Spotted Wing Drosophila is a mouthful sometimes both literally and figurately. I usually can’t say it right so people like me will refer to them as SWD. In this article we will explain what Spotted Wing Drosophila are, why you don’t want them in your berry patch, how to identify them, and how to control them without using harmful chemicals.
What is the spotted wing drosophila?
Spotted wing drosophila or SWD came on the scene in the United States about 15 years ago. It is a small vinegar fly, about 2-3 mm in length, that originated in Asia. Spotted wing drosophila is a vinegar fly which most vinegar flies normally go for over damaged or super ripe fruit, but SWD lay their eggs in healthy fruit.
SWD does the most damage to fruit and berry crops with thin skin and are now found in the Northeast and most of the US. Their lifecycle goes from egg to adult in as little as 10-35 days depending on temperature. Only the male spotted wing drosophila have a spot on their wings. Females have a serrated ovipositor that they use to pierce the skin of intact fruit and lay their eggs inside the fruit.
Why you don’t want Spotted Wing Drosophila in your Berry Patch?
Female SWD inject 1-3 eggs per cut into the intact fruit or berry. Once the female spotted wing drosophila lays its eggs inside the fruit eggs can hatch within 1-3 days. Eggs hatch inside the fruit, where the larvae then feeds on the inside of the fruit or berry.
Home growers and commercial farmers alike are concerned with SWD because often times SWD isn’t caught until the larvae are eating its way through the berry harvest. Obviously once you reach this state berries aren’t saleable anymore and whole crops can be lost.
Yes spotted wing drosophila is a problem, even home growers don’t want to eat bugs in their berry crops. Keep reading because sometimes the answer is as easy as finding out who or what does want to eat insects and berries all day?
How to Identify Spotted Wing Drosophila?
It is easy to miss the subtle signs of an initial SWD infestation. The wound on the fruit is hard to notice at first, SWD injection sites are only the size of a pin prick. Once spotted wing drosophila has laid their eggs its usually too late to stop it entirely for the season. Within a few days larvae inside the fruit are feeding on your fruit and it is hard to detect unless you are looking for it.
A few days later SWD damage becomes more noticeable. The telltale signs of SWD damage is fruit that is shriveled, wrinkled, discolored, shrunken, and could be starting to rot. If you notice this on your fruit, it’s time to break open some berries and look for spotted wing drosophila larvae. SWD larvae at this point are mostly white and visible to the naked eye.
How to control SWD without using chemicals?
Controlling spotted wing drosophila is critical for all of us who grow berry crops. Some will say these techniques are most applicable for the backyard grower, the homesteader, or the small farmer but really any scale grower can use these SWD management practices.
Clean Harvest
The first way to control SWD is sanitation. This includes picking fruit as soon as it is ripe. Ripe berries attract SWD so increasing picking frequency can help control your problem. Rotten, damaged, overripe, and infected fruit should be collected and removed.
Keep it Cold
Picked fruit can be chilled to slow the growth of SWD larvae development. Freezing or canning your harvest will stop the larvae from developing further. If berries are for fresh consumption cool fruits to 35 degrees Fahrenheit immediately after harvest. Chill for at least 3 days. This has been shown to kill SWD larvae and preserve the marketability of your crop.
Let the light in
Next method of control is to allow more light to reach all parts of your berry plants by pruning. Spotted Wing Drosophila are sensitive to drying out and high temperatures. By pruning you allow more sunlight to reach the entire plant, this will encourage any SWD to find a more desirable home.
Choose Wisely
Another method to battle SWD requires some forethought. Before you have even purchased your plants do your research. Choosing early ripening varieties may give you a leg up on spotted wing drosophila. Combine that with thick skinned fruit and you can lower your susceptibility to SWD.
The Problem is the Solution
Lastly, one of my favorite ways to combat spotted wing drosophila is to use livestock to manage SWD for you. Timed right animals like chickens, ducks, geese, guineas and even pigs can help clean up your berry patch and orchard for you. In this video you see our chickens in the blueberry patch scraping and pecking for their next meal. Given a few days a flock of chickens like this will get every dropped berry. They will scratch through the top layer of soil and eat seeds, insect larvae, and hopefully any overwintering SWD pupae.
For the last several seasons we have sent my chickens into the berry patches for cleanup mode. How long to keep your birds in the berry patch will depend on the size your flock and the size of your berry patch. We have had success with letting them stay for 1-2 weeks. This is enough time for the chickens to get most SWD pupae trying to overwinter in the soil but not too much time where they damage our berry bushes. Your timing may vary so monitoring the flock is key to success here.
After the first year of implementing a combination of most of these control methods, I have noticed very little SWD in our berry patches. For us the keys have been harvested more often, keeping our plants pruned properly and using chickens has been part of our integrated pest management style. Our results have spoken for themselves in fruit quality and very little SWD losses.
Yes, implementing these types of controls usually takes a little more time and management than using chemicals but we really see the benefits. Afterall if we wanted to eat chemical laden fruit, we can find that on the grocery store shelf. If you have any questions about spotted wing drosophila or any other pests send them over and we will be happy to help you out!