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

Abstract

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 (DLI m ) 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 DLI m 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 DLI m were noted during summer compared to fall for all cultivars in the study. The DLI m were generally higher for bermudagrass than zoysiagrass cultivars. 'Tifway' required the highest DLI m (ranging from 23.5 to 27.2 mol m −2 d −1 ) of the bermudagrasses. 'TifGrand', 'Celebration', and 'Latitude 36' showed comparable DLI m during summer and fall. Fewer consistent differences were detected between zoysiagrasses, with 'Zorro' and 'Zeon' showing the lowest summer DLI m (18.1 and 19.1 mol m −2 d −1 , respectively) and 'Geo' showing the lowest fall DLI m (11.7 mol m −2 d −1 ). Trinexapac-ethyl reduced DLI m only in Zorro, 'Palisades', and 'JaMur' zoysiagrass, but had no effect on bermudagrass DLI m . The DLI m 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, seasonalbased, warm-season turfgrass cultivar selection for shaded environments.

Minimal light requirements and performance under reduced photosynthetic photon flux of GA2ox‐transformed and conventional Kentucky bluegrass

“…In heavy (70% and 90%) shade, TQ generally declined from July to October for both cultivars, likely due to the increasing duration of exposure to low‐light conditions. In general, more favorable turf performance has been reported for short‐term compared to long‐term (or permanent) shade conditions (Bunnell et al., 2005; Chen et al., 2021; Chhetri et al., 2019; Zhang et al., 2017). Although shading lasted 4 months per year in this study, PV performed well in both 70% and 90% shade levels in this study, whereas CONV KBG TQ ranged from 4.0 to 6.6 under 90% shade, PV maintained quality of 6.0–7.9 under these shade levels.…”

“…In addition, previous research has shown application of trinexapac‐ethyl (a GA inhibitor) resulted in increased leaf chlorophyll contents of NuStar KBG (Ervin & Koski, 2001). While GA2ox transformation effects on shade tolerance of turfgrasses have been limited to a single creeping bentgrass study (Studzinska et al., 2012), trinexapac‐ethyl application has shown significant improvement in shade tolerance of both cool‐season and warm‐season turfgrasses (Chen et al., 2021; Qian et al., 1998; Steinke & Stier, 2003a, 2003b; Stier & Rogers, 2001).…”

“…However, the observed PV DLI m is within range of that reported for more shade‐tolerant species including Zoysia spp. (Chen et al., 2021) and turf‐type tall fescue (Meeks et al., 2015), both of which were also conducted using neutral density shade treatments. The CONV KBG DLI m in this study showed light requirements comparable to those previously reported for less shade‐tolerant turf species including bermudagrass and creeping bentgrass (Chen et al., 2021; Russell et al., 2019; Zhang et al., 2017).…”

“…Although a non‐transformed control was not included in the study, the results suggest that the overexpression of the GA2ox gene may contribute to improved turfgrass performance under shaded conditions. It is also important to note that while similar experimental approaches (use of neutral density shade treatments) have been taken to estimate cultivar DLI m in recent years (Chen et al., 2021; Russell et al., 2019), direct application of these findings to vegetative shade environments may be challenging due to lack of light quality alteration in these studies. Given the absence of previously published KBG DLI m data, this is also one of the first field studies to evaluate minimal light requirements of CONV KBG cultivars.…”

“…(Chen et al, 2021) and turf-type tall fescue (Meeks et al, 2015), both of which were also conducted using neutral density shade treatments. The CONV KBG DLI m in this study showed light requirements comparable to those previously reported for less shade-tolerant turf species including bermudagrass and creeping bentgrass (Chen et al, 2021;Russell et al, 2019;Zhang et al, 2017). Previously published DLI m data for KBG cultivars are limited, however, Meeks et al (2015) reported a DLI m of 24.1 mol m −2 day −1 for Kenblue KBG based on a short-term Texas greenhouse shade study.…”