Spotted wing drosophila (SWD) is now the number one insect pest of berry crops in Wisconsin, most other states, as well as many parts of the world. Management practices are pretty labor intensive and costly and tend not to provide adequate control. Many growers rely primarily on insecticides to manage this pest.

In organic production, an emphasis should be placed on monitoring, sanitation, regular picking, exclusion netting, strategic selection of cultivars, and finally chemical controls.

Monitoring, using homemade or commercial trap and baits, should be implemented to monitor for first occurrence and to help determine the efficacy of, and when to reapply, management practices. For more information on this refer to the SWD website.

We discussed several of these topics in previous articles. Sanitation was discussed along with the importance of timing in harvest schedule in a previous article. The main points there are: to harvest every 1-2 days for optimal yield and minimal SWD infestation, and to bag culled fruit for 32 hrs to kill 99% of the larvae, regardless of the color of the plastic used to bag the fruit.

A physical barrier such as exclusion netting can prevent flies from reaching the fruit. A mesh size of less than 1mm can provide 100% protection against SWD when applied adequately. More detail on exclusion netting can be found here. We also discussed how certain varieties may avoid SWD infestation by ripening earlier than the peak of SWD populations. Earlier fruiting cultivars of raspberry and blueberry have showed overall lower levels of infestations and some may completely avoid infestation if harvest occurs before July. More can be found on this topic here.

When it comes to chemical control in organic production, there are few NOP-approved insecticides available that provide some control of SWD. These include Entrust (spinosad), Grandevo (Chromobacterium subtsugae) and Pyganic (Pyrethrins). Entrust is the most effective OMRI-approved insecticide and must be rotated with another insecticide, such as Grandevo or Pyganic, after two applications of Entrust, to achieve some resistance management. There are several restrictions on the use of Entrust that vary per crop, so please check the label carefully and follow the instructions.

Insecticide application intervals should be short, every 4-5 days and spray coverage and timing is critical to achieve optimal control. Applications should be done early morning in the bottom part of the crop or late afternoon throughout the crop, to target prime activity time and location of the flies, and avoid pollinator activity during the day.

Finally, picked berries should be cooled to 35°F as soon as possible to stop further development of the immature SWD inside the fruit. We recommend to cool fruit for three days to increase mortality of larvae present inside the fruit. If you sell fruit directly to consumers, advise them to keep fruit in the refrigerator. Freezing fruit will kill all stages of SWD. All these management practices are compatible and should also be considered in conventional production to optimize management of SWD.

Other resources include: A recent webinar on organic management of spotted wing drosophila is available at this link from eOrganic. This webinar discusses the latest research on organically approved management strategies for SWD. And more information on organic management can be found in this article from Michigan State University.

This article was posted in Insects and tagged SWD.