What is Spotted Wing Drosophila?
The fruit industry is being plagued by an invasive pest called the spotted wing drosophila (SWD) that originally hails from Asia. Unlike its fruit fly cousins, this vinegar fly targets healthy fruit rather than damaged or rotting fruit. It lays eggs just under the skin of the ripening fruit with an ovipositor, making it difficult to detect until the maggots have already ruined the flesh.
Fruits most susceptible to infestation and damage include: cherries, raspberries, blackberries, blueberries, peaches, elderberries, and day-neutral strawberries. Grapes may also be damaged. Late season fruit varieties are more susceptible due to the timing of SWD mating season.
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Since this pest was first detected in the continental US in 2008, SWD has caused significant loss in the soft fruit industry. Sour cherry and blueberry growers have reported 20% or more of their harvest lost to SWD damage.
What Control Methods Are In The Works?
Researchers are working on biological controls, integrated pest management practices, and new varieties that are less susceptible to damage. Early varieties of fruit are less likely to fall prey to SWD infestation because they ripen and are harvested before mating season of this pest begins, in late July or August. This article in The New Food Economy reports on an experimental sour cherry that shows promise for escaping SWD damage due to its early harvest. However, it could be years before a new variety is available for market, plus this only addresses one susceptible crop.
Other possible methods for combating the SWD include predatory insects under review for release into orchards. Read more about the research in these articles…Spotted Wing Drosophila – Overview of National Research Program and Biological Control of Spotted Wing Drosophila.
While the research offers promise, fruit growers need options for combating these pests now. Otherwise they must increase pesticide application, or run the risk of reduced harvests and loss of profit. Home fruit growers are also impacted negatively by this pest.
How to Control Spotted Wing Drosophila in Your Home Orchard
Because home fruit growers are typically using fruit themselves rather than selling it, they have options that may not be available to commercial growers. Also, home growers have much smaller orchards that can be planted with a more diverse selection of trees and crops, making them less desirable to pests that spread quickly in large mono culture plantings.
Monitor Your Orchard for Presence of SWD
Rather than increasing pesticide applications in anticipation of SWD infestations, set traps and sample ripening fruit for pest presence. If the flies are found in traps or fruit they are likely to damage crops, making treatment necessary.
To set traps, mix baking yeast with sugar and water and place in clear plastic bottles or cups with lids. Place a yellow sticky trap above yeast solution to trap more SWD flies. Hang traps in orchards and surrounding areas, prior to fruit ripening. Traps should be checked daily for adult SWD flies. For complete instructions on mixing and setting traps, read this article by The UGA Blueberry Blog. (Article also shares photographs of infected blueberries, information about the life cycle of the SWD, and information about sanitation around orchards to help prevent crop loss.)
If SWD adults are found in traps, you may be able to reduce infestation by setting additional traps, covering fruit trees or bushes with fine netting to form a barrier, or implement another method of control outlined below.
Sample ripening fruit for presence of larvae by picking and placing in a clear plastic bag with salt water (use 2 tsp of salt per cup of water). Allow to set for 15 minutes and check for small white maggots in the water.
Use Cultural Practices To Reduce Spread of SWD
Good sanitation and cultural practices help to prevent overwintering and spread of this nasty pest. Clean up all dropped fruit and infected fruit that may cling to trees. Fix leaky hoses and reduce irrigation so that surfaces of vegetation are allowed to dry between watering sessions. Harvest fruit more often, harvest all ripe fruit, and chill or freeze fruit immediately after harvest to slow growth of, or kill, any present eggs and maggots. Don’t spread pest eggs and maggots by transporting infected fruit to new areas. It might be best to make jams, jellies, baked goods, or other value added products if selling at farmers markets or sharing with family and friends.
Predators Help Reduce Pest Populations
Guinea fowl, chickens and other poultry may be free ranged in the home orchard to clean up rotten fruit, adult breeding pests, and overwintering pupae. Guinea fowl in particular are noted for their ability to hunt out and eat pests, while causing minimal damage to crops. Pupae of the SWD may be consumed by poultry scratching and pecking at the soil surface. Be sure to wash fruit thoroughly before consuming.
You may wish to fence poultry out of your orchard during ripening and harvest of fruit to reduce damage to crops. Allowing different species of poultry to free range in the orchard during spring, early summer, fall and over the winter will help reduce pest populations without sacrificing fruit.
Mulch that provides habitat for ants, spiders, and other predatory insects and arachnids may also provide control of the SWD in the home orchard. Wood chips, buckwheat, and black plastic work well.
In southern states lizards, such as the Anole, may help reduce populations of adult SWD flies. Toads may also be encouraged to take up residence in orchards.
Releasing praying mantises may also help control the adult pests. In their nymph stage, praying mantises consume fruit flies and are likely to find the SWD flies to be a good food source as well. Time the placement of egg cases for the beginning of SWD mating season and place new egg cases at intervals throughout the rest of the season.
According to another article (‘Could Predatory Flies Provide Early Season Control of Spotted Wing Drosophila in Red Raspberry?), predatory dung flies may reduce numbers of the SWD in home orchards if fresh manure is applied in surrounding areas. Be sure to avoid contamination of fruit.
Allowing habitat for beneficial insects along the edges of the orchard helps to increase predation of pests. Monitor wild fruits with yeast traps for presence of SWD. Wild fruits that attract SWD include raspberries, blackberries, bush honeysuckle, elderberry, wild grapes, poke berries, autumn olive, and other berries that ripen in late summer. Although they may provide a trap crop, do not allow infected fruit to drop SWD maggots to mature on the ground and then infect fruit crops. Eradicate wild fruits if necessary to reduce presence of pests.
Start Now To Reduce Problems Later
Start the season out right by taking aggressive action to prevent SWD problems during fruiting season. Plant early ripening fruits or varieties with thicker skin to avoid damage. Clean up debris and drain damp areas around your fruiting plants. Start a flock of free range poultry if you don’t already have one. Plant seeds to attract beneficial insects. Mulch your orchard with wood chips or black plastic, or plant buckwheat to provide habitat for predatory insects and spiders.
During the growing season, cut back bramble canes after the early crop is harvested. Sacrificing the late cop may be necessary for best prevention. Set yeast traps and check often. Contact your local Extension office to find out when spotted wind drosophila is expected to mature in your area.
Using a combination of methods may help you avoid heavy losses and harvest higher quality fruit. Be careful when using any pesticides to prevent losses to pollinator populations.
For information about spotted wing drosophila in the home garden, check out these articles…
How do I manage spotted wing drosophila in my home garden? Cornell University. Includes insecticides found to be useful for controlling SWD. (Information source)
“Worms” In Your Berries? There’s a New Pest in Town by Mike McGrath, Gardens Alive. Includes information about organic insecticides for controlling SWD. (Information source…not an affiliate link.)
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