Identifying Spotted Wing Drosophila (SWD) in Your Fields

Spotted Wing Drosophila (SWD) is a significant pest that poses a threat to small fruit crops in the Pacific Northwest. SWD infests ripe and overripe fruit by laying eggs beneath the fruit surface. The subsequent development of larvae leads to unmarketable fruit. Through extensive research, we have gained valuable insights into SWD behavior and risk factors, enabling us to devise effective management strategies to mitigate economic losses.

Throughout the growing season, SWD populations increase, leading to heightened field pressure. Early-season crops experience minimal risk, whereas late-season crops are at a considerably greater risk. SWD populations can vary significantly based on geographic location and surrounding habitats, with numerous ‘risk factors’ related to cultural practices and landscape attributes critically influencing individual field pressures.

Optimal conditions for SWD typically occur within a temperature range of 64 to 82 degrees Fahrenheit, during which active breeding is most prevalent. Conversely, extreme temperatures and dry, windy conditions with high UV exposure can drastically reduce their populations/pressure. SWD migrates from bordering habitats into field edges. While they may lay eggs in the field where there is an abundance of breeding hosts, open environments are not ideal for their populations, which predominantly thrive in densely vegetated areas.

Monitoring is crucial, as it can detect low populations before they reach economic or market detectable levels. There are various effective field management tools available for controlling both the adult and larval stages of SWD.

• Types of crops (e.g., blueberries, caneberries, strawberries): Blueberries, with their harder skins and exposure to weather, are generally less susceptible than softer-skinned caneberries.
• Cultivar seasonality: SWD populations typically build throughout the season, meaning early-harvest cultivars encounter lower field pressure compared to those harvested later in the season.
• Cultivar growth habit: Dense canopies with closely packed and shaded fruit are more susceptible to SWD.
• High crop diversity and density in small blocks may raise risk, as SWD can migrate between closely planted crops as fruit ripens.