Perennial ryegrass

Perennial ryegrass (Lolium perenne L.; also called English ryegrass) is a temperate
(cool-season) perennial grass that is native to Europe, temperate Asia, and North Africa
(Jung et al., 1996; Balasko et al., 1995; Walton, 1983). It has been widely distributed to
other parts of the world, including North and South America, Europe, New Zealand, and
Australia. Both perennial and annual ryegrass (L. multiflorum; also called Italian ryegrass)
are important grasses in forage-livestock systems. Mixtures of the two species
sometimes are used to increase first season forage yields while establishing a perennial
grass stand (Cullen, 1964).

Perennial ryegrass is valued for high yield potential, fast establishment, reduced tillage
renovation applications, and use on heavy and waterlogged soils. High palatability and
digestibility make this species highly valued for use in dairy and sheep forage systems.
As a result, it often is the preferred forage grass in temperate regions of the world. In the
U.S., perennial ryegrass is used for forage predominately in the coastal northwest,
irrigated intermountain valleys of the west, the midwest, and northeast .

Description/Taxonomy

Perennial ryegrass is a temperate (cool-season) bunchgrass that can behave as an
annual, short-lived perennial, or perennial depending on environmental conditions
(Stefferud, 1948; Hall, 1992). It resembles annual ryegrass (Lolium multiflorum Lam.),
though the collar and blade of perennial ryegrass are more narrow and seeds are
awnless .

Vegetative Characteristics

Leaves of perennial ryegrass are folded in the bud (in contrast to annual ryegrass (Lolium
multiflorum L.) in which the leaves are rolled) (Francis, 1912; Nowosad et al., 1936;
Stefferud, 1948). Leaf blades are 2 to 6 mm (.08-.24 inches) wide, 5 to 15 cm (2-15
inches) long, sharply taper-pointed, and keeled. Blades are bright green, prominently
ridged on the adaxial (upper) surface, and smooth, glossy, and glabrous (hairless) on the
abaxial (lower) surface. Leaf margins are slightly scabrous (rough to the touch, covered
with minute serrations). Blades increase in size from the first to the seventh leaf on a tiller,
although tillers rarely have more than three live leaves at one time (Balasko et al., 1995).
Leaf sheaths usually are not keeled, compressed but sometimes almost cylindrical,
glabrous, pale green, and reddish at the base (Francis, 1912). Sheaths may be closed or
split. The collar is narrow, distinct, glabrous, and yellowish to whitish-green. Auricles are
small, soft, and claw-like. The ligule is thin-membranous, from 0.5 to 2.5 mm (.02-.1
inches), obtuse (rounded at the apex), and may be toothed near the apex (Nowosad et al.,
1936).

The shallow root system is highly branched and produces adventitious roots from the
basal nodes of tillers. Perennial ryegrass has no rhizomes or stolons. It will, however,
produce a dense and closely knit sward or turf with high plant densities and proper
management (Spedding and Diekmahns, 1972).

Reproductive Characteristics

Flowering stems (culms) are 30 to 100 cm (3 feet) in height depending on cultivar,
moisture, and site conditions (Hitchcock, 1950). The stem base commonly is reddish. The
spike-type inflorescence is up to 30 cm (12 inches) long, has 5 to 40 alternate, sessile
(bractless), awnless spikelets (in contrast to annual ryegrass which is awned) that are
positioned edgewise to the rachis (primary stem of the inflorescence). Spikelets contain 3
to 10 florets, with two glumes present in the terminal spikelet and with the inner glume
missing in the other spikelets.

Seeds of perennial ryegrass are awnless and range from 465,000 to 595,000 seeds per
kg (1,025,000-1,311,000 per lbs) (Effenberger, 1993). This compares with a range of
395,000 to 445,000 (871,000-981,000 per lbs) for annual ryegrass and an average of
338,000 seeds per kg (745,000 per lbs) for intermediate ryegrass. Perennial ryegrass
seed length is 5 to 8 mm (.2-.32 inches) and width at the midpoint is 1 to 1.5 mm (.04-.06
inches) (Spedding and Diekmahns, 1972).

Breeding and Development

There are many important perennial ryegrass cultivars and all are reproduced by seed.
Many types of ryegrasses exist because of self-incompatibility and crosses with other
Lolium and Festuca species (Riewe and Mondart, 1985). Persistence of perennial x
annual hybrids generally is intermediate between annual and perennial cultivars. As a
result, these crosses are called short-rotation ryegrasses.

There are both diploid and tetraploid forage-type cultivars. Tetraploids have fewer but
larger tillers with wider leaves, resulting in more open sods. Both the seed and seedlings
of tetraploids are larger, but growth rate following emergence is greater for diploids.
Tetraploids typically are less persistent than diploids (Balasko et al., 1995).

Cultivars

Including both forage and turf types, there are more than 100 perennial ryegrass cultivars
listed in the "Grass Varieties of the US" document (Alderson and Sharp, 1995). There are
more than 500 named cultivars are in the 1996 OECD list of cultivars (OECD, 1996).
Information on cultivars also is available from the Oregon Ryegrass Growers Seed
Commission and through the Germplasm Resources Information Network (GRIN; URL:
http://www.ars-grin.gov/).

Perennial ryegrass cultivars are grouped into three maturity categories; early,
intermediate, and late. This is helpful, but groupings are somewhat arbitrary, since
phenological development is a continuum and is affected by temperature and
photoperiod (Cooper, 1957; Silsbury, 1965). Thus, without common criteria and
standardized reporting procedures for maturity categories, there is substantial overlap.

Recommendations

Field trials for perennial ryegrass cultivar evaluation trials are conducted in various U.S.
and international research and extension centers. These trials include yield and/or quality
evaluation, based on local information needs. Consult your local Extension Service for
specific recommendations for cultivars that have performed well in your area.

Adaptation Area

Perennial ryegrass is best adapted to cool, moist climates (Hannaway and McGuire,
1981; Hall, 1992; Balasko et al., 1995; Jung et al., 1996). It grows well in early spring and
fall, but during the hot summer months it becomes dormant. Even with irrigation or
abundant summer rainfall, perennial ryegrass production suffers due to high temperature
stress when day temperatures exceed 30° C (86° F) and night temperatures exceed 25°
C (77° F). It is more sensitive to temperature extremes and drought than annual ryegrass.
Perennial ryegrass is less winter-hardy than orchardgrass (Dactylis glomerata L.) and tall
fescue (Festuca arundinacea Schreb.) and less drought tolerant than smooth
bromegrass (Bromus inermis Leyss). Studies in Wisconsin (Casler and Walgenbach;
1990; Novy et al., 1995), however, suggest that perennial ryegrass is able to survive
severe climates, even where snow cover is unreliable.

Optimum growth occurs between 20 and 25° C (68-77° F) (Spedding and Diekmahns,
1972). Perennial ryegrass grows best on fertile, well-drained soils but has a wide range of
soil adaptability. It is tolerant of poorly-drained soils and frequently is used in these
environments (Balasko et al., 1995). It tolerates both acid and alkaline soils, with a pH
range of approximately 5.0 to 8.3 (Cropper, 1996; Miller and Reetz, 1995; Hall, 1992).
Similar to tall fescue, perennial ryegrass is adapted to shade in the warmer portions of a
cool, humid climate where winter kill is not a problem (Beard, 1973).

In the U.S., primary adaptation and usage of perennial ryegrass for forage is in the Pacific
Northwest, though there is considerable use in irrigated intermountain valleys, the
midwest, and the northeast (Figure 1). Estimated perennial ryegrass forage production
was provided by Balasko et al. (1995) at 50,000 ha each for the Pacific Northwest and
northeastern areas. For the midwest, the estimate is 8,000 to 10,000 ha (20,000-25,000
acres) (S. Johnson, 1997, personal communication).

Perennial ryegrass is less persistent than other perennial temperate grass species such
as orchardgrass, tall fescue, timothy (Phleum pratense L.), smooth bromegrass, and
Kentucky bluegrass (Poa pratensis L.) (Balasko et al., 1995; Hall, 1992). Despite these
limitations, perennial ryegrass is the pasture grass of choice for areas with wet,
mild-temperate climates like the Pacific northwest and northeast U.S., Great Britain, and
New Zealand.

Management Establishment

In adapted areas, perennial ryegrass can be seeded in spring or late summer. In addition,
it may be fall-seeded in areas with mild winters. Seeding depth should be between 0.5
and 1.25 cm (0.25-0.5 inches) (Hall, 1992; Balasko et al., 1995). Recommended seeding
rates on a clean, well-prepared seedbed are 18 to 24 kg ha-š (15-20 lbs/a) in pure stands
and 12 to 18 kg ha-š (10-15 lbs/a) in mixtures with legumes. When seeding with a no-till
drill or surface seeding, seeding rates should be increased up to 45 kg ha-š (40 lbs/a) and
the existing sod should be mowed or grazed short to reduce competition (Fransen and
Chaney, 1996).

Fertility and pH Requirements

Perennial ryegrass requires high fertility levels for good production. Fertilization should be
based on a soil test. Perennial ryegrass will grow on soils with pH of 5 to 8, but forage
production is best at pH of 6 to 7 (Miller and Reetz, 1995). Consult your local Extension
Service for specific fertilization and liming rates (Hart et al., 1996a; Hall, 1992).

Perennial ryegrass is very responsive to N, with maximum yield attained between 600
and 1,200 kg N ha-š (535-1070 lbs N/a) per year (Whitehead, 1995; Morrison et al.,
1980). Typically there is an almost linear increase in yield of between 20 and 30 kg
(44-66 lbs) dry matter per kg N, until the rate of application is between 250 and 400 kg N
ha-š (223-356 lbs N/acre) per year. At higher rates, the response per kg of additional
fertilizer N declines until the maximum yield is attained.

Applications of total yearly N should be split as evenly as possibly to reflect the continuing
need for nitrogen throughout the growing season. The first application is provided at the
beginning of the season and the others after each harvest except the last (Whitehead,
1995; Wedin, 1974). This pattern of application produces a greater annual yield and
better quality forage than does a single, early spring application (Castle and Reid, 1968).

T-Sum 200

In mild climates, the initial N application can be made when pasture plants start to grow in
mid to late winter (Pirelli, 1996). Timing initial fertilization with the start of grass growth
has been assisted by using a thermal time method called T-Sum 200 (Kowalenko et al.,
1989). The first application of N is made when 200 heat units have accumulated. Heat
units are the average of high and low temperature in degrees C (maximum temperature
plus the minimum temperature divided by 2) summed beginning with January 1. (The
formula for converting Fahrenheit to centigrade is: degrees C = [(degrees F - 32) x
0.556]). Subsequent fertilizer applications are made following each grazing or mechanical
harvest.

Optimum Economic Rates

Typically, economical levels of annual N fertilizer rates have been suggested to be in the
range of 160 kg N ha-š yr-š (143 lbs N/a) (Balasko, 1995). However, economically
optimum rates of fertilizer application (the rate at which the marginal increase in the value
of the forage is equal to the marginal increase in the cost of fertilizer) can be estimated for
individual sites by developing a response curve which averages results over several
years. Although these are not precise estimates due to the variability of weather and
livestock systems, they can serve as a useful guide. In the United Kingdom a minimum
response of 5.7 kg DM per kg N was required for an economic return, whereas in the
Netherlands 7.5 kg dry matter (DM) per kg N was necessary (Whitehead, 1995; Reid,
1970, Prins et al., 1980; van der Meer and van Uum-van Lohuyzen, 1986). A different
approach, suggested by Morrison et al. (1980), determined the rate for producing a
marginal response was 10 kg DM per kg N. In England and Wales, this optimum rate
approach produced 90% of the maximum yield while using only 60% of the fertilizer.

A few studies have determined optimum N fertilizer rates based on milk or meat
production. This strategy calculates the optimum rate of nitrogen fertilizer based on the
price received for the milk or meat and the cost of fertilizer N (Whitehead, 1995; Gordon,
1974; Holmes, 1968). For milk production, this approach shows an almost linear increase
up to a fertilizer rate of 450 kg N ha-š yr-š (400 lbs N/a), with each kg N yielding about 15
kg (33 lbs) of milk (Whitehead, 1995). For beef production, targeting liveweight gain of
1,220 kg ha-š (1088 lbs/a) from fertilizer N rates of 300 kg N/ha (268 lbs N/a) per year
suggests that 2 kg (4.4 lbs) liveweight gain per kg of fertilizer N is attainable by young
animals (Whitehead, 1995; van Burg et al., 1981).

Legume Nitrogen Fixation

The amount of nitrogen fixed by legumes growing in combination with grasses depends
on the legume species and the environment in which it is growing (Joost, 1996). When
grown in the presence of available inorganic soil N, legume biological N2 fixation is
decreased (Heichel, 1985; Miller and Heichel, 1995). Fixation is decreased by reducing
the nitrogenase enzyme activity and by decreasing the formation of nodules (Eardly et al.,
1985; Shuler and Hannaway, 1993). In grass-legume mixtures, inorganic N also increases
the competition from the grass, which reduces N2 fixation per unit area.

High levels of N2 fixation rates per unit area of white clover-grass can be maintained only
under conditions of very low soil mineral N levels, which limit grass competitiveness (West
and Mallarino, 1996). Thus, white clover (Trifolium repens L.) - perennial ryegrass
communities dependent on symbiotic fixation as the N source are likely to be in chronic N
deficiency and below their potential for pasture yield potential (Ball and Crush, 1985).

The overall impact of applying fertilizer N to a well-managed grass and white clover sward
is to reduce N2 fixation. Moderate rates of N (up to 80 kg ha-š, 71 lbs/a) typically reduce
N2 fixation about one half (Whitehead, 1995; Cowling, 1982; Crush et al., 1982). Higher
rates (150-200 kg ha-š 133-178 lbs/a) are likely to eliminate N2 fixation entirely (Eardly et
al., 1985). The size of the effect is influenced by factors such as the time of year of
fertilizer application, the frequency of defoliation, soil moisture and other nutrients, and the
form of fertilizer N. Frequent defoliation minimizes the effect by reducing the competition
of the grass. In dry areas, irrigation can offset some of the effect, presumably by diluting
the inorganic nitrogen in the vicinity of the nodules, encouraging rapid growth, and
maintaining available energy supplies for fixation. Manure, urine, and less acid-forming
types of N fertilizer minimize decreases in N2 fixation (Moloney and Murphy, 1963; Murphy
et al., 1986).

Thus, accommodating the sometimes competing objectives of high yields, high quality
forage, optimizing N2 fixation by forage legumes, and maximizing the recycling of animal
manures and municipal biosolids requires a balancing of fertility requirements and
harvest/grazing management. Meeting but not exceeding soil, plant, and animal needs is
a continual adjustment process.

Developmental Physiology

In addition to defoliation height and plant energy reserves, regrowth of perennial grasses
is affected by its developmental physiology. The location and activity of meristems within
the grass canopy is very important. A large pool of active meristems is necessary to
capitalize on stored energy and current photosynthate to rapidly replace
photosynthesizing leaf area. The ontogeny (seasonal development) of a perennial grass
tiller can be divided into 4 growth periods; vegetative, elongation, reproductive, and seed
ripening (Moore et al., 1991). During vegetative development, leaf growth and
development occur. Stem internodes are differentiated but do not elongate. As long as
the tiller remains vegetative, leaves continue to be produced.

Reproductive growth (floral initiation) is triggered in vernalized tillers by exposure to
lengthening days during spring. Tiller internodes begin to elongate and raise the growing
point to a vulnerable height. Clipping or grazing below the growing point at the
early-jointing stage will cause tiller death (because there is no regrowth meristem) and
poor regrowth (because basal buds are not yet ready to re-initiate growth).

Management Implications

Defoliation management during vegetative growth should assure high quantities of high
quality forage and rapid regrowth. This can be achieved by allowing swards to attain a
height of 10 to 25 cm (4-10 inches) prior to grazing not shorter than 2.5 cm (1 inch) (6 cm
[2.4 inches] for mechanical harvest). When plants enter the reproductive growth phase of
internode elongation (early-jointing stage), defoliation management should avoid removal
of the elevated growing points until after heading. This will assure rapid regrowth of basal
buds forming new leaf producing tillers. Fertilization with N (50 kg ha-š, 45 lbs a-) following
each harvest cycle will assure rapid regrowth of leaves and roots.

Persistence

Cutting and grazing management affect stand persistence of many forage species,
including perennial ryegrass. Repeated harvesting without allowing replenishment of
storage carbohydrates will reduce stand persistence (Langer, 1990) and reduce regrowth
rates (Fulkerson and Slack, 1994). (Refer to the Defoliation section for a more complete
description of regrowth and persistence determinants.)

The presence of the fungal endophyte (Acremonium lolii Latch, Christensen & Samuels)
imparts insect resistance which improves persistence in some areas (Cunningham et al.,
1993). Toxic metabolites produced by the plant and endophyte in their symbiotic
relationship, however, cause animal health problems. (For a description of this problem,
refer to the Fungal Endophyte portion of the Animal Health/Forage Antiquality Issues
section.)

Frosted Forage

Perennial ryegrass is susceptible to temporary, and perhaps permanent damage if
utilized in freezing weather or when frosted (Balasko et al., 1995). Livestock (and human)
traffic should be prevented on frosted or frozen plants.

Conservation, Wildlife, and Turf Uses

Soil Conservation

Perennial ryegrass, like other grasses, is well suited to many different soil conservation
practices (CAST, 1986). Its extensive, shallow, fibrous root system makes it an effective
species for reducing surface soil erosion. Perennial ryegrass is recommended as a fast
starting component in mixtures, providing rapid cover and then allowing longer-lived or
more winter hardy species to become established [i.e. bentgrass (Agrostis stolonifera
L.), Canada bluegrass (Poa compressa L.), lovegrass (Erogrostis spp.), Kentucky
bluegrass, and fine fescues (Festuca spp.)]. In its adaptation range, perennial ryegrass
also is seeded alone to provide excellent soil erosion protection (Fransen and Chaney,
1996).

Turf

The "Green Industry," including home lawns and golf courses is estimated at over 20
billion dollars per year in the U.S. economy (Dubel, 1959). Use of perennial ryegrass for
turf has increased in recent years with selection of more dense and persistent turf types. It
is one of the most versatile of all turfgrass species. For turf, perennial ryegrass is used
alone or in combination with other grasses. Significant disease problems and limited cold
and heat tolerance, however, limit its persistence and zone of adaptation.

For the southern region of the U.S., perennial ryegrass's intolerance to high temperature
has become an advantage; it is used to overseed dormant bermudagrass (Cynodon
dactylon L.) on Southern lawns and sports fields during the winter months. The perennial
ryegrass thins and often dies during hot spring and summer weather, allowing the
transition to bermudagrass turf thus maintaining an active surface suitable for golf and
other sports (Beard, 1982).

Recent improvements in turf cultivars include improved disease resistance, high
temperature tolerance, and darker green color. European evaluation trials include
tolerance to close mowing and traffic (S.W. Johnson, 1996, personal communication).

One caution here for forage use, however, is that "turf-type" cultivars of perennial ryegrass
often have a fungal endophyte added for increased pest resistance and persistence
(Funk and Clarke, 1989). These endophyte-infected cultivars should be used with caution,
if at all, for livestock feed due to the presence of toxins (primarily lolitrim b and
ergovaline). (Refer to the Fungal Endophyte portion of the Animal Health/Forage
Antiquality Issues section.)

Diseases and Insect Pests

Diseases

In humid climates, perennial ryegrass is susceptible to ergot (Claviceps purpurea Tul.)
which is toxic to livestock and to stripe smut (Ustilago striiformis (West.) Niessl.) which
can cause grass to be unpalatable. Many cultivars are susceptible to leaf spots
(Drechslera spp.), fusarium (Fusarium spp.), brown blight (Drechslera siccans), and
other fungus diseases in hot, humid climates. Most varieties also are susceptible to snow
molds (Typhus spp., Fusarium spp., and Sclerotinia spp.) and many are susceptible to
mildews of various sorts including powdery mildew (Erysiphe graminis DC. Ex Merat.)
(Braverman et al., 1986).

In the northeastern and northwestern sections of the U.S., crown rust caused by Puccinia
coronata Corda, Stem rust caused by P. graminis subsp. graminicola Z. Urban, bacterial
wilt caused by Xanthomonas campestris pv. Graminis (Egli, Goto & Schmidt), and
Drechslera (Helminthosporium) spp. can be problems with perennial ryegrass
depending on weather conditions and cultivar susceptibility (Jung et al., 1996). Stem rust
often is a problem in late spring and early summer, especially if forage is allowed to
accumulate (S. Bittman, 1996, personal communication). Stem and crown rust occur in
late summer and early fall. Although rust is not toxic to livestock, it can affect palatability.
For horses especially, the spores from rusts and smuts can be a significant respiratory
problem. High fertility and harvesting the accumulated forage reduce rust problems. For
turf and grass seed production, chemical control measures are available (Pscheidt,
1996). Most, however, are not registered for forage use.

Insects

Grass grub (Costyletra spp.) is an important pest of ryegrass (Potter and Braman, 1991).
Grub larvae eat ryegrass roots, rendering the plant more susceptible to drought (Jung et
al., 1996).

In New Zealand, the Argentine stem weevil is a major perennial ryegrass problem
(Balasko et al., 1995). Perennial ryegrass is resistant to this weevil (and other pests) if the
grass is infected by the fungal endophyte (Popay et al., 1990). Presence of the
endophyte, however, is linked to the occurrence of a neurological disorder in livestock
known as ryegrass staggers. (Refer to the Fungal Endophyte portion of the Animal
health/Forage Antiquality Issues section.) For turf applications, the chinchbug and sod
webworm are additional pest problems (Fisher et al., 1996).

The European cranefly (Tipula paludosa) is of local importance in the Pacific Northwest
(Fisher et al., 1996). Chemical control measures are available (Table 3), but seldom
economical. Typically, pastures are reseeded with renovation techniques when stands
are lost to the European cranefly.

Seed Production

Oregon is the world's major producer of cool-season forage and turf grass seed. Mild and
moist winters with dry summers favoring seed development and harvest make the
Oregon's Willamette Valley an ideal place to produce high quality seed. This small region
produces almost two-thirds of the total U.S. seed production of cool-season grasses.
Nearly all of the perennial ryegrass seed in the U.S. is grown in Oregon.

In 1995, nearly 57000 ha of perennial ryegrass was harvested for seed in Oregon (Young,
1996). Average seed yield is 1300 to 1500 kg ha-š (1160-1338 lbs/a). Most seed
produced in the USA is of turf-type cultivars. Over 55 percent of Oregon's production of
perennial ryegrass was certified in 1995. Oregon produced 96 percent of all perennial
ryegrass acres applied for certification through the Association of Official Seed Certifying
Agencies in 1995 (AOSCA, 1995). The AOSCA summary reports total USA, Canada,
Argentina, and New Zealand certified production.

A vernalization period of low temperatures is necessary before photoperiodic (>13 h)
floral initiation for most perennial ryegrass cultivars (Silsbury, 1965). An obligate
vernalization requirement of at least 2 wk at 4°C (39.2°F) or lower was reported by
Cooper (1960). In contrast, Mediterranean types do not require cold temperatures and
initiate inflorescences at daylengths of 9 to 10 h (Balasko et al., 1995).

Perennial ryegrass produces seed once per year in late spring in the northeastern and
Pacific northwestern U.S. It is self-incompatible and will readily cross-pollinate (Balasko
et al., 1995).

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Document Citation

Evers, G.W., D.B. Hannaway, S. Griffith, S. Minier, P. Hoagland, M. Runyon, M.H. Hall, I.
Jacob, S.W. Johnson, E. Liss, S. Fransen, S.L. Fales, W. Lane, D.M. Ball, M. Chau, J.
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Ryegrass (Lolium perenne L.) International Forage Fact Sheet. Intl. Forage Species Fact
Sheet Series of the Forage Information System. URL:
http://www.forages.css.orst.edu/Topics/Species/Grasses/
Perennial_ryegrass/International_Fact_Sheet.html.