Uptake and persistence of imidacloprid in grapevines treated by chemigation

The uptake and persistence of a systemic formulation (240 g l−1 SC) of imidacloprid was studied in grapevines treated by chemigation, with the objective of defining suitable application rates for control of the glassy-winged sharpshooter Homalodisca coagulata Say. The sharpshooter is an important vector of Pierce's Disease in southern California, and insecticide treatments are necessary for effective management of insect populations and disease transmission. Uptake of imidacloprid was most rapid at the highest rates of application (281 and 562 g ha−1), reaching target threshold levels within the xylem fluid of 10 μg l−1 within 2 days in younger vines (4 years old). At 141 g ha−1, however, uptake was slow and threshold levels were not achieved in every vine. In older vines (20 years old), 6–8 days elapsed before threshold levels were detected in vines treated with 281 and 562 g ha−1. Despite the initial delay in uptake, once the target threshold was reached, it was maintained throughout the season. It is clear from available information on the population dynamics of the glassy-winged sharpshooter, particularly relating to its seasonal movement from citrus orchards to neighboring vineyards, that appropriate timing of insecticide treatments can play a crucial role in the management of this pest.