Drip and Overhead Sprinkler Irrigation in Blueberry as Cultural Control for Drosophila suzukii (Diptera: Drosophilidae) in Northwestern United States

Overhead sprinkler compared to drip irrigation in cropping systems can result in increased relative humidity (RH) and decreased temperature within the plant canopy. Such conditions may also result in a more favorable microclimate for pests. Drosophila suzukii Matsumura is an invasive agricultural pest of berries in America and Europe. Drosophila suzukii is susceptible to high temperatures and low RH, thus its survival may be affected by different irrigation methods. We tested how drip and overhead sprinkler irrigation in blueberries influenced temperature and RH. Furthermore, we determined how these environmental factors affected adult emergence rates from larvae within fruit or pupae outside of fruit. RH was higher in overhead sprinkler compared to drip irrigation treatments, but there was no difference in temperatures. Although there were no differences in fly emergence from larvae between irrigation treatments, more flies emerged from pupae in overhead sprinkler compared to drip irrigation treatments. This is likely because larvae developing inside fruit are protected from desiccation, while pupae were exposed to lower RH. Regardless of irrigation method, temperatures remained above 30°C for longer periods and RH was lower above as opposed to below the mulch. Fewer D. suzukii larvae and pupae consequently survived above the mulch than below the mulch. When assessing natural infestation, we found similar numbers of D. suzukii flies emerging from blueberries collected on drip and sprinkler rows. Irrigation management can be coupled with other cultural control methods that ensure that pupae remain exposed on low RH surfaces, where they are more likely to succumb to desiccation.