 eggs. A typical life span for SWD is 3 to 9 weeks and there are estimated to be about 10 generations per year in the US, depending on climate.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 management—use a combination of tactics, choose IPM.