Evaluating deterrent effects on pollinator contact exposure to fluorescent powder in white clover ( <i>Trifolium repens</i> )-infested turfgrass

Abstract Pollinators are susceptible to insecticide residues when foraging on weedy flowers in turfgrass systems. Deterrent practices may mitigate this risk by reducing pollinator visits; however, their effectiveness in limiting contact exposure of pollinators has not been thoroughly evaluated. Two trials were conducted using a randomized complete block design with three temporal blocks to assess the effectiveness of deterrent practices in preventing contact exposure of actively trapped honey bees ( Apis mellifera ) and passively trapped insects to fluorescent powder–treated white clover ( Trifolium repens L.) inflorescences in turfgrass. Deterrent treatments included mowing the same morning before fluorescent powder application; spraying with a premix of 2,4-D, MCPP, and dicamba 2 d before powder treatment; or no deterrent before powder application. Fluorescent powder was extracted from 1,440 honey bee specimens collected by active trapping at 4 and 28 h after treatment. Mowing and synthetic auxin herbicide pretreatment reduced the number of fluorescent powder–exposed honey bees by at least 75% and 93%, respectively. Among exposed honey bees, mowing and herbicide treatments reduced powder concentration by at least 75% and 90%, respectively. Honey bee visitation was positively correlated with T. repens inflorescence density, explaining 81% of visitation variability. Mowing transiently decreased T. repens floral density by 85%, but recovered by 7 d, while herbicides resulted in complete loss of floral resources by 7 d. Blue vane traps captured 1,117 bees from 23 species, of which greater than 96% were native, while yellow sticky cards collected 384 insects from the Lepidoptera, Diptera, and Coleoptera orders. Despite differences in honey bee exposure, deterrent treatments did not affect the exposure of passively trapped pollinators to fluorescent powder, likely due to strong visual attraction of traps. Results suggest that mowing and synthetic auxin herbicides effectively deter honey bees from T. repens inflorescences, reducing their exposure risk.