Key Takeaways

• Warm-season grasses are often mentioned for their drought tolerance and ability to help courses save water, but there are significant differences in the water requirements among species and cultivars. 

• In this study, bermudagrass generally exhibited higher drought tolerance than zoysiagrass or buffalograss, and newer cultivars such as ‘TifTuf’ and ‘Tahoma 31’ showed improved drought resistance compared to older bermudagrass cultivars such as ‘Tifway’.

• ‘Meyer’ zoysiagrass required more water than improved zoysiagrass varieties to maintain acceptable turf quality in simulated drought conditions and newer zoysiagrass cultivars had higher turf quality ratings under a typical irrigation regime (60% replacement of evapotranspiration).

• Buffalograss required similar amounts of water as the other two species to provide acceptable turf quality under a rain-out shelter, but when placed under comparable irrigation regimes in the field, buffalograss quality declined more rapidly. This limitation was likely due to the variability in climate of each site, relatively short mowing height and management conditions in the trial.  

• The response of turfgrass species to drought varied depending on the local climate and cultivar. Prior to selecting a grass, it’s essential for golf courses to establish test plots to evaluate species and cultivars for multiple seasons in their unique growing environment and under their desired irrigation regime.

Eleven cultivars of bermudagrass, four cultivars of zoysiagrass and two cultivars of buffalograss were evaluated. The trials were maintained in a consistent manner across locations, following standard growing recommendations for the region. Each study was established in the local soil type, with no sand capping and no sand topdressing applied. Plots were maintained at 0.5 inch, a typical golf course fairway mowing height, and other stresses were minimized.

Study Approach 1: Individually Irrigated Turf Plots Under a Rain-Out Shelter

Materials and Methods

Four locations were chosen to conduct the rain-out shelter study: Jay, Florida; Griffin, Georgia; Starkville, Mississippi; and Stillwater, Oklahoma. During the first year, plots 3 feet by 3 feet were established from seeds or plugs (seeded cultivars noted in Table 2). At the beginning of the summer in years two, three, and four of the study, turfgrass plots received a uniform amount of irrigation; thereafter, water replacement was suspended and data collection began.

During the acute drought imposition, turfgrasses were evaluated regularly (either daily, biweekly or weekly) according to the irrigation needs in each region. When the turfgrass quality of a specific cultivar was below acceptable, estimated when the plot reached a level of 65% wilt coverage determined by digital image analysis, the turf was hand watered with a volume of water necessary to return the plot to an acceptable percent wilt and turf quality level. Each plot that required hand watering and the amount applied was then recorded. The dry-down period lasted from 21 to 113 days (Table 1) after which normal irrigation resumed and recovery was measured.

Key Results 

The results for each cultivar in the trial were averaged over the four study locations and are presented in Table 2 as inches of water needed daily to maintain acceptable turf quality. Notable results are summarized below: 

• The bermudagrass cultivars ‘TifTuf’ and ‘Tahoma 31’ were consistently the top-performing cultivars and required the least irrigation water to maintain acceptable turf quality.

• Among zoysiagrass cultivars, the experimental variety ‘FAES 1306’ required the least amount of water. The older cultivar ‘Meyer’ had the highest water requirement of all cultivars. 

• The buffalograss cultivars ‘Cody’ and ‘Prestige’ generally performed in a range between the other two species. 

• The highest water requirement came from bermudagrass cultivars ‘PremierPRO’ and ‘Dog Tuff’.

• In Florida, five bermudagrass cultivars and one zoysiagrass cultivar did not require irrigation and in Oklahoma, three bermudagrass cultivars did not require irrigation. We could attribute this to plant genetic improvement, local environmental conditions and soil type.

• In Mississippi, zoysiagrass required more than twice the amount of irrigation compared to most of the bermudagrass and buffalograss cultivars. 

Study Approach 2: Three Levels of ET-Based Irrigation

Materials and Methods

Approach 2 required a larger area than Approach 1 with three different ET-based irrigation levels scheduled in separate sections. Each section of turf was either hand watered or a sprinkler system was installed to provide one of three levels of irrigation. Each study was set up with three replications for each ET level. The locations reporting data were Riverside, California; Las Cruces, New Mexico; College Station, Texas; and Fort Lauderdale, Florida. Buffalograss did not survive the climatic conditions at the Fort Lauderdale location as indicated with blank cells in Table 3. 

The first year was used to establish the turf. Years two through four were used to impose the chronic drought treatments. Each plot at each site had irrigation set at one of three levels: 60% replacement of ET (considered an adequate amount of water for warm-season turf), 45% replacement of ET or 30% replacement of ET. Depending on the location, irrigation was applied one or three times per week for between 121 to 148 days. In case of a rain event, irrigation was withheld, and the amount of precipitation was subtracted from the next irrigation event. 

Key Results

Results for each trial location are shown in Table 3 as average turfgrass quality rated on a 1 to 9 scale – with 1 being poor, 6 or above being acceptable, and 9 being perfect – for each cultivar under the three different irrigation regimes. With significant environmental variability, turfgrasses performed differently at each location, hence the importance of trials in many regions across the U.S. Below are summaries of the results by cultivar and location:

• Averaged over locations, ‘TifTuf’ bermudagrass was the best-performing cultivar of any grass, maintaining an average quality of 6.5 under the 30% ET irrigation regime. ‘Tifway’ (6.0 quality) and ‘Tahoma 31’ (5.8 quality) were the two following best cultivars at that irrigation level. 

• No buffalograss or zoysiagrass cultivars maintained acceptable quality under the 30% ET irrigation regime when averaged across locations (excluding Florida). The best two zoysiagrass cultivars were ‘CitraZoy and ‘Stellar’ with an average quality of 5.5.

• No cultivar of any species maintained acceptable quality at the 30% ET regime in Riverside, California, but ‘TifTuf’ had acceptable quality (6.2 quality) at the 45% ET-replacement irrigation regime.

• In the high desert environment of Las Cruces, New Mexico, ‘TifTuf’, ‘Tahoma 31’, and ‘Tifway’ maintained acceptable quality at the 30% ET regime. Further, all zoysiagrass cultivars had acceptable quality at all ET-regime levels. Buffalograss was among the worst performers, even at the 60% ET regime, most likely due to factors including the fairway maintenance regime, less-than-ideal climate and prolonged drought. 

• In College Station, Texas, trends were similar among the top-performing zoysiagrass and bermudagrass cultivars as in other locations. However, the two buffalograss cultivars ‘Prestige’ and ‘Cody’ had above-acceptable turf quality across all irrigation regimes, even at 30% ET replacement. Considering all trial locations, Central Texas may have been best suited for buffalograss maintained at fairway height.

• In Fort Lauderdale, Florida, turf quality was acceptable for nearly all irrigation regimes and cultivars, and differences among cultivars were minimal, despite the study being run in their driest season.  

Conclusion

This study demonstrates that there are important differences in water requirements among warm-season grasses – both old and new – depending on the species, cultivar and location for use. If you are planning to establish warm-season grasses at your course and water use is a consideration, establish a trial of multiple options a few years before you renovate and see how different species and cultivars perform at your site under your planned maintenance program.

For superintendents wondering whether zoysiagrass or new bermudagrass cultivars perform better in drought conditions, this study suggests that the answer depends on where you are. Although buffalograss only produced acceptable turfgrass quality in College Station, Texas, it’s worth noting that trial conditions were not conducive to maintaining buffalograss at fairway height whereas previous research has shown it can produce high-quality fairways given the right conditions (Frank et al., 2004). 

The USGA and NTEP thank all the turfgrass research scientists and their supporting teams who conducted trials at several locations over multiple years. Comprehensive data from all study locations and years for this trial are available from NTEP.

Dr. Matteo Serena is the senior manager of irrigation research and services for the USGA Green Section and can be reached at mserena@usga.org.

References

Frank, K.W., Gaussoin, R.E., Riordan, T.P., Shearman, R.C., Fry, J.D., Miltner, E.D., & Johnson, P.G. (2004). Nitrogen rate and mowing height effects on turf-type buffalograss. Crop Science, 44, 1615-1621.