Spotted wing drosophila (SWD) control in strawberries and raspberries: a grower's advice

(adapted from a presentation to the Ontario Berry Growers Association Annual Meeting February 2013)

Spotted wing drosophila (SWD) is a pest that will become more problematic as the summer season progresses. I like to compare them to mosquitoes, there are always a few in May and June, with increasing populations as conditions become more favorable. In 2012, the early spring brought earlier identifications in traps and crops. Later starts will result in later pressure points. In 2012, above average temperatures delayed and prohibited egg laying. SWD isn't active when temperatures exceed 30-32 °C. As we become more familiar with its habits, we will modify our harvest schedule and crop protection applications.

Consequently, most of the June strawberry harvest shouldn't be affected. However, berries that aren't harvested on a timely basis, especially in mid to late season, will be a source of habitat for populations to increase. Evidence suggests that strawberry skins tend to be tougher and more difficult for the female to penetrate and lay her eggs. One of our most successful strategies to combat SWD hinges on frequent and timely harvest. As soon as a field has finished being harvested, I would recommend beginning the renovation process. As everbearing strawberries begin to be harvested the year of planting, SWD pressure will be moderate to high. A weekly application of crop protectants and harvesting 2-3 times per week is recommended.

Raspberries will only have low pressure at the very beginning of harvest, most early varieties won't be affected much until the last few harvests. Evidence suggests that the softer skin allows female SWD to lay her eggs as fruit turns white to pink. Harvest schedules need to be maintained at every other day intervals. Night time temperatures will determine if pick intervals are increased or decreased. In our fruiting fields, we clean harvest all fields including pick your own before crop protectant applications. When SWD pressure is high and trap counts start doubling, we begin to remove all cull fruit from the field. Similar to strawberry renovation, summer raspberry canes should be removed as soon as harvest is complete. At this time we also removed small primocanes on the edges of the rows that were producing berries. Our strategy allowed us to apply insecticides that had longer preharvest intervals for resistance management. Our goal was to have 1-2 weeks off between summer and fall harvest and apply 1-2 longer lasting insecticides to get SWD populations back in check.

SWD control strategies that are common to both strawberries and raspberries :

  • Maintain weekly crop protectant applications.
  • Maintain frequent harvest schedules.
  • Don't allow over ripe fruit to stay on the vine. Even picking it and leaving in the wheel marks will reduce egg development. Leaving berries under the plant canopy will allow more egg development. The sun will cook a lot of eggs in exposed fruit.
  • Deliver harvested fruit to the cold storage hourly, maintaining temperatures as close to 0°C as possible through the entire cold chain.

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