John Wiley & Sons, Ltd.

Mowing mitigates bioactivity of neonicotinoid insecticides in nectar of flowering lawn weeds and turfgrass guttation

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Systemic neonicotinoid insecticides are used to control of turfgrass insect pests. We tested their transference into nectar of flowering lawn weeds or grass guttation droplets which, if high enough, could be hazardous to bees or other insects that feed on such exudates. We applied imidacloprid or clothianidin to turf with white clover, followed by irrigation, and used LC‐MS/ MS to analyze residues in clover blooms that were directly sprayed during application or that formed after the first mowing. Imidacloprid residues in guttation fluid from field‐grown creeping bentgrass were assessed similarly. We used Orius insidiosus, a small anthrocorid bug that is sensitive to dietary neonicotinoids, as a bioindicator of the exudates' toxicity. Nectar from directly sprayed clover blooms contained 5493–6588 ng/g imidacloprid or 2882–2992 ng/g clothianidin and was acutely toxic to Orius. Residues were 99.4–99.8% lower in nectar of blooms formed after mowing, and non‐toxic to Orius. Imidacloprid residues in turfgrass guttation averaged 88 ng/g at 1 wk after treatment, causing some intoxication of Orius, but declined to 23 ng/g within 3 wk. Systemic transference of neonicotinoids into white clover nectar and creeping bentgrass guttation appears relatively low and transitory. Hazard to non‐target insects via nectar of flowering weeds in treated lawns can be mitigated by adhering to label precautions and mowing to remove blooms if they are inadvertently sprayed. Environ Toxicol Chem © 2014 SETAC

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