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Published online by Cambridge University Press: 03 September 2025
Ultraviolet (UV) floral reflectance plays a crucial role in pollinator attraction and foraging behavior. Turf protection products could alter the UV reflectance of weedy flowers and potentially deter pollinators from visiting treated flowers. This study evaluated the effects of optical brightener, pigmented fungicide, commercially available sunscreen, and turf colorant on the reflectance of three different UV-floral classes of weeds and subsequent pollinator visitation. Reflectance of petal apices in the ranges of UV-A, UV-B, and UV-C, as well as digitally assessed UV-reflecting area, was reduced 47 to 66% by optical brightener at 3% w/v and equivalent to sunscreen for all species having UV-reflecting petals with bullseye patterns, including dandelion (Taraxacum officinale G. H. Weber ex Wiggers) and bulbous buttercup (Ranunculus bulbosus L.) or with contrasting reproductive parts, foxglove beardtongue (Penstemon digitalis Nutt. ex Sims). These UV reflectance reductions were greater than those of pigmented fungicide or turf colorants (≤38%) but less than that of sunscreen applied via atomizer (≥73%). Pollinator visitation to flowers having UV-reflecting petals with bullseye patterns was 61% correlated to radiometric UV reflectance at one d post-treatment. Thus, impacts on UV reflectance are a powerful foraging cue, but other factors such as flower color, nectar rewards, and scent may also contribute. Pollinators visited bullseye-pattern flowers 40, 34, and 10% as often as nontreated flowers 1 d after optical brightener, sunscreen, and atomized sunscreen treatments, respectively, with foraging typically reduced up to 2 d post-treatment. Only slight changes were noted in post-treatment pollinator foraging on the UV-absorbing inflorescences of white clover (Trifolium repens L.). Despite transient impacts to floral reflectance and pollinator foraging visits, treatments did not affect floral density or quality, preserving long-term pollinator food resources. Our findings suggest that multiple bioactive residues could be employed in turfgrass management practices to potentially safeguard pollinators from harmful products.