Perennial ryegrass on golf courses: Friend or foe?
The use of perennial ryegrass on golf courses has increased rapidly during the past several decades. This is due, in part, to its upright growth habit, tolerance to close mowing and the ease with which reel mowers can create striping on perennial ryegrass turf. However, perennial ryegrass has its drawbacks. Its environmental adaptations limit its geographic range, and gray leaf spot has recently become a serious disease problem. Is perennial ryegrass suitable for your course? That depends on your needs. Let's look at the pros and cons of ryegrasses on golf courses and some alternatives for when ryegrass isn't the best option.
Ryegrass types Two ryegrass species in the genus Lolium have important value in the fine turf market: L. perenne (perennial or English ryegrass) and L. multiflorum (annual or Italian ryegrass).
* Annual (Italian) ryegrass. Not to be confused with perennial ryegrass, annual ryegrass has lost some of its importance in recent years because it produces a coarser, more open turf than many newer turf-type perennial ryegrasses, and it is extremely susceptible to Pythium diseases. It also has lighter color than most perennial ryegrasses.
Annual ryegrass also has poor heat and cold tolerance. Like annual bluegrass, annual ryegrass quickly dies when a few warm days occur in early spring. This may result in thin spots where the permanent grass has not yet fully greened up.
However, annual ryegrass germinates quickly and is acceptable on fairways and general-use areas where color and appearance are not of greatest concern or when the budget is tight. Few improved turf-type cultivars of annual ryegrass are available. One that is available is Barverdi, while current forage-type cultivars include Astor, Gulf, Magnolia and Wimmera.
* Perennial ryegrass. Perennial ryegrass is a short-lived perennial originating from open areas and forest fringes of southern Europe and western Asia, extending as far south as northern Africa. Its first recorded use was in England in 1677 as a forage.
Several visible characteristics help distinguish annual ryegrass plants from perennial ryegrass. The overall appearance of the stands usually differ considerably-perennial ryegrass typically forms darker, more finely textured turf. This superior appearance is a major reason (but hardly the only one) it is preferred over its annual cousin.
Hybrids between annual and perennial ryegrass-called intermediate ryegrass (L. hybridum)-are in development for possible turfgrass use.
Pros of perennial ryegrass on golf courses Perennial ryegrass has a non-spreading, bunch-type growth habit with medium leaf texture, fairly high shoot density, good wear resistance and tolerance of soil compaction, quick establishment and bright green color (see Table 1, below). Plus, it tolerates lower mowing heights than Kentucky bluegrass or tall fescue.
Though courses sometimes grow it as a monoculture, perennial ryegrass in permanent turf successfully mixes with other cool-season turfgrasses such as Kentucky bluegrass to broaden a stand's resistance to diseases and other pests. For example, a mixed stand of Kentucky bluegrass and perennial ryegrass offers resistance to summer-patch diseases from which Kentucky bluegrass suffers, as well as gray leaf spot, a devastating disease of perennial ryegrass. Perennial ryegrass' texture, unlike that of bentgrass and tall fescue, is nicely compatible with that of Kentucky bluegrass.
Tolerance of low mowing is a distinct advantage of perennial ryegrass. Golf courses typically prefer fairway mowing heights under 1 inch, and tees are clipped even shorter. Plus, when mowed with a reel unit, perennial ryegrass easily acquires the striping that golfers enjoy seeing on fairways.
In addition to use as a permanent turf, perennial ryegrass is a common selection for overseeding dormant bermudagrass or zoysiagrass fairways, roughs and tees due to its rapid establishment and low cost. It provides attractive winter color and improves wear and traffic tolerance.
Rather than using pure ryegrass for overseeding, many superintendents mix perennial rye with Poa trivialis. This combination provides a better playing surface than either ryegrass or Poa trivialis alone. It also reduces seed costs-although perennial ryegrass is less expensive on a per-pound basis, you need to add only 1 or 2 pounds of Poa trivialis to 8 or 10 pounds of perennial rye to provide a solid stand. Compare this with the 15 to 20 pounds you'd have to use if you used perennial rye alone, and you can see where the savings occurs.
Greens are the most closely clipped turf on any course, and perennial ryegrass' tolerance of close mowing extends even down to green heights. That, along with its rapid establishment, is why perennial ryegrass has been (and still is) used for overseeding dormant bermudagrass greens. However, Poa trivialis is becoming more popular. It provides a better putting surface than perennial ryegrass. Plus, it requires little surface preparation, and its establishment rate is only slightly slower than perennial ryegrass', making it less disruptive during overseeding.
Perennial ryegrass' quick germination also makes it ideal for divot-repair mixes, as well as for rapidly providing cover on thinned or damaged areas.
Cons of perennial ryegrass on golf courses Perennial ryegrass is intolerant of drought and temperature extremes. Research indicates that 50 percent of a stand may be killed when soil temperatures at the 4-inch level fall to between 23 and 5 degrees F. In comparison, Kentucky bluegrass does not experience a similar level of kill until soil temperatures are between -6 and -22 degrees F. Bentgrass is even hardier, tolerating temperatures as low as -31 degrees F before experiencing this level of damage.
As most turf managers are well aware, perennial ryegrass languishes in hot summers, which limits its use in southern areas of the United States to winter overseeding. The newer cultivars-often selected for better year-round performance as permanent turf-tend to have somewhat better high-temperature tolerance. Unfortunately, this can be a drawback with overseeding because these cultivars tend to survive longer into summer, hindering the spring transition back to the permanent grass.
Pest problems historically have been slight to moderate with perennial ryegrass. The most notable diseases associated with perennial ryegrass are various rusts (Puccinia and others), brown patch (Rhizoctonia solani), Pythium, and leaf-spot problems caused by Drechslera (Helminthosporium) spp. These are normally easy to manage with proper cultural practices and prudent fungicide use.
Within the last several years, however, this has changed considerably with the widespread occurrence of gray leaf spot (or "blast") caused by Pyricularia grisea. This disease has become a major pathogen of ryegrass in many regions of the United States.
Gray leaf spot's spore-producing bodies literally explode, rapidly disseminating spores and causing widespread damage within a matter of days. Prolonged hot (80 to 90 degrees F), rainy, humid conditions favor this disease's development. Heavy morning dew and high overcast conditions also appear to promote this pathogen. Outbreaks are generally more severe in newly established turf, shady locations, turf heavily fertilized with nitrogen and areas with poor air movement.
Alternative choices With the recent upsurgence of gray leaf spot on ryegrass, many turfgrass managers are faced with replacing their turf with another cool-season grass. Unfortunately, no grass is perfect. Thus, changing from ryegrass to another turfgrass may reduce problems like gray leaf spot, but will also bring the inherent problems associated with the new choice.
In cool-humid and cool-arid regions, and northern portions of the warm-humid region, golf courses typically use cool-season grasses, alone or with other cultivars or species, for year-round color on fairways, roughs and out-of-play areas (see Table 2, below). Kentucky bluegrass, perennial ryegrass and fescues (tall and fine) are the primary choices for these cool-season courses. The traditional advice still holds true: mixes or blends are preferred because they reduce disease, insect and summer-stress problems. Some courses elect to use bentgrass for fairways, but typically as a monoculture and mostly at higher-budget facilities.
In the northern United States and in Canada, Kentucky bluegrass, bentgrass and fine fescues are the typical preferences because tall fescue and perennial ryegrass are less winter-hardy. Thus, the latter are more widely used in the mid-central regions of the United States, including the Transition Zone.
A recent trend in cooler regions has been to use predominantly pure perennial ryegrass in the Upper Transition and cool semiarid zones. However, as I mentioned previously, gray leaf spot has become a significant threat to perennial-ryegrass stands. In addition, some of these courses have experienced problems with winterkill. Superintendents try to overcome these problems by adding a small amount (for example, 20 to 30 percent) of Kentucky bluegrass, which has more recuperative ability due to its rhizomatous growth as well as greater cold tolerance. Unfortunately, perennial ryegrass may come to dominate mixed stands over time, but attention to seeding rates and cultivar selection can reduce this tendency. Some courses have switched entirely to bentgrass.
In the most northern regions, periodic winterkill is likely with perennial ryegrass and tall fescue. Thus, courses often avoid these species altogether, opting instead for Kentucky bluegrass alone on fairways. A blend of bluegrass cultivars is recommended for improved pest resistance, and bluegrass needs mowing above 1 inch for best turf growth and hardiness (though several seed suppliers market varieties that they contend will succeed at 0.5 inch).
Courses sometimes use fine fescues in the most northern areas, especially in shady or unirrigated areas, but these species tend to establish slowly and are susceptible to several diseases.
As I stated, there is no perfect turfgrass, and perennial ryegrass is no exception. Climate limits its use as a permanent turf to middle sections of the United States, and even there, gray leaf spot is forcing courses to consider other species-if not entirely then at least within a mixed stand. Nevertheless, ryegrass' advantages-its appearance, tolerance of traffic and low mowing, and rapid establishment-ensure it will remain a staple species for permanent stands and overseeded turf in southern areas. Each superintendent must evaluate the specific needs of his or her facility to determine where and when perennial ryegrass might be suitable.
Dr. Bert McCarty is professor of turfgrass science at Clemson University (Clemson, S.C.).
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