Zoysiagrass Water Relations

All zoysiagrasses have the same drought resistance, don't they? Such a generalization existed when the cultivar ‘Meyer’ was released in the United States. As new varieties entered the market, our thinking changed about how zoysiagrasses respond to their environment. Response to drought resistance differs greatly among genotypes currently on the market or in evaluation for introduction as future cultivars.

The zoysiagrass genus actually encompasses several species, each exhibiting variation in leaf texture (width), color, density, rate of spread, and tolerance to heat, shade and supplemental irrigation. Although classified as a warm-season turfgrass, some zoysiagrass species survive cooler climates exposed to sub-freezing temperatures and snow cover.

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Numerous studies evaluated zoysiagrass reaction to water stress. These studies rated plants visually (green color retention, percent of cover, turf wilt and stress recovery) as well as physiologically (relative water content of leaves as measured by a number of devices). Descriptions of commercially-available cultivars, including their relative responses to restricted irrigation are provided in Table 1, above.

TAES-DALLAS WATER STRESS EVALUATIONS

Researchers at Texas A&M Research and Extension Center, Dallas, assessed several zoysiagrasses using a configuration known as a linear gradient irrigation system. It functions by distributing decreasing amounts of supplemental irrigation as the distance from the central irrigation line increases. Plots nearest the central line received enough water to essentially maintain field capacity (fully watered). Outer plots received no supplemental irrigation.

During one phase of studies, researchers grouped zoysiagrass genotypes into low, medium and high levels of drought resistance. Although coarser (wider)-leaved cultivars tend to remain green the longest during a drought, some fine and medium-textured experimental genotypes demonstrated lower water requirements. Since this study concluded, one genotype (Diamond) was released as a cultivar from this group.

Further experiments compared supplemental water requirements to prevent water stress and also to maintain acceptable turf. Turf wilt and green color-loss ratings distinguished zoysiagrass genotypes. These genotypes were visually grouped into four classes (see Table 2, above), based on leaf length and width.

Researchers noted considerable variation in water requirements. El Toro, Emerald, FC13521 and a number of experimental lines (including Crowne and Palisades, subsequently released as cultivars) maintained acceptable ground cover without supplemental irrigation. Relating to leaf type, long, wide-leaved and long, narrow-leaved zoysiagrass types generally had greater ground cover, although exceptions existed within each class.

When irrigation was supplied to plots, FC13521 and Emerald used the most water, while El Toro used the least water. Crowne and Palisades also required among the lowest amount of supplemental irrigation. Meyer and Korean Common water requirements were intermediate among the group of zoyisagrasses.

Interestingly, Emerald and FC13521 required greater supplemental irrigation to prevent water stress, yet they also maintained an acceptable ground cover where no supplemental irrigation was provided. These results suggest a contradiction. There may be some type of survival mechanism allowing them to maintain acceptable turf coverage where no supplemental irrigation was supplied, even while they used more water to remain actively growing when water was freely supplied.

El Toro, Crowne and Palisades required 48 percent of the irrigation water necessary to maintain Meyer in an acceptable condition, and 67 percent of the water required to maintain Emerald and FC13521.

Greenhouse experiments measured water content levels among 15 zoysiagrasses in comparison to survival and recovery from stress. Under these conditions, Crowne, El Toro and Palisades recovered most after stress, and required the least irrigation. Physiological responses correlated with stress recovery. This means new cultivars may be developed using physiological measures to screen new material for drought resistance.

OTHER WATER USE STUDIES

Georgia research demonstrated variation in wilt among zoysiagrass cultivars during a moderately severe dry-down period. Cultivars performing best included El Toro, Crowne and Diamond. Meyer and Emerald wilted more severely under the same conditions.

Texas A&M University research in College Station determined moderate dehydration avoidance in the zoysiagrass cultivars FC13521, followed by Diamond. During shoot recovery, FC13521, Diamond and Meyer were superior to Emerald, El Toro, Korean Common and Belair.

WHERE DO WE STAND WITH ZOYSIAGRASS WATER USE?

Cultivars released since the introduction of Meyer zoysiagrass demonstrate wide-ranging responses to supplemental irrigation. A number of cultivars in the studies described tolerate minimal to no supplemental irrigation. This group generally includes types with wider leaves.

Additional cultivars, not included in these experiments, are currently commercially available and may also exhibit superior drought resistance. Producers of these cultivars may have such information available for their respective materials. As cultivars continue to be introduced, you may expect this drought response range to expand, particularly with regard to thriving under reduced watering.

Bridget Ruemmele, Ph.D., is a turfgrass specialist who lives in Rhode Island.

Table 1.
CHARACTERISTICS OF SOME COMMERCIALLY-AVAILABLE ZOYSIAGRASS CULTIVARS
Cultivar Physical description Adaptation Relative responses to restricted irrigation
Belair Medium - coarse leaf width; dark green color; relatively rapid spread rate; less dense than Meyer Home lawns: Mows relatively easy for a zoysiagrass Shoot recovery after drought is poorer than Meyer
Cashmere Narrow leaf width; rapid lateral growth Fair shade tolerance; tolerates low mowing; low winter hardiness High water use
Cavalier Narrow leaf width; low rhizome, high stolon production Salt and shade tolerant; multiple uses, including lawns, athletic fields, and golf fairways; more winter hardy than Diamond Intermediate recovery rate
Crowne Medium to coarse leaf width; rapid spread rate Good winter hardiness and shade tolerance Low water use; good shoot recovery after water stress
Diamond Narrow leaf width; high rhizome and tiller production Highly salt and shade tolerant; withstands close mowing as on tees and greens; rapid recovery from injury Moderate to good dehydration avoidance
El Toro Medium to coarse leaf width; light green color High heat tolerance; moderate shade tolerance Low water use; Shoot recovery after drought is poorer than Meyer in one experiment, but rated good in another
Emerald Narrower leaves than Meyer; non-fluffy dark green, dense growth Shade tolerant; fair to good winter hardiness High water use; shoot recovery after drought is poorer than Meyer
FC13521 Narrower leaves than Meyer High water use; moderate dehydration avoidance; good shoot recovery after stress
Korean Common Variable — usually medium to coarse leaf widths More variable than other cultivars since this is the only one listed grown from seed Intermediate water use; shoot recovery after drought is poorer than Meyer
Meyer Medium to coarse leaf width; slower to establish than more recent cultivars Good winter hardiness Intermediate water use; good shoot recovery after stress
Palisades Medium to coarse leaf width; rapid regrowth Good winter hardiness and shade tolerance; tolerates low mowing Low water use; good shoot recovery after water stress

Table 2.
ZOYSIAGRASS CULTIVARS CLASSIFIED BY LEAF TYPE
Leaf type Cultivars
Short, narrow Cashmere, Diamond
Short, wide Meyer
Long, narrow Emerald, FC13521, Cavalier
Long, wide El Toro, Korean Common, Palisades, Crowne

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