Selecting bermudagrass cultivars-now and in the future
Selecting a bermudagrass cultivar has become more complex in recent years. Numerous cultivars are available, and suppliers tend to promote each as the "best." So how do you decide which is best for your site? Although I can't select the cultivar for you, I can help you make a more informed decision.
Bermudagrass is a cosmopolitan grass adapted to a broad range of environmental conditions. However, broad variability exists among cultivars (see Table 1, page 22) and their ability to produce the desired quality turf for specific uses (golf-course greens and fairways, athletic fields, lawns, landscapes, roadsides, parks, etc).
Bermudagrass displays many advantages: * A variety of cultivars are available, providing a range of choices of turf qualities. * It is relatively easy to establish. * It is hardy. * It grows quickly. * It is broadly adapted. * It tolerates traffic.
But bermudagrass also has its limitations. It can tolerate only a limited amount of shade and wet soil; it requires frequent mowing to prevent scalping; and it requires relatively high levels of nitrogen to produce good quality turf. (However, in our research at Tifton, Ga., we are selecting hybrids that have potential to produce good quality turf with lower levels of nitrogen.)
Considerations when selecting a cultivar Most cultivars on the market have one or more characteristics that someone felt would be useful or that they could use to market the grass. I suspect that every commercial cultivar has looked good to someone at some location. The question you have to ask is, "Which cultivar do I need at my location and for my use?" We frequently hear and see descriptions such as "greener," "better quality," "deeper roots," and "more resistant to.." The questions you should ask are: "Compared to what?" and "Where is the data?"
Beautiful pictures, observations and testimonials are okay, but to make an informed decision, you must have good, replicated scientific data from tests that use established cultivars as a control. Evaluate the data. You can obtain these data from the institution that developed or released the cultivar or others that have tested the cultivar (such as the National Turfgrass Evaluation Program, or NTEP-see "To obtain NTEP reports.," page 24).
Remember that you cannot find solutions to all the weaknesses or potential problems of a cultivar. However, data should exist to support the claims that suppliers make for a cultivar. Below are questions that you should ask about how and where the cultivar was tested:
* Has it been tested in my area or at least at my latitude? Comparing northern-latitude plantings with more southern plantings is probably more informative than comparing eastern vs. western plantings because the former can affect such things as cold resistance and seed-head production, while the latter may not.
* How long has it been tested? This is extremely important for perennial grasses such as bermudagrass. Cultivars respond differently to conditions such as continuous mowing, traffic, alternating seasons (growth and dormancy) and pests over time. I cannot overemphasize the importance of testing a cultivar in permanently established plots for several years, especially because it is not a general practice to replant bermudagrass every year.
* How have successful (and unsuccessful) growers managed the cultivar? Considerations include such factors as planting date, soil conditions, fertility, mowing height and frequency and traffic. For example, a cultivar may be cold-resistant, but if you plant it in late summer or fall without adequate time to establish a root system, it could experience winterkill. Mowing height also can greatly affect winter survival and turf quality, as can fertility and traffic.
Common types vs. triploid hybrids When people refer to a "hybrid" bermudagrass, they usually are referring to a triploid interspecific hybrid (involving two distinct species) with 27 chromosomes. (All species have a typical number of chromosomes that constitute one complete set of genetic material. Some plants, especially types created by breeders, contain multiple whole sets of chromosomes. A triploid, or 3x, hybrid possesses three complete sets of chromosomes rather than one, which is why it is called triploid (3 x 9 = 27).) These triploid hybrids do not produce pollen or seed and depend on vegetative propagation such as with stolons and rhizomes. Vegetative propagation makes a uniform turf possible. Also, because of the lack of pollen production by these triploid hybrids, people who suffer from pollen allergies are not affected when they are around these grasses. Examples of triploid bermudagrass cultivars can be found in Table 2, at right.
Common bermudagrass usually has 36 chromosomes (Tifton 10 is an exception and has 54 chromosomes) and can produce seed and pollen. Seed production makes it simpler to propagate and plant the cultivar. However, a stand of a seeded cultivar can produce a mosaic appearance over time because each plant is genetically different (see Table 3, page 24, for a list of seeded varieties).
Some common bermuda-grass cultivars are single-plant types that are commercially marketed because of unique characteristics. Examples are Tifton 10, Quickstand, FloraTex and Vamont (see Table 2). These cultivars are vegetatively propagated and will produce a uniform turf like the triploids, but usually with lower visual quality because of their coarser texture. Although these cultivars produce pollen, they usually do not set much seed unless they receive pollen from another (different) bermudagrass type in the surrounding area.
Available commercial cultivars The number of new, commercially available bermudagrass cultivars has greatly increased. Fourteen of the 20 vegetatively propagated cultivars listed in Table 2 have been commercialized in the last 10 years. Eighteen seeded cultivars are listed for the 1997 National (NTEP) Bermudagrass Test. Vegetatively propagated cultivars seem to display larger differences than do the seeded cultivars. Among the seeded commercially available cultivars, Princess has the finest texture and produces the highest-quality turf.
The "fine" triploid or 3x cultivar group in Table 2 consists of varieties that mainly are used for greens. The super dwarfs (sd) are much finer-textured than the other cultivars in the group and are relatively new to the turf industry. They require more management, but the reward is a superior putting surface.
The 3x cultivars in the "coarser" group are slightly coarser-textured, but still produce superior-quality turf at a mowing height of 0.5 to 1.0 inch, depending on the cultivar. Most of the cultivars in this group produce a denser, more wear-resistant sod than common bermudagrass. The Tif cultivars probably have the finest texture in this group.
The tetraploid, or 4x, group in Table 2 is basically composed of selected common-bermudagrass types that have one or more characteristics that make them desirable. For example, Quickstand has good cold resistance. Even though these cultivars are common bermudagrass types and produce pollen, they produce little, if any, seed because it usually takes two or more different plant types growing together to produce seed in bermudagrass. They have to be vegetatively propagated to maintain the identity and purity of the cultivar.
Future cultivars Cultivar selection will become more complex in the future because the "shopping list" of desirable traits will grow. The visibility of the turf industry has generated greater interest in cultivar development and marketing. Five basic types of new cultivars will be produced:
* New triploid hybrids. Production of triploid hybrids with new genetics will be important for the high-quality-turf industry. They will broaden genetic diversity, which should ensure a supply of viable cultivars in the event a particular variety becomes susceptible to a serious pest. New hybrids should reduce management inputs for pesticides because genetic resistance to mole crickets and other insects, diseases and nematodes will be "built" into the cultivar. Resistances to cold, shade, drought and salt also are being incorporated into new hybrids.
* Mutant offtypes from current triploid hybrids. Natural mutations in some of the triploid cultivars such as Tifdwarf probably will continue to occur. Although most mutations do not improve the cultivar, an occasional mutation may add a beneficial trait such as dwarfness. However, using too many of these mutants from a particular cultivar increases the chances of a large portion of the turf industry being negatively affected (usually referred to as genetic vulnerability) if that cultivar becomes susceptible to a pest or disease. Selecting new mutated types from an unstable cultivar (one that readily mutates) usually results in basically the same cultivar with one new characteristic. However, individuals will continue to select these natural mutants and market them.
* Triploid hybrids improved by molecular techniques. We will see more of these cultivars in the future, especially with characteristics such as resistance to herbicides and insects. The turf industry should take care that these genes are added to several cultivars so that a large portion of turf is not planted to the same cultivar with only minor gene changes.
* Vegetatively propagated common selections. Someone sees a common type that looks good at some location. They collect some, increase it and market it. No advantage really exists with these types (compared with seeded common types) unless the plant type has a unique characteristic that could be lost if it goes through a seed generation.
* Seeded common bermudagrass. In general, few textural differences exist in commercial seeded cultivars. However, future seeded cultivars will have finer texture to produce a denser turf that you can mow shorter. Because a stand of a seeded cultivar is made up of many different plant types, the appearance of a common-bermudagrass stand can change over time due to environmental conditions, mowing height and pests-factors that may favor some bermudagrass types more than others.
The outlook for new bermudagrass cultivars is positive. More locations have scientific breeding programs, and more people are making selections. Some cultivars will be significantly better than the current ones on the market. It will be up to you to evaluate the scientific data comparing the new cultivars with those currently on the market.
Wayne W. Hanna is a research geneticist at the U.S. Department of Agriculture's Agricultural Research Service Coastal Plain Experiment Station (Tifton, Ga.).
A great deal of NTEP variety information is readily available on-line through the NTEP website located at www.ntep.org. However, you also can request NTEP reports by writing to: National Turfgrass Evaluation Program Beltsville Agricultural Research Center-West Building 002, Room 013 Beltsville, MD 20705
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