Cool-Season Water Use With the need to reduce turfgrass water use, the
United States Golf Association (USGA) is partnering with NTEP to evaluate both cool- and warm-season grasses for water efficiency and performance under lower water use. Te USGA has paid to install rain exclusion shelters at ten sites, five in the northern or transition zones (to evaluate cool-season grasses) and five shelters in the southern U.S. to evaluate warm-season grass water use and drought tolerance. Within these shelters, cooperators restrict irrigation for a period of 100 days on cool-season grasses, or 120-150 days for warm-season grasses. Tese ‘drought seasons’ under the shelters are part of Approach 1, which is a measurement of the amount of water needed to maintain a prescribed level of green during that period. Ten trial locations in the drier western U.S. states
(five each for cool-season and warm-season grasses) manage under Approach 2, which utilizes three evapotranspiration replacement rates (ETo
). In Approach 2
locations, researchers replace either 40, 60, or 80 percent of ETo
(as determined by local weather station data) for cool- season grasses, or 30, 45, or 60 percent ETo
for warm-
season grasses. Tis scenario is more typical of irrigation patterns in the western U.S. with 25 inches (635 mm) or less of annual rainfall. Approach 2 data indicates the reduced irrigation level each entry will survive, and at what level each entry will deliver acceptable turfgrass quality. Terefore, the two approaches address the needs
across the U.S., from the humid, eastern U.S. with 30+ inches (762+ mm) of annual rainfall but with occasional prolonged drought periods, to the arid western U.S. where annual summer drought periods are expected. Te warm-season version of this trial was
established at ten locations in the summer of 2018. Te cool-season version of this trial was established in the fall of 2016 or the spring of 2017 at ten total sites, five under rain exclusion shelters in the eastern U.S. (Approach 1) and five in western U.S. field sites (Approach 2). Te cool-season version includes fifteen Kentucky bluegrasses, nineteen tall fescues, and one perennial ryegrass (as a control entry). Te first data from the cool-season trial was
collected in 2017 at six of the ten locations. Four Approach 1 (shelter) locations collected data during a 100-day induced drought period, and in some cases, large differences were noted in the amount of water used by entries, however very small statistical differences were noted among entries. For 2018, we changed the re- watering procedure threshold to 65 percent green cover, as well as expanded our statistical analysis for all sites to include separate Kentucky bluegrass and tall fescue tables. In 2018, all Approach 1 locations noted large differences in the water needed to maintain 65 percent green cover.
Four locations that were unable to collect three
years of data by 2019, concluded their data collection in 2020. Te Fayetteville, AR, site’s (Approach 1) seasonal water needed ranged from 34.0 mm (1.34 in.) to 80.7 mm (3.18 in.) in 2020. No statistical differences were noted among water needed when comparing all Kentucky bluegrass and tall fescue entries. However, there was some statistical significance among tall fescues when compared only to other tall fescue entries. Nonet (38 mm [1.47 in.]), MRSL TF15 (47 mm [1.85 in.]), BarRobusto (51 mm [2.01 in.]), Stetson II (51 mm [2.01 in.]), and Titanium 2 LS (51 mm [2.01 in.]) used the least water of the tall fescue group. Various factors resulted in limited data collection
in 2019 at the Amherst, MA, site (Approach 1), therefore they collected 2020 data using two distinct dry-down ‘seasons.’ Te first dry-down season of 2020 showed excellent entry differences under the rainout shelter with NAI-13-14 and PST-K11-118 Kentucky bluegrass requiring the least water to maintain green cover (8.7 mm [0.34 in.]). Other bluegrasses such as Everest, Babe, Midnight, and NAI-13-132 also finished in the top statistical group, surprisingly ahead of every tall fescue entry. Te second dry-down season delivered very similar water use numbers, but with much less statistical significance. NAI-13-14, PST-K11-118, Babe, and Everest needed the least water again in ‘Season 2’ but with several tall fescues performing equally well. Two sites, Logan, UT, and Fort Collins, CO,
collected 2020 data under the Approach 2 regime. In 2018 and 2019, no Kentucky bluegrass season average reached the acceptable lawn quality level at any ETo
level in Logan,
with many falling below even the minimally acceptable quality score for low maintenance (5.0). Tis trend continued in 2020, except a few bluegrass entries did finish with turf quality averages of at least 5.0. Under the 40 percent ETo
PST-K13-137 finished at 5.0 or 5.1 in turf quality. Under the 60 percent ETo
above 5.0, also with PST-K13-141 and PST-K11-118 (6.0). At 80 percent ETo
regime, Dauntless, NAI-13-14, and level, those same entries were at or , only PST-K13-141, Dauntless,
and NAI-13-14 finished above 5.0. Tall fescues again performed better overall than
Kentucky bluegrass at Logan as several entries maintained lawn turfgrass acceptable quality (6.0+) under 40 percent ETo
. Tall fescue entries Kingdom, Tor, and PST-5SDS finished with the highest turfgrass quality under the 40 percent ETo
replacement with season average turfgrass
quality scores of 6.6, 6.5, and 6.4 respectively. Also noteworthy is that the turf quality scores of those three tall fescue entries did not fall below acceptable (6.0) for any of the last eight weeks of the drought ‘season.’
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TPI Turf News July/August 2025
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