Guest post by Jeanie Schwenk.
Elderberries, SWD, and How to Prevent Without Pesticide Use.
Spotted Wing Drosophila [ SWD ], is a fruit fly that destroys soft skinned fruits by laying their eggs in the ripening fruit using their serrated ovipositor. The larvae mature in the fruit, ruining the fruit which becomes mushy and gives off the unmistakable smell of rotting fermented fruit. SWD have a short reproduction cycle so depending on the climate, they can produce between 4 and 10 generations in a season.
SWD can destroy an entire crop so controlling them is essential. The options for controlling are:
1) trap for them checking your traps weekly to know when SWD are present.
2) harvest thoroughly, remove all fruit from the ground and from the plant and dispose of by burning, freezing, or burying 2 feet deep.
3) Use pesticide (pyrethroids, spinosyns, and organophosphates) every 7-10 days during ripening to control the reproduction rate if you find evidence of SWD. These flies can complete their lifecycle in 21 to 25 days and can live for up to 66 days so once they are present, they are virtually impossible to eradicate even with pesticide use. Because SWD can produce so many generations per season, they may develop resistance to chemicals so it is recommended to alternate the type of pesticide (alternate methods of action).
SWD information links: OSU (Oregon), WSU (Washington), MSU (Michgan), MU (Missouri)
Trapping is considered insufficient for controlling, but there has been a report from Japan that intensive trapping (60 – 100 traps per acre) decreased the SWD numbers. Although traps need to be checked and the bait needs to be replenished weekly, this may become a part of the solution.
In 2013, as we were checking our elderberries (four varieties) to see if we could start harvesting, we discovered we had SWD. The week prior, we had not. SWD took our entire 2013 crop. There’s a place about 10 miles away where we knew of some wild ones, but they were also infested. We were extremely disappointment as our family uses homemade elderberry tincture liberally especially during flu season.
How to Protect Your Elderberries.
After researching SWD, the accepted control options, and the reasons behind each option, we weren’t left with anything we found acceptable. Trapping to determine if we had them, easy. Harvest thoroughly and destroy any leftovers or damaged crop, easy. Pesticide use is where they lost us. Although pesticides may be the only option for large farmers from a cost perspective, we’re small so I decided to run an experiment of “bagging” even with the literature out there stating that it’s not an option due to the size of the fly.
There weren’t any pre-made bags on the market with the holes per inch needed to prevent the SWD from getting in AND also keep the ovipositor from obtaining access through the bag. The hole size needed to prevent them from accessing the fruit must be less than 0.98 mm. Since we’d lost all of our 2013 crop, we figured we didn’t have anything to lose except our time, energy, and little money. Because we wanted to determine in one season what would work and what wouldn’t, I designed and sewed four types of bags in a variety of materials, using a variety of sizes, various edgings, stitch types and lengths. We know the size of the fly, and we know the size of the ovipositor, so it made sense that if we had the right type of materials, we could prevent them from accessing the ripening fruit.
Bagging Experimentation and Results.
Before the fruit ripened, we bagged (and bagged and bagged) the elderberry clusters. Some were starting to change color while others were completely green. Each type of bag worked at preventing SWD. We did leave some clusters uncovered so we could determine conclusively that we had SWD again in 2014. We did have them, but only in the unbagged clusters.
The one down side was that the third year canes had the largest clusters, but were also the most brittle wood so we lost some canes as the bags with the edging did add weight (especially when wet and it rains a lot here in Oregon). The canes that held the bags without edging had no issues. The edging turned out to not be necessary to keep the SWD away from the ripening fruit. Next year, we will only use the bags without edging to protect our elderberries. I made different sizes (small, medium, and large) but the ease and speed of applying the larger bags to the fruit won out against using the material as conservatively as possible. The bags with a more tailored approach (in the shape of a cluster) were far too difficult to apply and took more time to cut out and sew together, so after all our false starts, applying the bags, and harvesting, our final product is made from the darker mesh and has no edging. The white mesh is military grade at 1800 holes/inch. It is much more difficult to sew, it is harder to see through to the fruit, and it also retains more water putting stress on the canes.
We will be taking the bag approach even though it is time intensive for a short period of time in the early summer because we can rest with the assurance that we’ll have an SWD-free harvest and the berries will be pesticide free.
The bags are re-usable; I should get a minimum of 3-5 years use out of them. I washed, checked for holes and will be using them again in 2015. We are considering selling these bags if there is enough interest, however, due to the cost of the materials, this may not be a cost-effective solution. It is the only solution for us as we don’t want to use any pesticide, even the organic ones. There are bags out there but the holes/inch ratio is not small enough to keep out SWD. If you already use a pesticide or insecticide, what does it cost per acre in pesticide and labor to keep the pests away? If you are interested in bags for your elderberries, please email me at email@example.com and give us your input.