I've been getting a number of calls lately concerning spotted wing drosophila in caneberries and strawberries, especially from growers on the smaller scale – in most cases organic operations.
Let's do a brief review what the best way to manage this will be:
One should take a two pronged approach. First the use of Entrust (spinosad) as a spray is recommended, while at the same time, to the extent possible, one should be removing the cull fruit (rots and over-ripes) from the field and burying them or throwing them away. For strawberry growers running the tractor over the culls in the furrow can be useful - not so much because it crushes the larvae, but because the flattened fruit dries out quickly and loses its property as a suitable food source. The spray is reducing the number of adults, while at the same time all routes of maturation are no longer available to the fly. Harvested fruit is removed and sold, and cull fruit is removed or destroyed, so there is no way for the larvae to complete their life cycle and turn into more flies.
That said, two years of research tells us to recognize that removal of cull fruit alone will not be enough to bring the population down to acceptable levels. There will always be the one fruit that is missed but yet contains the propagation potential in it to re-infest your field. That is why the best route for you is to spray along with practicing good sanitation.
Final word would be to take note of what is around your field. Are there any patches of uncontrolled spotted wing drosophila next door or wild blackberries? Both of these areas are serving as hosts and it will benefit you to get some control there also.
There is a pesticide mentioned in this article for control of spotted wing drosophila on the small scale. As always, before using such a pesticide, refer to the product label for directions on use.
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