Warm-season grasses for dummies - part 1

Transcription

1 Warm-season grasses for dummies - part 1 What is the difference between warm and cool-season grass? This is the first in a two-part series on warmseason management for golf courses. This article focuses on the differences between the major warm-season grasses that are available in Europe. By: Megan Z. Hood B.Appl.Sci(Hons). RIPTA. Turfgrass Agronomist, STRI Ltd Bermuda seadling 34

2 Warm season It is important to understand that the differences between warm-season and cool-season grasses does not just relate to the fact that warm-season grasses are best adapted to warmer areas than cool-season grasses. The easiest way to discriminate between the cool and warm-season grasses is to classify them by their photosynthetic efficiency. Warm-season grasses begin the process of carbohydrate production with a four-carbon compound, whereas the cool-season grasses use a three-carbon compound. This is why we call warm-season grasses C4 (carbon-4) grasses and cool-season grasses C3 (carbon-3) grasses (Jones, 1985). Warm- Season Grasses Cool-Season Grasses Common Name Latin Name Common Name Latin Name Bermudagrass Hybrids Cyndoon dactylon Annual meadowgrass Poa annua x C. transvaalensis Buffalograss (Buchloe) Buchloe dactyloides Browntop Agrostis capillaris (Colonial bentgrass) Kikuyu Pennisetum Chewings fescue Festuca rubra L. clandestinum ssp commutata Seashore Paspalum Paspalum Creeping bentgrass Agrostis stolonifera L. vaginatum There are also visible differences in the cell structure of warm and cool-season grasses at a microscopic level (Christians, 2004). This article will focus however on the practical difference between warm and cool-season grasses. These include: St Augustine Grass Stenotaphrum Creeping red fescue Festuca rubra secundatum Zoysia Zoysia matrella Hard fescue Festuca longifolia Kentucky bluegrass Poa pratensis Rooting warm-season grasses usually have a deeper root system (which will survive and grow even in very hot conditions) Water-use Cool-season grasses have a high water requirement than warm-season grasses. In warm weather the cool-season grasses must leave their stomates open longer than warmseason grasses to capture CO2 (which results in water being lost more readily). Shade-tolerance Warm-season grasses generally require full sunlight in order to photosynthesise, whereas some cool-season grasses require only ¼ to ½ full sunlight to photosynthesise. Cold Tolerance Warm-season grasses will go dormant or even die in cool conditions. The warm-season grasses vary in their susceptibility to the cold, so cold tolerance is an important selection factor in many situations (particularly transition zones). Table 1: Classification of warm and cool-season grasses. Perennial ryegrass Sheep fescue Slender creeping red fescue Strong creeping red fescue Tall Fescue Velvet bentgrass Lolium perenne Festuca ovina Festuca rubra, spp. litoralis Festuca rubra. spp. rubra Festuca arundinacea Agrostis canina Which grasses are cool or warm-season grasses? Some cool-season grasses perform reasonably well in transition zone areas and can, with careful management, tolerate hot and humid climates. This is why we often see certain cool-season grasses confused with their warm-season counterparts. Probably the most commonly confused grass within this group is creeping bentgrass, which will perform well in warm climates but is actually a cool-season grass. The following table lists important turf species. Cutting greens Paspalum 35

3 Warm season The three main types of warm-season grass grown in Europe are: Bermudagrass hybrids (Cynodon dactylon x C. transvaalensis) Kikuyu Seashore paspalum Bermudagrass Hybrids (Cynodon dactylon x C. transvaalensis) Whilst common Bermuda (Cynodon dactylon), is still seen on some golf fairways in Europe, the hybrid Bermudagrasses (Cynodon dactylon x C. transvaalensis ) have been the standard for putting green surfaces for around 30 years. In the late 1990s, ultradwarf Bermudagrasses were introduced for putting greens in Europe and have become increasingly popular, e.g. Champion, Tifeagle etc. With higher shoot densities and finer leaf texture than earlier hybrids such as TifDwarf, these provide better overall quality and compare favourably with creeping bentgrass surfaces. Bermuda grass Reproduction Whilst hybrid Bermudagrasses are generally only propagated through vegetative means (stolons and/ or rhizomes), some improved seeded varieties are now available (e.g. Princess). The seeded varieties can be useful on remote sites, sites where vehicle access is an issue and where formal cultivation i.e. sprigging is not possible due to play and high usage pressures. Management Hybrid bermudagrass New sowing rate: 5g/m2 to 10g/m2 Stolonising rate: 5kg/100m2 to 20kg/100m2 Mowing heights: 2-5mm (greens) 7-30mm (other areas) Zoysia Positive attributes of hybrid Bermudagrass include: Can provide an excellent playing surface for greens, tees and fairways with sound management. Ultradwarfs respond well to light rolling for increased speed without resorting to very low mowing heights. Very good wear tolerance and recovery. Establishes rapidly under good growing conditions. Cultivars are now available for propagation by seed and vegetative material. Tolerates being irrigated with recycled or grey water but, if such sources are used, a regular programme of leaching to maintain an acceptable level of salts is necessary. This will, 36

4 clearly, increase the quantity of water required even if it is of a quality unsuitable for drinking compared to seashore paspalum. Limitations of hybrid Bermudagrass include: Susceptible to common turfgrass pests and diseases. Accumulates thatch very quickly, even during the grow-in period. Sensitive to shade and requires at least eight hours of full sunlight each day to maintain good turf quality. Dysplasla disorder (Grain/ nap) can be an issue (can be managed with regular use of static and/or rotary brushes). Swirling grain is much more difficult to control and is caused by tremendous horizontal growth tendencies of the ultradwarf Bermudagrass. The ultradwarf grasses can be maintained periodically at very low mowing heights, but they become stressed during periods of prolonged cloudy, hot and humid weather. Bermudagrasses generally enter dormancy before Kikuyu, but after the seashore paspalums (soil temperatures below C). The new ultradwarf varieties can retain some colour at lower temperatures. The tan colour of dormant grass is an issue, particularly at resort venues where winter golf is a priority. Wear needs to be controlled during the dormancy period unless overseeding is under taken. Struggles to compete with other warm-season grasses, particularly Kikuyu. Bermudagrass can be a very challenging rough grass as its density means that it can be very difficult to extract a golf ball from the rough (can lead to slow play and lost balls). General required maintenance input is high fertilsation etc Historically little research-based information has been available, however significant progress has been made in recent years (Barton et al, 2005). Whilst Kikuyu s coarse leaf prevents it from being of use on greens, its ability to tolerate cooler weather means that it is the logical choice for the fairways and tees on many courses in transition zones. Whilst Kikuyu will survive in infertile conditions, for best performance as a turfgrass, Kikuyu requires moderate-high soil fertility, with nitrogen applications scheduled over the warmer months of the year. Growth Habit Both fertile and male-sterile types are common in Europe. Male sterile Kikuyu does not produce stamens (i.e. male flower parts). Fertile strains produce stamens over the summer period. Traditionally, the male sterile Kikuyu strains have been of superior quality to the fertile strains. Management - Kikuyu New sowing rate: 1g/m2 to 2g/m2 Stolonising rate: 5kg/100m2 to 15kg/100m2 Mowing heights: 8-40mm Positive attributes of Kikuyu include: Grows well in some areas in which other warm-season grasses struggle to survive. Longer growing season in transitional areas than Bermudagrass or seashore paspalum. Kikuyu is susceptible to heavy frost and the exposed foliage is quickly desiccated brown. However, recovery generally quickly occurs and the turf will green up a few days following the frost assuming that conditions are favourable. Very tolerant of most insect pests and is rarely affected by diseases. Very few broadleaf weeds are capable of competing against the Kikuyu when good growing conditions are provided. Kikuyu has good wear tolerance (only moderate growth and recovery in cool conditions in some areas). Quick, easy and inexpensive to establish through the planting of stolons. With good maintenance practices can provide a good quality surface for tees and fairways. Well-suited to overseeding with cool-season species such as ryegrass. Texture of leaf, unless well managed through grooming practices, can be very coarse at fairway and approach heights of cut in comparison to Bermuda species. Limitations of Kikuyu include: Even under intensive mowing the leaf is too coarse for use on golf greens or where a fine textured turf is desired. Kikuyu use is usually limited to fairways, tees or sportsfields. The vigorous growth of Kikuyu means that ingression into areas such as green surrounds Kikuyu (Pennisetum clandestinum) Kikuyu originates in Africa on highland plateau regions at elevation levels of m and is named after the dominant tribe in its area of origin. Kikuyu is well adapted to a mild, humid climate that receives regular rainfall (or irrigation). Of the warm season grass family Kikuyu has the greatest capacity to maintain active growth during cool periods. Kikuyu is very well suited to many areas in Europe and is a very popular choice in Australasia. It is very often chosen as a landscape grass and cross contaminates golf course turf from surrounding urbanised areas. Poa Annua 37

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6 Warm season and bunkers is a common problem. Some chemicals have been shown to successfully remove Kikuyu from both warm and coolseason swards. Kikuyu usually responds well to plant growth regulators. Kikuyu is not suitable for use in long rough (over 125mm) as it is very difficult to extract the ball out of and golf balls are difficult to find. Kikuyu is not suitable for use on heavy clay soils or very wet areas, but it will adapt with ease. Kikuyu will not tolerate extremely hot or dry conditions without irrigation. Frequent mowing is required over periods of active growth, this occurs at any time over the warmer months of the year when soil moisture is not limiting. A lax mowing programme will result in a sod-bound, spongy turf. Heavy mowers are needed as light units ride upon the thatch increasing the effective mowing height. Kikuyu produces seed culms 1-2 hours directly after mowing that will reduce aesthetic and playing performances for most areas of turf. Seashore Paspalum (Paspalum vaginatum) Whilst seashore paspalum has been used on golf courses since the 1950s, they have not traditionally been used on golf greens because the varieties available were of inferior quality to the other available grasses (Carrow and Duncan, 1999). Major advances in the development of seashore paspalum since the early 1990s have led to the introduction of several fine-textured varieties, which are proving to be very popular in warm climates. Seashore paspalum is a warm-season perennial grass that readily spreads via rhizomes and stolons. Traditionally seashore paspalum has been propagated by rhizomes and stolons, however in recent years seeded varieties suitable for golf greens have become available (e.g. Seaspray was released in 2005). One of the outstanding characteristics of seashore paspalum is its salt tolerance. It is considered to be the most salt-tolerant of the warm-season grasses (Carrow and Duncan, 1998). With irrigation water quality and availability at the forefront of environmental/golf development concerns, the breeding of such grasses is having a major impact. Other positive attributes of seashore paspalum include: Tolerates a wide variety of mowing heights so the same grass can be used on tees, fairways, greens and roughs, eliminating the problem of cross-contamination of areas, which is common in the warm-season situation. Produces a dense cover and tight canopy on tees, fairways and rough, often providing a superior lie to Bermudagrass or Kikuyu at higher mowing heights. Deep root system (even at low mowing heights) Very good drought tolerance (if a good root system is present). Nitrogen requirements on established turf are 30-50% lower than hybrid Bermudagrasses. Tolerant of some shading/ smog cover (Carrow & Duncan, 1999). Recovers quickly from divots/ disturbance (reducing weed ingression and improving the appearance of the turf area). Information on the management of seashore paspalum is widely available. Will compete more effectively against warm season weed grasses than Bermudagrass. Limitations of seashore paspalum include: Susceptible to common turfgrass pests and diseases. Not tolerant of heavy frost. Leaves and stems are tough, requiring sharp mowers to produce a clean cut. Wear on mowers is higher than cool-season grasses. Can suffer from Dysplasla disorder, grain and heavy scalping. Good quality water is required for optimal establishment. Has a markedly higher water requirement than Bermudagrass. Accelerated thatch accumulation due to its highly rhizomatous growth habit. Wear needs to be controlled during the dormancy period unless overseeding is undertaken. Excessive growth, which can cause mower scalping that is slow to recover. Aggressive topdressing is required to manage thatch and to produce a smooth, firm surface. Management Seashore Paspalum New sowing rate: 5g/m2 to 7g/m2 Stolonising rate: 5kg/100m2 to 20kg/100m2 Mowing heights: 3-5mm (greens) 7-40mm (other areas) References: Carrow, R.N and Duncan, R.R Salt-affected Turfgrass Sites: Assessment and Management. Ann Arbor Press, Chelsea, MI. Carrow, R.N and Duncan, R.R Seashore Paspalum The Environmental Turfgrass. John Wiley & Sons, New York, pp Jones, C. A C4 Grasses and Cereals: Growth, Development, and Stress Response. John Wiley & Sons, New York, pp About the Author: Megan Hood (megan.hood@stri.co.uk) works as a regional agronomist with STRI. Megan has worked in Australasia, the Pacific Islands, Asia and Europe and specialises in the management of both warm and cool-season golf courses. 39