Annual Ryegrass (Lolium multiflorum Lam.)

Common Name: Annual Ryegrass

Scientific Name: Lolium multiflorum Lam.

Synonym: Lolium perenne L. ssp. multiflorum (Lam.) Husnot, Lolium multiflorum Lam. var. diminutum Mutel, Lolium multiflorum Lam. var. muticum DC., Lolium perenne L. var. aristatum Willd., Lolium perenne L. var. multiflorum (Lam.) Parnell

Family: Poaceae

Tribe: Poeae

Origin: Europe

Time of introduction:
During colonial times, exact date uncertain; late 1700s.


Annual ryegrass is a fast-growing, competitive winter annual cool-season grass grown nearly anywhere there is adequate available soil moisture. The inflorescence of annual ryegrass is a solitary spike with alternately arranged spikelets attached edgewise directly to the central axis. Leaf blades are bright green, rolled in the bud, and sharply taper-pointed. Annual ryegrass is used extensively as a cover crop, for erosion control and for short term forage production. It is tolerant of wet soils but not extensive periods of flooding. It is very useful as an interim crop between summer annual forage crops as row crops, between permanent pasture seedings, or for overseeding of warm season forages species. Tetraploid annual ryegrasses have good early spring production, are quite palatable, and tolerate a wide variety of soil conditions. Although somewhat less tolerant of severe and frequent defoliation than perennial ryegrass, annual ryegrass is relatively tolerant of defoliation as long as at least 2 to 3 inches (5 to 7 cm) of stubble remains after harvest, and regrowth periods are at least 3 weeks long. Annual ryegrass toxicosis is a disease of livestock caused by a group of highly toxic compounds called corynetoxins. They are produced only when annual ryegrass is infected with a specific nematode (Anguina agrostis), and only when that nematode is infected by a bacteria. Control of annual ryegrass toxicosis involves preventing nematode infection of the grass. Crop rotation, field burning, clipping immature seed heads, and fallowing are methods of reducing nematodes.

Life cycle (annual/biennial/perennial):
Annual, sometimes 1 1/2 years in mild winter climate areas. It can live 2-3 years in temperate areas of the Northwest.

Growth habit & Regrowth type:
Bunch-type, upright-growing grass. Culmed vegetative regrowth type.

Invasive potential:
Low when harvested before mature seed is produced; annual plant with no rhizomes or stolons. If allowed to produce seed, it can be a serious problem in winter small grain fields harvested for grain if annual ryegrass is in the crop rotation. It can produce too much green material for the combine cylinder to accept without clogging at times.

Typical use as an overseeding plant for warm-season pastures in the southeastern USA involves seeding in late autumn and completion of the life cycle the following spring. If managed for reseeding, livestock are removed when seed heads first appear.


Image Gallery: The OSU Forage Information System contains an Image Gallery that includes Annual Ryegrass photographs and drawings useful in identification. The URL for the gallery is:

The direct URL for Annual Ryegrass is:

Inflorescence: The inflorescence terminates the stem (culm). In annual ryegrass it is a solitary spike, 4 to 16 inches (10 to 40 cm), but typically about 12 inches (30 cm). It has 5 to 38 alternately arranged spikelets attached edgewise directly to the central axis (rachis). Annual ryegrass inflorescence image.

Spikelets: Annual ryegrass spikelets are 0.3 to 1.2 inches (8 to 30 mm) long, excluding awns, and contain 9 to 15 florets. Florets are 0.25 to 0.4 inch (6 to 10 mm) attached to the rachilla. The terminal spikelet has two glumes. The inner glume is absent in the other spikelets. Annual ryegrass spikelets image.

Seed: A seed is a mature ovule enclosed by a lemma and a palea. The lemma, the lower bract, is 0.15 to 0.3 inch (4 to 8 mm) long, with a straight, slender awn up to 0.6 inch (15 mm). The rachilla segment is somewhat wedge shaped. Seeds per pound average 228,000 (502,000 per kg), with a range of 200,000 to 250,000 (440,000 to 550,000 per kg). Annual ryegrass seed image.

Stem: Stems (culms) are comprised of nodes and internodes. Each node bears a leaf. The uppermost culm segment is called the peduncle, the structure that supports the inflorescence. Annual ryegrass culms are 12 to 40 inches (30 to 100 cm) tall depending on variety, moisture, and site conditions. The stem base of annual ryegrass commonly is pale green or yellowish. Annual ryegrass stem image.

Leaf: Leaf blades of annual ryegrass are rolled in the bud (in contrast to those of perennial ryegrass, which are folded). Leaf blades are 0.15 to 0.4 inch wide (4 to 10 mm) and 2.5 to 8 inches long (6 to 20 cm). They are sharply taper-pointed and keeled.

Blades are bright green. They are prominently ridged on the upper surface. Lower surfaces are smooth, glossy, and hairless, with a prominent midrib. Leaf margins are slightly rough to the touch. The blade is joined to the sheath at the collar, a zone of meristematic tissue. The leaf sheath is split and overlapping, with no hairs. Annual ryegrass clasping auricles and leaf blades.

Collar: The collar region is a narrow band of meristematic tissue accounting for increasing blade length. Once the leaf has achieved its maximum length, cells in the collar cease dividing. In annual ryegrass this region is narrow, hairless, and yellowish- to whitish-green. The 0.04 to 0.16 inch (1 to 4 mm) ligule is membranous. Auricles are narrow and hairless. Annual ryegrass collar image.

Root: The root system of annual ryegrass is highly branched and dense, with many fibrous, adventitious roots. Annual ryegrass has no rhizomes or stolons. Annual ryegrass root system.

Physiology and growth period:
Annual ryegrass, as a cool-season grass has C-3 physiology and anatomy. Ryegrass seedlings have the greatest rate of growth in spring among cultivated cool-season grasses. This feature gives ryegrass an effective competitive edge in crop or pasture establishment.

Cultivars exhibit a wide range of winterhardiness. The mechanism(s) of cold tolerance needed for southern latitudes in the USA may be different than those needed for northern latitudes. It does not become dormant in winter in the Deep South, and therefore active tillers must tolerate rapid shifts in temperature over a short time span.

Soil N status is the largest single nutrient factor affecting annual ryegrass growth and development.

Among Lolium species, there is a continuous gradient of floral induction requirements. These range from obligate to facultative requirement for short-days (8 hr) or low temperatures 32-37 F (0-3 C) or both, to no environmental stimulus required. Usually daylength-temperature floral induction is associated with perennial ryegrass, whereas annual types require only genetic induction. Some references indicate a greater than 11 hour daylight requirement for flowering.

Quality/anti-quality factors:
Annual ryegrass produces high quality forage as pasture, greenchop, silage, or hay: stems are larger than those of perennial ryegrass, so quality declines as maturity advances.

Annual ryegrass toxicosis
Annual ryegrass toxicosis is a disease of livestock caused by a group of highly toxic compounds called corynetoxins. They are produced only when annual ryegrass is infected with a specific nematode (Anguina agrostis), and only when that nematode is infected by a bacteria (Clavibacter toxicus), and only when the bacteria is infected by a bacteriophage. Infection can be recognized as a yellow slime on annual ryegrass seed heads.

The toxins produced by this complex combination of infections affect the nervous system, and their effects become most obvious when animals are stressed or excited. Symptoms include neurological disturbances, a high-stepping gait, incoordination, and convulsions. The condition can cause extensive brain damage or death.

Annual ryegrass toxicity has been a problem mainly in Australia and South Africa. Although the disease was reported many years ago (1961) in Oregon, it has not been observed recently because of the widespread use of open field burning to dispose of grass straw and stubble.

Control of annual ryegrass toxicosis involves preventing nematode infection of the grass. Crop rotation, field burning, clipping immature seed heads, and fallowing are methods of reducing nematodes.

Perennial ryegrass staggers
Perennial ryegrass staggers is a disorder of animals grazing perennial ryegrass pastures. The causative agents are compounds called tremorgens, the most important of which is the alkaloid lolitrem B produced by the endophytic fungus Neotyphodium lolii(previously known as Acremonium lolii Latch). This fungus has been found in some annual ryegrass varieties. No significant animal health problems, however, have been associated with the use of annual ryegrass as forage in the United States.



Annual ryegrass has moderate tolerances to heat, cold, poorly drained soils, and low pH, so it is often used as a quick source of high quality forage during parts of the growing season that match its tolerances.

In the milder regions of its adaptation zone, annual ryegrass can survive for several years. In the more extreme environments (including high summer temperatures and very low winter temperatures), it behaves as an annual. Annual ryegrass is not highly winter hardy or drought tolerant, but is adapted to a wide range of soils and will tolerate low fertility and poor drainage.

Suitability zones:
In the United States, annual ryegrass can grow nearly anywhere there is adequate available soil moisture. The largest area of annual ryegrass forage production is from eastern Texas and Oklahoma to the Atlantic Coast, and from the Gulf Coast north to the transition zone of warm- and cool-season species. In this area, it is used as a winter annual forage crop, often overseeded into bermudagrass and bahiagrass pastures. It also is an important species along the Pacific coast where rainfall exceeds 20 inches (500 mm), and in the Southwest, where it is grown under irrigation.

In addition to use in the United States, annual ryegrass is an important forage species in Ireland, the United Kingdom, Europe, central Mexico, Australia, New Zealand, China, and South America.



Quantitiative Table:

Max Temp (C)
Min Temp (C)
Precip (mm)
Soil pH Soil Drainage
Soil Salinity
Low High Low High Low High Low High Low High Low High
Well Adapted 24 34 -5 8 675 9999 6.0 7.5 MWD MWD 0 2
Moderate 22 35 -5.5 7 625 9999 5.5 8.0 SPD MWD 0 4
Marginal 20 35.5 -6 6 575 9999 5.0 8.5 PD WD 0 8
1. For the High values for January Minimum temperature and Annual Precipitation: "9999 is entered to indicate no limit to the high values for this tolerance category."
2. For Soil Drainage categories, " Abbreviations are used for Soil Drainage categories: VPD (very poorly drained), PD (poorly drained), SPD (somewhat poorly drained), MWD (moderately well drained), WD (well drained), SED (somewhat excessively drained), ED (excessively drained)."

Climate: Lack of cold tolerance limits fall planting areas to zones with minimum January temperatures of >14 F (>-10 C). Annual ryegrass is best adapted to cool, moist climates. Best growth occurs between 68 and 77 F (20 to 25C). Thus, annual ryegrass grows well in early spring and fall. Although it is more tolerant of heat than perennial ryegrass, temperature stress causes summer production to suffer even if adequate water is available. Upper temperature growth limit is approximately 90 F (30 C). It is well-adapted to areas with an annual precipitation rate of at least 27 inches (700 mm), but can survive in areas with as low as 19 inches (500 mm) of annual precipitation.

Soils: Annual ryegrass grows best on fertile, well-drained soils, but has a wide range of soil adaptability. It is grouped with forages that prefer high soil moisture conditions, being suited to well drained to poorly drained soils. Annual ryegrass is tolerant of long periods of continuous flooding - 15 to 20 days when temperatures are below 81 F (27 C). It is tolerant of acidic to alkaline soils (pH 5.0 to 7.8). Below pH 5.0, aluminum toxicity may be a problem. Higher pH can cause chlorosis due to iron and manganese deficiencies. It is best adapted to soils with a salinity level of 0 to 2 mmhos/cm, but may survive in areas with up to 8 mmhos/cm.

Grazing Management: Although somewhat less tolerant of severe and frequent defoliation than perennial ryegrass, annual ryegrass is relatively tolerant of defoliation as long as at least 2 to 3 inches (5 to 8 cm) of stubble remains after harvest, and regrowth periods are at least 3 weeks long. This suggests a range of appropriate defoliation management schemes, ideally including a rest period provided by rotational grazing, or hay/silage harvesting. Management to promote rapid recovery following defoliation should focus on harvesting prior to heading. This will ensure high-quality forage and trigger retillering at a somewhat earlier date.

Turf Management: Used as a short duration turf plant, disappearing within a year.

Pests: Diseases: Leaf diseases reduce forage quality and overall nutritive value of the forage. Most recent varieties of annual ryegrass are resistant to crown rust, once the major disease problem. Leaf spot, barley yellow dwarf virus, and blast cause minor problems.

Although rust is not toxic to livestock, it can affect palatability. For horses especially, the spores from rusts and smuts can cause significant respiratory problems. High fertility and harvesting the accumulated forage reduce rust problems.

For turf and grass seed production, chemical control measures are available. Most, however, are not registered for forage use.

Pests: Insects: No insect problems are unique to annual ryegrass. Grass grub is an important pest of ryegrass in most areas. In the southeastern United States, annual ryegrass seedlings are attacked by mole crickets and fall armyworms.

The European cranefly (Tipula paludosa Meigen) is important in some parts of the Pacific Northwest. Chemical control measures are available, but seldom economical. Typically, pastures are renovated and reseeded when stands are lost to the European cranefly.

Pests: Nematodes: Annual ryegrass has no particular susceptibility to nematodes.


Two primary types are distinguished, Italian and Westerwold types. Italian types have a vernalization requirment for flowering, Westerwold types do not.

Two types of annual ryegrass cultivars are recognized: tetraploid and diploid types. Tetraploids are faster to germinate, have wider leaves, and typically higher yields. Diploids, however, are longer lived and may combine better with other species.

See the Forage Information System variety database for a listing and descriptions based on the "Grass Varieties in the United States" publication.


Annual ryegrass is probably the fastest emerging forage grass anywhere in the United States. It germinates well (in 6 to 10 days) when daytime temperatures range from 50 to 80 F (10 to 27 C). In mild winter climates, such as west of the Cascade Mountains in the Pacific Northwest, you can seed annual ryegrass from late August to early October. Late August seedings may require irrigation to get seedlings started before the fall rains. Spring-seed in February, March, or April.

Seeding rate:
For overseeding warm-season grasses in the Southeast, seeding rates are 30 to 35 lb/a (34 to 39 kg/ha) when seeded alone and 20 to 25 lb/a (22 to 28 kg/ha) when mixed with small grains.

With poor seedbed preparation, increase seeding rates by 50 to 100 percent. For renovation, the existing sod should be mowed or grazed short to reduce competition.

Seeding depth:
Seeding depth should be between 0.25 and 0.5 inch (0.6 to 1.3 cm).

Fertilization and liming:
Annual ryegrass responds to high soil nutrient levels. Fertilization should be based on a soil test. Consult your county extension office for specific fertilization and liming rates.

Yield responses to N fertilization are greatest if the N is applied and available at the time the crop makes its most rapid growth. For annual ryegrass, that period usually is late spring (April and May in the Pacific Northwest). Annual ryegrass yields generally have increased with N application rates to as high as 400 lb N per acre (448 kg N/ha), when applied in multiple applications of 75 to 100 lb N/a (84 to 112 kg N/ha) following each harvest.


There are nearly 3 million acres of annual ryegrass in the United States, with about 90 percent used for winter pasture in the Southeast. About 80 percent of this ryegrass pasture is established by over-seeding into warm-season perennial grasses to extend the grazing season. Annual ryegrass also is grown for silage and hay on poorly drained soils where small grains are not adapted.

Seed crop:
Oregon leads the nation in annual ryegrass seed production, producing nearly 97% of the total. Over 190 million pounds was harvested in the 2003-2003 crop year.

Annual ryegrass produces some of the highest quality pasture that can be grown in the southeastern United States. Pastures are used for stocker cattle, replacement heifers, and lactating dairy cows, as well plantings made for other types of grazing animals, including deer.

Its strong seedling vigor, high yield, and high quality also make it valued for temporary pastures in the coastal Northwest. Although annual ryegrass grows quickly and is highly productive, its short-lived and aggressive nature make it less desirable in cool season permanent pasture mixes.

Silage and hay
Annual ryegrass often is harvested for silage. The high production capacity of this grass makes it popular for additional feed when short hay supplies are expected.

Harvesting annual ryegrass for hay is not recommended in high rainfall/humidity areas. Good hay-curing weather typically occurs too late in these regions for producing high-quality ryegrass hay.

Erosion Control/Conservation:
Annual ryegrass is well suited to soil conservation uses. Its extensive, shallow, fibrous root system makes it effective for reducing soil erosion. It can be used alone for temporary cover or as a small (5 percent of the total weight), fast-starting component in mixtures, where it provides rapid cover and allows longer-lived or more winter-hardy species to become established.

Manure and biosolids application
As a high-yielding grass with high growth rates, annual ryegrass is able to absorb large amounts of nitrogen (N) from manure and biosolids application. Efficient utilization of this N, however, requires that rates and timing be appropriate for the climatic conditions. Research has shown that 400 lb (448 kg) of N can be accounted for in harvested forage. Care should be used in determining application rates of manure or biosolids, because only 30 to 40 percent of their N is available the first year. About 50 percent of the remaining organic nitrogen becomes available in each subsequent year. If subsequent applications are not reduced, excessive amounts of nutrients may be available to forage crops, leading to animal health problems.

Wildlife habitat and feed:
Annual ryegrass is an excellent wildlife feed. Forage provides high-quality grazing and a quick source of energy for geese, coots, widgeons and other ducks, wild turkeys, rabbits, deer, and elk.

In the northern United States and Canada, annual ryegrass is grown as a summer annual turf plant, typically as a quick cover in advance of longer-duration turf grasses.

Economic value:

Nearly all of the annual ryegrass seed production is from Oregon. Approximately 120,000 acres produce a seed yield of 220 million pounds, with a farmgate value of $44 million. Wholesale value is $55 million and retail value is $77 million.

More than 1 million hectares (approximately 2.5 million acres) of annual ryegrass pastures are used in the southeastern USA. With about 52% of the beef cow herd located in 13 to 14 southeastern states, sustainable, high quality forage for pasture, hay, and/or silage are necessary for economic survival of these related industries.

The annual ryegrass forage value can be estimated by multiplying an average yield (4 tons per acre) times the estimated value of each ton of dry matter ($75 per ton) times the acreage (2.5 million acres). This yields an estimated value of $750 million.

Soil and water conservation:
"Green accounting" is difficult; what is the value of conserving a pound of topsoil or filtering the water from agricultural lands prior to entry in streams, rivers, and lakes? Extensive use of annual ryegrass as a construction site quick covering plant contribute significantly to soil and water conservation.

Annual ryegrass is used for overseeding lawns and golf courses in southern regions of the USA. This value is contained within the value for the seed sold and the aesthetic value and quality of life improvement resulting from more beautiful turf.


  1. California Exotic Pest Plant Council. 1999. Exotic Plant Pest List. California Exotic Pest Plant Council. California. Available at (verified 12 July 2004).
  2. Hannaway, D.B., et al. 1999. Annual ryegrass (Lolium multiflorum Lam.). PNW Extentension Pub. 501. Oregon State University. Corvallis, Oregon. Available at (verified 12 July 2004).
  3. Jacques, D. 2002. The identification of certain native and naturalized grasses by their vegetative characters. Canadian Agriculture Library (CAL) [Online]. Available at (verifed 12 July 2004).
  4. Rouquette, F.M. Jr. and L.R. Nelson. (Eds.) 1997. Ecology, Production, and Management of Lolium for Forage in the USA. Crop Science Society of America Special Pub. No. 24. CSSA, Madison, Wisconsin.
  5. USDA NRCS Plants Database [Online]. 2004. Italien ryegrass. Available at (verifed 12 July 2004).
  6. US Forest Service Web Segment [Online]. 2004. Lolium multiflorum. Available at (verifed 12 July 2004).
  7. Young, W.C. III. 2004. Oregon Grass and Legume Seed Crops Preliminary Estimates, 2003. Department of Crop and Soil Science, Oregon State University. Corvallis. Available at (verifed 8 July 2004).

David B. Hannaway, Christina Larson, and Dan Myers, Oregon State University
Marc Cool, Barenbrug - USA

Document creation:
4 June 2004

Last update:
13 August 2004

Don Ball, Auburn University
Carrol Chambliss, University of Florida
James B. Cropper, Natural Resource Conservation Service (NRCS)
Marty Chaney, Natural Resource Conservation Service (NRCS)
Steve Johnson, DLF-International Seed Co. (Not yet contacted)

Review date:
9 June 2004 (Ball)
22 June 2004 (Cropper)
7 July 2004 (Chambliss)
7 July 2004 (Chaney)