Fruit Crop Protection From SWD

By Scout Nelson

Spotted wing drosophila (SWD) is an invasive fruit fly that has become a major problem for fruit crops in the Upper Midwest. It mainly affects raspberries, blackberries, blueberries, table grapes, and honeyberries. This pest is difficult to control because of its unique biological features.

Unlike many fruit flies, SWD females have a saw-like ovipositor that allows them to lay eggs in unripe fruits. The larvae grow inside the fruit, making it unfit for consumption. After development, larvae may either pupate inside the fruit or drop to the ground. SWD populations grow quickly as their life cycle is short and depends on temperature, allowing several generations in one season.

The pest thrives in humid and shaded environments. Research shows that wooded areas with wild berries can host early SWD populations before they spread to crop fields. Monitoring is essential to detect early infestations. Growers use traps with either commercial lures or homemade mixtures. Homemade traps can be prepared using a plastic cup filled with yeast, sugar, water, and a few drops of dish soap. These traps attract flies, but they are mainly useful for monitoring, not full control.

Fruits should also be checked regularly for larvae. Methods like the salt test help in detecting infestations by separating larvae from mashed fruit samples. This helps in timely decision-making for pest control.

Effective management combines different strategies. Frequent harvesting and removal of damaged fruits help reduce pest spread. Quick cooling of harvested fruits slows larval growth. Proper pruning improves airflow and sunlight, making conditions less favorable for SWD. Managing irrigation leaks also reduces humidity levels.

Growers are advised to follow pesticide guidelines carefully and rotate products based on FRAC numbers to avoid resistance. Detailed management practices and updates are available at the UMN's FruitEdge SWD biology and management webpage and Midwest Fruit Pest Management Guide.

A webinar on recent research and innovative control methods can be viewed here. These resources provide valuable guidance for managing this pest effectively and protecting fruit crops.

Photo Credit: pexels-aiselin82