Do you know the fruit flies that hover and look you in the face when you have too ripe fruit? Those who use scientists as model systems to advance medicine?
They are very annoying, but they don’t do much harm. The common fruit fly (Drosophila melanogaster) only lays eggs on fruits that are already damaged or overripe.
The spotted wing Drosophila (SWD) is NOT such a fruit fly. It is a fruit killing machine. The female even has a special egg-laying organ that is serrated like a saw so that it can lay its eggs in ripening fruit.
This makes the SWD a threat to a variety of soft-skinned fruits, from cherries to peaches. This fly is a particular threat to raspberries and blackberries and can completely destroy a harvest in the late season.
This insect is fairly new to mainland America and was first sighted in California in 2009. However, it didn’t take long for it to spread to most of the United States, Canada, and Mexico.
The SWD is the most studied berry pest in the United States.
Controlling this fruit fly is difficult, but not impossible, and we at Gardener & # 39; s Path will provide information on organic techniques that have been used successfully to protect berries and other fruits from the spotted wing Drosophila.
Identification, biology and life cycle
The spotted wing Drosophila (Drosophila suzukii) comes from East Asia and then established itself in Hawaii.
These fruit flies are approximately 1/10 inch long and have bright red eyes and black horizontal stripes on their belly. They live for 20-30 days.
The male SWD looks like a typical fruit fly, only that it has a striking black spot on the front edge of its wing. It’s the women who really look different.
Fruit flies lay their eggs with a long tube called the ovipositor. If you look under a magnifying glass, you can see that the ovipositor of a SWD has teeth – like a small saw. This enables her to lay her eggs in the fruit.
Within a day of laying the eggs, the white legless larvae hatch and start feeding on the fruit when the temperatures are between 43 and 89 ° F.
Under favorable conditions for the SWD, the fruits begin to collapse just two days after the eggs have been laid. Fruits like cherries show visible dents around the larvae.
This feeding makes the fruit susceptible to additional damage from other insects or mold.
The larvae live 5-7 days before pupating 4-15 days inside or outside the fruit.
The fruits usually fall to the ground when the flies begin to pupate. They can break apart when handled.
The SWD reproduce quickly and can produce at least 15 generations a year. It doesn’t help that a single woman can lay more than 300 eggs in her life!
In addition, the flies can complete their life cycle in just 10 days under ideal conditions.
As a result, their populations build up over the course of the season, making them a particular threat to berry fruits in the late season, such as blackberries, autumn raspberries, blueberries in the late season, and neutral strawberries.
The infestation begins when the fruits start to color and continue to ripen.
Preferred temperatures and conditions
The SWD live in warmer climates because the eggs and larvae cannot survive the freeze. Twenty-four hours at 28 ° F kill three quarters of adult flies, while temperatures of 91 ° F do the same.
The SWD live all year round in ideal temperate climates. This includes California, Florida, Oregon and Georgia.
In regions with cold winters, flies usually become active from mid-June to early July.
The SWD are most active at dawn and dusk when temperatures are between 59 and 70 ° F. Your preferred temperature is 68 ° F.
Unfortunately, these are the temperatures in early summer and fall in large parts of the country at the same time that the berries and other types of fruit ripen.
This makes them a particular threat, as flies can migrate between different types of fruit when they ripen at different times, so that many types of fruit can be affected during a single season.
Because the flies are so small, they dry out easily and prefer wet weather. This leads to behavior that makes them even more of a threat.
On hot days, they hike to the cool, damp canopies in the fruit trees. This brings them even closer to fruits that can infect them.
The SWD can infect many types of commonly grown fruits, including Raspberries, ElderberriesBlackberries Strawberries, Cherries (sweet and sour), BlueberriesPlums PeachesNectarines Apples, Pears and persimmons.
Grapes are not a preferred host, but the SWD attacks them if they are damaged by hail, birds or cracks in the fruit.
These flies can also live on an enormous number of wild fruit hosts. including berries, American pokeweed, bush honeysuckle, dogwood and sea buckthorn.
An extensive list of the SWD’s wild hosts in southern New England can be found on the website of the Fruit Resources page at Cornell University for the insect. Chris Maier of the Connecticut Agricultural Experiment Station compiled this list.
Harvest losses due to the spotted wing Drosophila
The combination of its broad host range of fruits, the fast generation time and the way in which it damages the fruits makes the spotted winged Drosophila an extremely serious pest.
The SWD can cost a fortune to producers and completely destroy late-season crops such as blueberries or autumn raspberries.
Harvest losses due to this pest have been recorded in the western United States alone were appreciated to reach up to $ 500 million a year.
The fact that the larvae live in the fruit protects them from insecticides and makes them even more difficult to control.
The SWD is difficult to control under all conditions, especially for organic farmers. However, it is not impossible.
For a long time, several large universities had focused on organic control methods for the SWD. The USDA Institute for Organic Research and Enlargement (OREI) of the National Institute of Food and Agriculture supplemented and published its efforts by funding a two-year study in which several universities participated to learn how to best combat this pest his results in 2017. The results are summarized by Dr. Andrew J. Petran.
Recognize with traps
While growers of many cultures use traps as an indicator of the level of infestation, the best use of traps for the SWD is to let you know when they first reach your property so you can take immediate action.
Another advantage of using a trap in this way is that you can wait to treat your plants until you are sure you have the SWD on your property.
You should monitor from the early stages of fruit development to the end of the harvest.
However, there is an immense variety of traps, from homemade sugar or vinegar traps to those you can buy.
The most common is a clear deli trap with holes in the side and liquid on the bottom that catches the flies.
An article by Dr. John P Roche from 2018 in Entomology Today checked the doctoral thesis of Dr. Danielle Kirkpatrick at Michigan State University on choosing the best type of trap for catching SWD.
Previous research had shown that red traps work better. This makes sense because the flies are attracted to red fruits like cherries and raspberries.
Dr. Kirkpatrick found that the flies were much more attracted to red balls and red plate traps baited with scentry baits (a special attractant for fruit flies). You can Buy red Scentry Delta traps from Arbico Organics.
Place a trap in the canopy in the shade or on the north side of the row. If your plants are near forests or river banks, set up another trap at the closest border to that area.
The edges are usually more affected than the interior. If you have multiple traps, your management may be able to focus on more affected areas.
Commercial baits usually last at least four weeks.
Make sure the holes in the trap are not blocked by vegetation so the SWD can easily fly in.
You should check the traps once a week. You may have a mix of different types of fruit flies, and some native fruit flies look superficial like the SWD.
Use a 10-30x magnifying glass to look for the serrated ovipositor of the SWD females. You can recognize the males by the distinctive dark spots on their wings.
When you identify the dreaded pest on your property, it’s time to take action. You should do this immediately because the populations can build up very quickly.
For example the detection of a fly in a conventional berry or cherry grove in Michigan can put producers in action immediately when their fruits ripen or are ripe.
Hygiene is extremely important to prevent the spread of the infestation. One of the first things you should do is check your fruit.
You can gently squeeze fruits like blueberries. When they are infected, juice seeps out.
Raspberries are too fragile for this treatment, but infested fruits can leave a red stain on the berry jar once you’ve picked the fruits.
Flattened fruit with small bruises or depressions can be damaged.
Club the infected fruits and remove them as soon as possible. There are several steps you can take to kill the larvae. You can freeze or bake the fruits by placing them in clear plastic bags in the sun for at least 48 hours.
Or you can dispose of it outside of the site. It is important to remove the fruits with larvae so that they do not show up and lay eggs as adults!
In the past, experts recommended burying the fruit. However, it turns out that the larvae can escape from the ground, so you should no longer practice this technique.
If you have help harvesting your fruit, you can give your helpers two buckets. One is for marketable fruits. The other is for damaged or overripe fruit to remove as many larvae from your garden or orchard as possible.
Spray an insecticide immediately unless the plants are blooming. You don’t want to kill the pollinators.
While there seem to be a number of organic insecticide options that you could use, research has shown that many of them are ineffective against the SWD.
Cornell University researchers, including Laura McDermott and colleagues, tested a number of insecticides that homeowners can buy that are labeled for use against these harmful flies.
Spinosad was by far the most effective and controlled the SWD on cherries, apricots, plums, peaches, nectarines and blueberries. It was also effective for raspberries, blackberries and loganberries.
A number of brands that contained Spinosad as an active ingredient were highly effective, including formulations of Bonide Captain Jacks Deadbug Brew available through Arbico Organics.
Spinosad for commercial producers
However, if you sell your berries, you are prohibited from using the Boninos Captain Jack formulations from Spinosad. You have to buy Entrust®instead.
Because of concerns about developing insecticide resistance, you need to switch to a different type of organic insecticide after two uses. Most of them don’t control the SWD as effectively as Spinosad.
Raspberry, blackberry and blueberry growers are limited to six applications per year, while strawberry growers can perform five applications. Stone fruit farmers are limited to three per year.
Heather Leach, Matthew J. Grieshop and Rufus Isaacs from Michigan State University reported that the insecticide Grandevo® worked well to control the SWD when rotated with Entrust®. Farmers across the country have observed some variability in the level of control with this pesticide.
Supplementing insecticides with disinfectants
Two disinfectants that are used in tank mixes or rotations with insecticides are promising for use in organic programs. Although they are registered as fungicides and not as insecticides, Jet-Ag is®and OxiDate®2.0 can improve the effectiveness of insecticides that are only classified as “fair” to control the SWD.
Ortho Bug B Gon Systemic Insect Killer Concentrate from Amazon
Acetamiprid provided good control against the SWD on apple, pear, grape or strawberry. This compound is available in a number of formulations made by Ortho, including Ortho Bug B Gon Systemic Insect Killer Concentrate and Ortho Flower Fruit & Vegetable Insect Killer Concentrate.
Ortho Flower Fruit & Vegetable Insect Killer concentrate on Amazon
One thing that could increase the effectiveness of the sprays is to add a small amount of cane sugar to the spray tank. Add 2 teaspoons per gallon of water.
You should spray early in the morning or late in the evening as this is when the SWD are most active. If you do this, your treatments will be more successful.
Manage the canopy and water consumption
Since the flies like cool and humid places, they are attracted to the inside of the canopies.
Prune your plants so that the canopy is open in elevated sunlight and reduced humidity. This has the added benefit of improving spray coverage. This strategy is particularly important for organic fruit production.
Also reduce moisture as much as possible. Repair broken irrigation lines and wait for the soil and mulch to dry before watering.
Let the berries cool immediately after harvesting
Place your fruit immediately at 34-36 F. This slows down or prevents larvae or eggs from developing in the fruit. If you cool the fruit for three days, the SWD will be killed.
If you have customers who pick their own berries, you should encourage them to do so at home. Nothing works as well as a sticker saying “Put me in the fridge.”
Use the network
If your plantings are small enough, you can enclose them in nets to exclude insects. Use a mesh with a mesh size of 1 millimeter.
The USDA OREI research team found that the use of nets “can be consistently effective” to reduce SWD infestation in small fruits such as raspberries, blackberries and blueberries.
The researchers also found that a net with a heavier net (80 gram insect net) was most effective in excluding the SWD from the cultures.
In addition, Heather Leach, Matthew J. Grieshop and Rufus Isaacs from Michigan State University noticed, that The combination of nets with organic insecticides reduced the SWD populations more effectively than using either strategy alone.
You can either enclose the entire system in the network or build a high tunnel and lay a network over the ventilation holes, entrances and exits.
One problem with this approach is that pollinators can be excluded. So if you have summer blooming raspberries in the net, you should store them Bumblebees or other pollinators to ensure that your plants are pollinated.
It is important that you install the network before the SWD becomes active. Failure to do so may result in worse infestation than if you did not use the network.
If you use high tunnels in a warm climate, you may need to use ventilation to prevent your plants from being damaged by overheating.
An additional advantage of using nets is that they can also protect against birds, some other types of insects, and certain rodents.
Mulch with plastic
Sometimes the larvae fall to the ground and pupate in the ground. You can interrupt this cycle by mulching with a black plastic weed barrier. Decreasing the survival of the SWD can reduce the likelihood that your fruit will be infected.
An additional advantage of the plastic barrier is that weeds can be removed and water can be retained.
Harvest your fruits frequentlyy
Ripe fruits serve as strong attractants for SWD. If you wait three days to harvest your fruits, they will likely build populations of the pest. Harvest every two days or even every day (especially with raspberries) to minimize the infestation of your plants.
Monitor your fruits regularly
You should look for infestations between sprays to see if the treatments work. It is possible that you have the larvae in your fruit before you have discovered adults in the traps. It is therefore important to monitor the fruit.
One way to do this is to randomly select 25 fruits from your garden and place them in a Ziploc bag. Make a solution of salt water with 1-2 teaspoons of salt per cup of water and put it in the bag.
Squeeze each fruit lightly and add to the solution for 15-30 minutes. Then you see if larvae swim in the water
If the larvae are small, you may need to use a magnifying glass. The easiest way to see them is to put a light behind the bag that shines on the larvae.
If not, you know that your fruits are not infected! If you find larvae, they may be from a different type of insect.
Another way to check your fruit is to look for the “stitches” – the tiny holes that the females made when they laid their eggs in the fruit.
Phenology management to avoid Drosophila with spotted wings
If you know the time of year the SWD is normally active in your region, you can grow plants early so that the fruit has already ripened when the flies materialize.
This approach is known as Phenology management.
Your local counseling center can provide charts showing when the pest is normally active in your area.
One example is a blueberry grower in southern Minnesota. If he or she plants an early-ripening variety like Bluecrop, Draper or Duke, the fruits ripen in early July – before the SWD begins to attack the plants in the region.
Some growers avoid autumn raspberries altogether and only focus on one summer harvest. Short-day strawberries that bear in June are less affected by SWD than day-neutral strawberries that ripen later in the season.
Another option is to choose fruit with a thicker skin, since the flies take longer to lay eggs in these types of fruit.
Organic techniques can triumph over the spotted wing Drosophila
The spotted wing Drosophila is very aggressive, productive, invasive and can completely destroy late berry fruits.
However, using an integrated Pest Management (IPM) approach, you can control this pest using organic techniques.
Monitoring fruit flies is an essential part of any control program, as you need to take action on your property immediately upon spotted Drosophila wing detection.