It seemed as if nothing could stop my prolific raspberry bushes from running their marathon harvest. And then the worms came.
I started noticing them a little here and there. No big deal, right? I’d just soak the raspberries in salty water and dump off the dead floaters. But then what began as a small nuisance suddenly became an unmanageable infestation.
Where were these worms coming from?!
My guess was that they had something to do with all of the tiny little gnats I’d noticed swarming around my bushes. See that fly on my raspberry there? Look closely, I’m working with a point and shoot camera here.
Turns out, I was right. Those teeny, almost translucently white worms are the larvae of fruit flies. The Spotted Wing Drosophila is one type of fruit fly which is becoming a particular problem.
What is the Spotted Wing Drosophila?
The spotted wing drosophila, also known simply as SWD, is a tiny fruit fly that first came here from Asia in 2008. Since then, it has spread pretty much all over the United States. It attacks all kinds of berries, including strawberries, blackberries, blueberries, stone fruits, and of course, raspberries.
SWD not only can ruin your fruit, as I found, but they also lead to an increased likelihood of infestation from other insects as well as to an increased threat for rot fungi, bacteria, and other diseases.
Spotted wing drosophila first appear in late June, or sometimes a little earlier or later, depending on your climate. Just one fly can produce up to 12 generations in a single year, with populations peaking toward the end of the summer.
Here’s how this menacing little pest operates.
The adult will lay eggs inside your fruit. When the small maggots appear (these are the worms I was telling you about!) They will eat the fruit before falling to the ground and pupating. Later, they’ll merge as adult flies. This cycle will then repeat itself, happening as fast as seven days in warm weather or up to 25 days when it’s cooler.
Lots of people don’t even realize that the SWD flies are there until the worms appear. Creepy!
What is the Difference Between SWD and Regular Fruit Flies?
The difference between the SWD and regular fruit flies, besides the tell-tale black spot on the male fly’s wings, is that while everyday fruit flies generally lay eggs in overripe or damaged fruit, Spotted Wing Drosophila have a more aggressive approach. They lay their eggs in the flesh of underripe fruit, making it hard to beat the bugs to the harvest. The eggs hatch, and those nasty little raspberry worms are soon to follow.
These pests are actually relatively new here, and are becoming a HUGE pain to berry growers across the US. Not only do they effect raspberries, but blackberries, blueberries, cherries and strawberries as well.
How to Prevent and Get Rid of Spotted Wing Drosophila Flies and Worms
Experts are still testing different methods of control, but there are a few preventative measures you can take to reduce the chances of an infestation:
Keep Plants Picked of Ripe Fruit
Ripening fruit will attract the Spotted Wing Drosophila, and will spread breeding grounds. Do not leave overripe berries on the vine, and do not let them fall to the ground as this will encourage an infestation.
Pick the vines clean, and do not compost unwanted berries. The heat from the compost is not high enough to kill the SWD larvae and they will reemerge the following year. I’ve been feeding my overripe berries to the chickens, but you can also seal them in a ziploc bag and leave it out in the sun to kill the worms. You must keep your plants picked clean of all ripe fruit every single day.
Destroy Infested Fruit
As much as I hate having to get rid of fresh fruit, unfortunately, you may just need to get rid of fruit that you know to be infected. There are ways to get the worms out of the berries, but it can take some time and some patience. Instead, just get rid of the fallen fruit or the infested fruit and put it in the plastic bags, as I mentioned above.
Remember, put the bags in the trash and do not compost them. A word to the wise – you also can’t bury infested berries or plant parts. These pests can survive being buried as deep as a foot and a half!
Keep Plants Pruned
Fruit flies like humid, shady environments. Thin ’em out and keep sprawling varieties trellised. Burn the prunings instead of composting them.
Do a Ground Clean-Up
SWD larvae can overwinter in the soil and reemerge the following year. It is recommended that you cultivate the soil around your plants to expose the larvae to the elements. They don’t survive well in very cold or hot temperatures. I’m going to go an extra step and sprinkle Diatomaceous Earth around my plants after I thin them out.
When you’re cultivating the soil, do so slowly and methodically. You will want to use a rake or otherwise shallowly cultivate the soil to expose the larvae to the sunlight.
This is somewhere else you can put the chickens to work, by the way – let them till the soil near the plants. They shouldn’t harm the plants, particularly if you already have them covered, but they can really do a number on the SWD.
You can put out a vinegar or yeast-sugar trap to lure these pesky flies. It won’t catch enough of them to help a bad infestation, but if you set the traps out when the fruits are just beginning to appear, you will be able to monitor the arrival of the flies.
Setting traps at the end of the season might also help reduce the population for the following year. Page 2 of this document explains how to make your own fruit fly traps.
Essentially, these traps are more or less the same ones you might use inside your home. You’ll have a combination of yeast, water, and sugar in a cup that ferments and attracts the flies. You’ll have to check it frequently so you know when the flies have arrived, but it’s a pretty effective way to keep these pests at bay.
It will also notify you almost immediately if you have a problem. Keep the bait in the traps fresh and if you start to notice pests, pick the ripe fruits promptly.
Choose Early-Ripening Varieties
If you’re growing raspberries, an early-ripening variety may not be available. However, if you’re growing other fruit-bearing plants, like blueberries or strawberries, and are suffering from SWD, consider growing an early-ripening variety.
By choosing a fruit that is ready to go earlier in the season, you’ll reduce your likelihood of SWD becoming a problem simply because they aren’t around yet.
Cover Your Plants
You may be able to prevent the flies from landing by covering your plants with a very fine row cover before the fruit even begins to appear on your plants. Be sure to close it off so that flies cannot get underneath it. This method, however, can sometimes pose problems with air circulation.
If you don’t want to use row covers, you can also just use very fine netting. This will protect SWD from appearing and will also reduce the likelihood of further infestation once an initial sets in. You’ll have to open the netting at each harvest, which can give SWD temporary access to the berries, but this is unlikely.
An added benefit of using row covers or netting is that it will protect the berries from birds and from hail, too, which can be just as destructive as SWD, depending on where you live.
Remember, you don’t have to worry about removing the covers for pollinating because raspberries are self-pollinating.
Refrigerate Your Harvest
If you notice raspberry worms, one of the best ways to halt an infestation is to pick the ripe fruits as soon as you can – and then refrigerate or freeze the harvest. The cold will stop the development of the eggs and freezing can kill them altogether.
Use the Flotation Method
Although most experts agree that eating a few SWD worms won’t hurt you, it can be “icky” to say the least! To figure out whether your fruits are infested, there’s a simple procedure you can follow.
Take about 30 ripe fruits and put them in a gallon bag. Add a cup or two of sugar syrup (½ cup sugar and 1 quart of water) to the bag. Seal it. Mash the berries, then let them settle to the bottom. Any bugs present should float to the top.
This method won’t work with fruits that are already damaged or rotten. Of course, it won’t work for fruit you plan to eat fresh, either! But if you’re worried about a large scale infestation in your harvest, it’s a good way of ruling it out in a small batch before you eat the other ones.
Harvest in Spring Instead of Fall
Fruit flies tend to be more of a problem with Fall crops, particularly beginning in July. If you have an Everbearing variety, you might want to prune them after the Spring harvest so that you don’t get a Fall harvest that would attract the SWD.
There are two organic insecticides which have been found to be helpful in reducing SWD population: Entrust and Pyganic.
Stay away from Spinosad, since it can harm beneficial pollinators despite the fact that it is totally safe for humans and approved for organic use.
If you decide to spray, know that you will probably have to do more than one application and potentially use various insecticides, as insecticide resistance is common. The insecticides, however, target adults before they lay their eggs but they will not control larvae that are already inside the fruit – just something to keep in mind.
As soon as larvae get inside the fruit, your only option is sanitation to prevent SWD from coming out.
Another Type of Raspberry Worm – the Raspberry Beetle
Another type of raspberry worm to be aware of is the larvae of the raspberry beetle. These pests grow to about ⅕ of an inch in length and are quite easy to differentiate from SWD because, of course, they are beetles instead of flies.
These pests have red-brown bodies with fine hairs, feeding predominantly on the leaves of raspberry canes instead of the berries. They tend to mate near the flowers of the plant and leave their eggs behind there.
One of the easiest ways to determine if your pest problem is due to the raspberry beetle or the spotted wing drosophila is to look at the timing and extent of the damage. If damage appears in the spring, from mid-April to early May, chances are that it’s raspberry beetles causing you problems. If damages arise later in the summer, it’s probably SWD.
Fortunately, the damage from the beatles itself usually isn’t anything to worry about – although you will want to keep an eye out for their worms. The worms bury into fruit caps, causing them to die and shrivel up. These pests can also overwinter in the soil and come back the following year.
Fortunately, the steps to get rid of this kind of raspberry worm is more or less the same as the ones you would follow to get rid of SWD. Good preventative measures like pruning, disposing of infected plant parts, and using row covers (and diatomaceous earth!) can keep these pests at bay.
There is one additional method of control that you have in your arsenal when it comes to dealing with raspberry beetles as opposed to SWD. You can handpick them. While this is not usually possible with SWD, you can kill raspberry beetle worms by dropping the beetles (and of course their worms) into buckets of soapy water.
Be Patient – But Be Aggressive
I can’t tell you how frustrating it is to pick quarts and quarts of gorgeous red berries just to open them up and find worms crawling all over them. I’ve continued soaking them in the salt water solution and rinsing, rinsing, rinsing, until all of the worms are gone- then freezing them. This is just one of those mind over matter deals. I’ve resolved that if I end up eating a couple of worms, as long as I didn’t see them first, I’m good with that. Next year, I hope to be ahead of the game.
What about you, have you had trouble with worms in your berries this year? What are you doing to treat the problem?
updated 08/07/2020 by Rebekah Pierce
A city girl learning to homestead on an acre of land in the country. Wife and homeschooling mother of four. Enjoying life, and everything that has to do with self sufficient living.