Turfgrass As a Possible Route for Pollinator Exposure to Lawn-Applied Imidacloprid.

There are numerous recognized routes for pollinator exposure to insecticides, not least of which includes treatments to flowering plants within home lawns and gardens. However, beneficial insect exposure to insecticides via guttation, the exudation of xylem-transported sap, is a more recently identified route of exposure in corn and wheat. Little is known of its role in other grass species, including those most common in southern turfgrass landscapes. Imidacloprid is a common home and commercial neonicotinoid insecticide used for the control of turfgrass insect pests that can possibly be translocated into guttation fluid, potentially harming non-target insects.

An experiment was conducted to investigate the fate of soil applied imidacloprid within ‘Tifway’ hybrid bermudagrass (Cynodon dactylon × C. transvaalensis) and ‘Palmetto’ St. Augstinegrass (Stenotaphrum secundatum) to explore whether levels of imidacloprid translocated to guttation fluid exceeds levels that are reportedly toxic to foraging pollinators. A greenhouse experiment was conducted as a completely randomized design, with six treated and six non-treated experimental units of both turf species.  Turfgrass was sub-irrigated with 1 L of either water or a dilute imidacloprid solution (0.59 mg imidacloprid / L) within 1.3 m² plastic flats, which is representative of a standard home-lawn application rate. Guttation fluid was collected 48 hours after treatment. Imidacloprid concentration was determined via mass spectrometry. Means are presented ± a 95% confidence interval (CI).

Guttation collected 48 hours after treatment from bermudagrass and St. Augustinegrass contained 15.8 (± 0.7) and 13.7 (± 8.8) ppb imidacloprid, respectively, which is substantially less than concentrations reported to be lethal to the European honeybee and the insidious flower bug (LC₅₀ 1760 and 5493 ppb, respectively).  However, measured concentrations are similar to those associated with sub-lethal effects in honey-bees (10 ppb). Future research will evaluate imidacloprid concentrations of more commonly practiced foliar applications.