Biological Control of Spotted Wing Drosophila (SWD) on berries and fruits

The good news that I want to share with all interested soft fruit and berry growers is that there is an effective biological SWD predator that is environmentally safe, commercially available and highly effective at interrupting the reproductive cycle of SWD at a cost of less than $100 per treated acre.

Raspberries are critical to the SWD garden population explosion, serving as a magnet crop for SWD egg-laying during the early to mid season. And the fragility of raspberries during the 2-3 week SWD development cycle means that most SWD larval and pupa development will occur in the soil of the growing beds, rather than on the off-the-ground fruit.

Field Report:

I am reporting on my experience with an effective biological control method for SWD – tested in a 6-year field trial with my home garden raspberries in western NC.  My first awareness of SWD on-site was in 2015 and by 2016 my ripe raspberries (and other fruits) were heavily laden with SWD larvae. But after two annual Sf nematode drench applications to all raspberry beds in 2016 and 2017, my berries have been largely free of SWD larvae (based on examination of berries collected for home use) from 2018 through the 2022 crop season – without the recommended additional predator applications. And this success continued through all my berry collections of 2023.

I realize that this successful field experience may be considered as anecdotal, so I am encouraging other growers and IPM scientists to examine this proposed “treatment” for SWD to see if my observations can be replicated elsewhere. Certainly, having access to a commercially available and biologically effective SWD predator would be beneficial to organic fruit growers, both home and commercial.

On the IPM management side, I hypothesized that nematode predator effectiveness would be high for raspberries, and other fruits that could not support the full reproductive cycle of SWD off-the-ground. And nematode research in the laboratory shows that each parasitized SWD larva will produce thousands of new Sf predators in the soil.  So for the first two years after Sf applications, instead of the conventional strategy of removing and disposing of any SWD-infested raspberries, I returned them to the soil of the growing beds to fuel nematode population growth.

On the speculative IPM side, my experience suggests that Sf in raspberry beds could contribute to an intergenerational “attract-and-kill” program for SWD – by attracting reproducing SWD adults to the ripe berries and disrupting the ensuing SWD reproductive cycle in-the-ground. And perhaps the resulting population reduction in SWD might benefit other fruits as well? (I am seeing no SWD larvae in blueberries and figs in the garden area that were heavily SWD infested in 2016, but not directly treated with Sf.)

Reported by Patrick Horan, Sapphire NC