Daily light integral requirements for bermudagrass and zoysiagrass cultivars: Effects of season and trinexapac‐ethyl

Shade is a major problem facing turf managers worldwide. Availability of low‐cost devices and methods for quantifying daily light integral (DLI) offer the turf manager the ability to more precisely determine DLI levels in shade, yet minimal DLI requirements for acceptable turf quality (DLIₘ) for many commonly used warm‐season turf cultivars grown under longer‐term chronic shade stress have not been extensively tested. The objectives of this 2‐yr field shade study were to (a) determine effects of growth regulator trinexapac‐ethyl (TE) and season (summer or fall) on DLIₘ of nine commercially available bermudagrass (Cynodon spp.) and zoysiagrass (Zoysia spp.) cultivars; (b) determine effects of shade level and TE on summer percent green cover and root growth; and (c) determine effects of shade treatments on soil temperatures across the growing season. Significantly higher DLIₘ were noted during summer compared to fall for all cultivars in the study. The DLIₘ were generally higher for bermudagrass than zoysiagrass cultivars. ‘Tifway’ required the highest DLIₘ (ranging from 23.5 to 27.2 mol m⁻² d⁻¹) of the bermudagrasses. ‘TifGrand’, ‘Celebration’, and ‘Latitude 36’ showed comparable DLIₘ during summer and fall. Fewer consistent differences were detected between zoysiagrasses, with ‘Zorro’ and ‘Zeon’ showing the lowest summer DLIₘ (18.1 and 19.1 mol m⁻² d⁻¹, respectively) and ‘Geo’ showing the lowest fall DLIₘ (11.7 mol m⁻² d⁻¹). Trinexapac‐ethyl reduced DLIₘ only in Zorro, ‘Palisades’, and ‘JaMur’ zoysiagrass, but had no effect on bermudagrass DLIₘ. The DLIₘ for a number of cultivars were higher than those previously reported in the literature, which may be attributed to lower mowing heights and/or use of permanent shade structures that were not removed for the duration of the 27‐mo study. The findings should benefit turf managers by guiding data‐driven, seasonal‐based, warm‐season turfgrass cultivar selection for shaded environments.