Thought people might like this.
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That is very good news; talk of these SWD parasitics has been going on for at least ten years.
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Hopefully, the winds will pick some of them and blow them towards the east coast. More likely some will stow away on a fruit truck though for faster dispersal.
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Biocontrol of SWD
I am a bit late to this discussion, but SWD don’t “go away” with standard cultural practices! So some may be interested in a biological control organism that can effectively control SWD via the reproductive cycle, using a commercially available predator and strictly organic methods.
My recommendation is based on my own 6 year “field trial”. I applied this soil-based predator (Steinernema feltiae) to my western NC raspberry beds in 2016 and for the last six years I have seen no SWD larvae on the fruit!
The predator works by attacking and parasitizing the SWD larvae and pupae developing in the ground. So it works best with soft fruits. And predator survival will require a growing bed that is chemical-free with no pesticides or residues (or other chemical toxins).
This beneficial nematode is easily applied by soil drench to the growing beds. And it can be used to treat a growing area of up to an acre for less than $100. (Sf is available from several beneficial insect sources, such as Arbico).
This control of SWD has brought joy back to my life as an organic berry grower/consumer! I hope that others will find it useful.
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For those that are into predators like me…
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Interesting anecdote by pmhncSWD above, but
^ needs frequent applications
and from
“while Steinernema feltiae and Heterorhabditis bacteriophora are not effective in controlling the target dipteran.”
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Thank you for the notes on the SWD biocontrol issue. I agree that any issue as important as this warrants careful, critical attention to scientific research issues and sources as well as conclusions.
While a 6-year real field experience “anecdote” may be difficult to interpret, the same can be said for laboratory research reports which are highly structured, but detached from real world issues and situations.
For example, the primary conclusion of the GFG blueberry article cited above was that S feltiae was very effective in SWD control in both lab and field trial:.
“Quintanilla’s team has tested two entomopathogenic nematodes, both commonly available as biocontrol spray products. One, Steinernema feltiae, was very effective in trials, while the other, Heterorhabditis bacteriophora , was less effective. S. feltiae caused a significant reduction in SWD adult emergence in both lab and field trials”.
However, the second cited article reached a contrary conclusion about S feltiae effectiveness, go figure! …
On the “frequent predator applications” issue, my field intervention involved S feltiae applications in late June of 2016 & 2017, when SWD larvae were present. No larvae were observed in subsequent years 2018- 2023). So no additional predator applications were needed. SWD is under control.
More generally, beneficial nematodes’ capacity for exponential population growth in the presence of an ample food supply is well-established: “Once inside the infected insect, nematodes develop rapidly, in five or more days, depending on host quality and temperature. Normally, one to two generations occur in a host insect. Thousands of nematodes can be produced following a single infection.”
Source www.extension.colostate.edu/docs/pubs/insect/05573.pdf
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The below shows how to grow these insect eating nematodes on wax moth larva. ( sold as fish bait )
This seams like a good way to check viability of purchased nematodes, and at the same time multiplying their numbers many fold
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All SWD control large-scale experiments to-date have resulted in a % control, and usually not a very high %.
The problem with nematodes for the home gardener is the narrow range of soil moisture and temperature for them to be effective.
Is it possible to examine the soil for live nematodes to see if you are being successful?
Otherwise you just have to wait and see what the pest population becomes, and then it is too late.
Spraying and trapping have more immediate, visible results.
Any abundance of parasitic wasps would be readily visible.
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There is a lot of diversity in proposed SWD control efforts and in the estimated efficacy of those efforts. But most current research efforts involve the adult SWD as the object for control. My proposal for soil-based control using the Steinernema feltiae beneficial nematode focuses on the SWD larvae/pupae as the targets for control, thus cutting off the SWD reproductive cycle. And my field experience with the absence of SWD in raspberry beds for six years after release of these nematodes, suggests (to me) a high level of efficacy in this approach.
Both adult population control and reproductive control strategies for SWD could be pursued simultaneously if desired. It need not be a matter of choosing one over the other (for practical, as opposed to scientific, purposes). The main soil requirement of S. feltiae is for moisture-retaining materials in the top 3-4 inches of soil. But isn’t that what we would want for good raspberry growing conditions, as well? And it appears that last winter’s -3 F low here in the WNC mountains did not kill the existing S.feltiae in my raspberry beds, as my first raspberry harvests in 2023 have been free of SWD larvae. But annual reapplications would not be a severe burden if needed in colder climates.
Steinernema feltiae is a microscopic roundworm, so it is not amenable to hand examination and counting in treated soil. And the smallest available commercial release is ~5 million beneficial organisms which is recommended to treat 1600sf (Arbico Organics). So the first evidence of efficacy could come possibly with a Fall red raspberry crop, or certainly the following Spring/Summer.
Update: I am being blocked from submitting a reply to the LarryGene comment below???
But I would like to agree that the strategy of stopping the SWD reproduction cycle in the soil is more effective than the conventional Attract-and-Kill IPM strategies directed toward SWD adults. And placing or leaving the SWD infested fruits on the ground of the planting beds is the best (and cheapest) way to grow your predator population. (See my CSU note above about each parasitized SWD larva producing thousands of additional nematodes.)
In effect, this biocontrol strategy is an intergenerational Attract-and-Kill for SWD - attracting the adult generation to lay eggs on ripening berries, and then killing the developing SWD larvae/pupae in the ground. Plus this “natural” strategy requires no further effort or intervention on the part of the grower. And after a few cycles, the SWD population should be dramatically reduced.
Of course using this strategy in areas with prior use of insecticides or other chemicals may be problematic, by killing the predators as well as the pests.
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Stopping SWD at the soil line would be ideal. This whole SWD-in-the-soil process must be at a very shallow level and I have wondered if, for the home gardener, torching the soil surface at the first appearance of trapped SWD adults would be effective.
Over the past ten years, I have used vinegar traps, pruning out all interior fruit clusters (leaving sun-exposed exterior clusters), leaving a few “bait” berries on the ground and then blasting those with flying insect spray then placing new bait, and refrigerating fruit to bring larvae to the surface and picking those off before further processing, all as methods of minimizing the larvae in fruit.
I only have a total of 30 row-feet to deal with.
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I agree that the strategy of stopping the SWD reproduction cycle in the soil is more effective than the conventional Attract-and-Kill IPM strategies directed toward SWD adults. And placing or leaving the SWD infested fruits on the ground of the planting beds is a great way to grow your predator population. (See my CSU note above about each parasitized SWD larva producing thousands of additional nematodes.)
In effect, this biocontrol strategy is an cross-generational Attract-and-Kill for SWD - attracting the adult generation to lay eggs on ripening berries, and then killing the developing SWD larvae/pupae in the ground. Plus this “natural” strategy requires no further effort or intervention on the part of the grower. And after a few cycles, the SWD population should be dramatically reduced.
Of course using this strategy in areas with prior use of insecticides or other chemicals may be problematic, by killing the predators as well as the pests.
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To clarify: My “bait” berries are on the ground for no more than 24 hours, then discarded with all adults killed. The reason for putting them on the ground is that is the coolest and dampest location in the berry patch, preferred by the flies. Otherwise I keep all fallen fruit picked up. Easy to do with 30 row-feet, but hard for the gardener with long rows and grassy or weedy growth near the canes.
Do nematodes require clear, manicured soil to thrive or can they be applied into weedy areas?
Then there are the SWD that fly in during the fruiting season from a location outside of the berry patch. These would not be subject to nematode control until the following year.
In many city locations the fly-ns could be numerous considering the high number of untended fruiting plants. A walk down the unpaved alleyways here in SE Portland passes dozens of such trees, brambles, and stray grapevines.
Thanks for the clarification. But with your chemical commitment for SWD control, there is probably no prospect of using ground-based nematodes in your control plans. I don’t know anything about nematodes sensitivity to various insecticides, so I am assuming the worst here.
SWD fly-ins are not a problem for the nematodes, just another food source. When the fly-ins reproduce their developing larvae/pupae are parasitized and this builds the nematode population while reducing the next generation of SWD. After multiple 2-3 week cycles of this reproductive process you will have a much increased nematode load and a much reduced SWD population.
One thing that I am assuming is that raspberries represent an “SWD magnet”, and will be visited and favored for reproductive purposes (because of the timing and accessibility of the fruit). And so early in the season, raspberries will attract SWD from other local SWD domains and sources.
And your location in the Pacific Northwest may open another biocontrol option in the form of the predator wasp Ganaspis brasiliensis, which was featured in the lead article for this discussion. And which has apparently naturalized in some locations. See below
At a NWREC Caneberry Field Day, 8 or 10 years ago, one of the presentations featured a small jar with perhaps 100 live predatory wasps for SWD control. I do not remember the species.
Although the wasp size was similar to a small gnat, I thought they would be readily visible in caneberries when they are on patrol, and I have never noticed them at home.
SWD appears here mid- to late-July and peaks in August (Triple Crown season), persists through October.
It appears that this predator wasp (from South Korea) has cleared APHIS restrictions and is approved for general release. I have no information about commercial availability. But I like that it is a SWD-specific predator, not a generalist.
I am attaching a more detailed, but nontechnical account from “just down the road” in Georgia. I was surprised to find that these wasps target the SWD larvae, not the adults. And they have a 1:1 reproduction rate (one dead SWD larva for one new wasp. I wouldn’t think that this would be sufficient to turn back the massive SWD population outbursts that we see in untreated raspberries and other fruits. But we will have to wait for some field reports on this. Certainly the “naturalization” reports from the Pacific Northwest are encouraging!
Meanwhile, S. feltiae is still my SWD biocontrol of choice, because of the 1:1000 reproduction rate and the SWD control effectiveness that I have seen here in the NC mountains. But I appreciate the mobility offered by G. brasiliensis and I would certainly consider it for other locations, if it were available.
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Each wasp probably lays hundreds or thousands of eggs, and they can fly around to target SWD larva, rather than wait for one by at soil level.
I have been dealing with swd for years here in Wv.
My strategy has been to hang 1/2 gal. Milk jugs , with top cut off every 20ft. Or so down the row. I put a pinch of borax in each jug.
When I pick berries or figs , I pick into 2 separate containers,one for good berries, the other for over ripe ( swd infested berries)
When I get to the milk jug I put the infested berries in there.
By the next day most swd are swarming around the milk jug,laying their eggs in there. Which die. And it keeps the adults occupied.
By keeping the rows picked clean frequently , putting all over ripe fruit in the jugs , I have been able to keep damage to a reasonable level .
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I have a garden in an urban situation in southwestern Canada, and we used to have a bad SWD infestation until a couple of years ago. For a couple of large sweet cherry trees, the only option that worked was to cover the trees completely with floating row cover material. Raspberries were the other fruit that attracted lots of SWD, and these were kept reasonably under control by a procedure similar to Hillbillyhort’s. I picked all of the berries that were at least close to ripe, especially any berries on the ground. The decent berries went into one ice cream bucket (4 liter or 1 gallon size), and any showing damage went into another bucket. The bucket with damaged berries was left outside with the lid on and in a sunny location. The combination of heat from the sun and gases produced by fermenting fruit effectively killed any SWD (and Picnic Beetles) by the next day. I kept adding more damaged fruit to the killing bucket until it was pretty full; the more fruit in there, the more noxious gases were produced.
I did this for several years until 2 years ago. The year or two before then, I had noticed a decline in SWD numbers, until 2021, when they had declined enough that I no longer had to watch out for them in the cherry trees or raspberry bushes, except for a short time near the end of the fall rapberry season. It was the same or better last year and so far this year, although I have just started picking ripe rapberries.
Just a couple of days ago, in another thread of this forum, I read about the discovery of G. brasiliensis in British Columbia, Canada, and in Washington. Since I’m located in the region of this discovery, I’m hoping that the decline in SWD numbers is due to the wasp and will be permanent.
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