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Spatial And Temporal Fate of Granule Carriers and Pesticide Availability In Turfgrass

Timothy J. Gibb, Linda J. Mason and Wayne G. Buhler

Objectives

The objectives of this study were to determine the fate of granule carriers commonly used in the formulation of turfgrass insecticides, and to measure the rate at which insecticides may be released from their granule carriers under field conditions.

Rationale

Residential home owners, recreational turfgrass managers, the golf course industry and sod-farm operators rely almost entirely on pesticides in order to manage their insect, pathogen, and weed pests. A majority of these pesticides are applied in a granular formulation. The widespread use of granular pesticides for the control of turfgrass pests has been suggested to be a serious potential threat to the welfare of non-target organisms, especially birds, that may directly or inadvertently consume granules as a source of grit or food. To measure the availability of granular pesticides to birds, consideration must be given to the factors that affect the exposure and toxicity of granule pesticides to birds that use turfgrass areas as foraging arenas.

How It Was Done

Experiments were conducted using four granule types on two turfgrass species. After application, granules were tracked. Specially dyed granules were used to enhance video and photograhic images that captured movement and fate of granules over time. The effects of irrigation, carrier type and turfgrass substrate were monitored at regular intervals over a two week period. Non-dyed granules, subjected to the same environmental conditions, were collected from turfgrass plots at regular intervals and chemically analyzed to measure the release rate of the insecticide active ingredients from their granule carrier.

Results to Date

Granule movement and persistence is dependent upon all factors studied in this experiment. Over time, granules filter down through the grass blades into the thatch. Mowing practices and turfgrass varieties were shown to affect the distance that the granule moves. The most important factors, however, which affect granule movement, breakdown and the release of the chemical from the carrier are; irrigation and granule type. Biodac carriers breakdown very quickly and thus represent little hazard to birds after 12 hours. In summary, using biodac as a carrier, together with immediate irrigation and application to taller turfgrasses can greatly curtail or prevent the incidence of bird toxicity from exposure to granular insecticides.

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