Annual ryegrass

Lolium rigidum Gaudin

Family: Poaceae.

Names:

Lolium is from the Greek word for craft, deceitful or treacherous because Darnel (Lolium temulentum) can be toxic and it was believed to be a changed form of wheat.
Annual Ryegrass

Other names:

Wimmera Ryegrass
Merredin Ryegrass

Summary:

Annual Ryegrass is a palatable annual pasture grass. It has a narrow inflorescence of numerous small spikelets, 4-18 mm long, which are arranged alternately up the inflorescence. The leaves are shiny on one side and dull on the other. Native to the Mediterranean, Annual Ryegrass is a widespread weed of roadsides, bushland, crops and pastures and flowers in spring. Seed heads can be infected with Annual Ryegrass toxicity and/or an Ergot that makes them toxic to animals.

Description:

Cotyledons:

One.

Leaves:

Parallel veins. Emerging leaf folded flat in the bud. Often has a red dot at the inside base of the tillers.
Blade - Dark green, 30-150 mm long, 0.5-5 mm wide. Shiny on under side, ribbed on the upper side. Virtually hairless.
Ligule - Membranous, flat topped or rounded, 1.5 mm long.
Auricles - Variable from long to small and shrivelled.
Sheath - Green or purplish, split to the base but looks fused initially and becoming loose with age. Hairless.

Stems:

Tufted, 100-1200 mm tall, erect, stiff, round and hollow with solid nodes. Often have a reddish tinge and purple on the nodes and at the base. Hairless. Sometime bent at the lower nodes. Flattened where seed spikelets alternate up the stem. Occasional roots at the lower nodes especially in wet conditions.
Tillers profusely and becomes prostrate under grazing. All stems produce seed heads.

Flower head:

At the ends of stems. Slender, rigid, straight or slightly curved spike like panicle. 30-300 mm long. 2-20 spikelets are set into hollows alternately on either side of the wavy stem. Main axis rough to touch. Spikelets tend to stay closer to the stem at maturity than in other Ryegrass species.

Flowers:

Spikelets - Parallel sided, flattened, 5-18 mm long. Sunken into the flower stem at maturity. Without stalks. Awnless or rarely awned. 2-13 flowered often with one empty.
Florets - Lance shaped, bisexual.
Glumes - Outer one is about the same length as spikelets and held close to the stem enclosing the spikelet. First glume, against the stalk, is small except in terminal spikelet. Second glume 5-20 mm long, rounded on the back, thick, 3-9 nerved but usually 5-7 nerved, narrowly egg shaped.
Lemma - Spear shaped, rounded on the back, 3-10 mm long, 3-5 nerved. Tip translucent with tiny hairs. Without awns normally or if present usually 1-1.5 mm long.
Palea - Similar to lemma, keel with tiny teeth.
Awns - Usually awnless or less than 10 mm long.
Stamens -
Anthers -
Breaks above the glumes and between the florets.

Seeds:

Covered with a stiff outer husk. Brown to yellow or greyish. Cylindrical to oval, 5-7 mm long x 1-2 mm wide. Surface grooved, ridged, hairless. 2-3 mg per seed with an average of 2.8 mg. Seeds tend to remain attached to the stem until mechanically dislodged.

Roots:

Large fibrous root system.

Key Characters:

Florets lance shaped, not swollen in fruit. Lemmas awnless and more or less round tipped. Glume more than 10 mm long and as long or longer than the spikelet. Grain linear-oblong.
Virtually hairless.
Often has a red dot at the inside base of the tillers.
Emerging leaf folded flat in the bud.
Variable auricles.
Membranous ligule.
Leaves shiny on one side.

Biology:

Life cycle:

Annual grass. 75-80% of the seed will germinate on the first or second significant autumn rain. 12-23% of seed germinates after June (McGowan, 1970). Spike initiation occurs after a cold requirement has been satisfied and the day length increases to more than 8 hours. This results in relatively uniform flowering in late-winter/spring. About 5% of the seed carries over into the following season.
Ecotypes from different areas can have quite different rates of development. The time taken to spike emergence correlates with the length of the growing season (Gill, 1996).
The rate of development increases as day length increases.

Reproduction:

By seed. Wind pollinated. Outcrossing. Diploid (2n=14)

Flowering times:

Spring to early summer in western NSW.
October to March in SA.
September to November in Perth.
Spring and summer in WA.
Flowering can occur over photoperiods of 8-24 hours, however there is a vernalisation requirement for flowering which tends to synchronise flowering in the field.

Seed Biology and Germination:

1000 seed weight is 2-3 g with an average of 2.8 g.
Seed banks take 3-5 years to run down to low levels when seed set is prevented.
Seed has an after ripening period of about 8 weeks, but little dormancy. 7-22% of seed have dark dormancy and won't germinate until they have been exposed to light.
Seeds generally prefer to germinate in dark conditions.
Dormant seed that is hydrated in light remains dormant. Dormant seed that is hydrated in the dark loses its dormancy and will germinate readily if returned to light conditions. That is, the dormant portion of the seed bank has a requirement for darkness during hydration and a requirement for light for germination (437).
Seed that is still attached to the seed head is less likely to germinate than those that have been dislodged and in contact with the soil. In cereal stubbles up to 20% of the seed may still be attached to the stem. In swathed crops it is much less.
On non wetting soils, conditions suitable for germination may not occur and this results in carry over of seed from one year to the next.
Optimum germination occurs from seeds buried 20 mm deep under field conditions. No seed germinates if buried greater than 100 mm deep, but they will germinate if returned to the surface layers.
The optimum temperature for germination in the light is 270C and 110C for germination in the dark. The low temperature optima of buried seeds limits germination after summer rainfall events.
In the field, temperature and light are relatively unimportant in determining germination levels.
Tillage affects the germination pattern. Generally cultivation increases the speed and quantity of emergence but the opposite is occasionally reported. There may be greater Annual Ryegrass seed carry over into the following season in undisturbed (zero tillage) areas.
A single wetting and drying of the seed increases the speed of subsequent germination of Annual Ryegrass seeds. After a dry summer, more of the seed is likely to germinate after planting of the crop.

Vegetative Propagules:

Vegetative Propagules: Occasionally forms roots at the nodes of the stems that are in contact with the ground.

Hybrids:

Wind pollinated and readily forms hybrids with other ryegrass species.
Many ecotypes. Subspecies rigidum has herbaceous glumes shorter than the spikelet. Subspecies lepturoides has indurate glumes longer than the spikelets.
Cultivar Merredin flowers 10-14 days earlier than Cultivar Wimmera.

Allelopathy:

Annual Ryegrass that is infected by Rust fungus produces substances that inhibit the growth of White clover and other plants. (Scott Matner).

Population Dynamics and Dispersal:

Seed productions of 31,000-45,000 seeds/m2 were recorded in an irrigated wheat crop (Rerkasem et al 1980). and 20,000 seed/m2 in a pasture (Gramshaw, 1972) Plants surviving herbicide treatments usually set seed and Davidson (1990) recorded 2500-9000 seeds/m2 being produced from survivors of herbicide treatments.
A good stand will produce about a 1000 kg/ha of seed.
Most spread was from intentional planting and the distribution of hay.
Spread by seed.
40-80% of seed produces seedlings at the break of the season and the rest normally germinate in several waves over winter and early spring.
Annual Ryegrass plants that germinate 3 days before wheat is 5-8 times more competitive than those that germinate at the same time as the crop and over 10-20 times more competitive than those that germinate 3 days after the wheat (Moore 1979).
Cultivation
Annual Ryegrass seed banks tend to decline fastest in uncultivated areas or mouldboard ploughed areas. Tyne or disc cultivated areas tend to maintain Annual Ryegrass infestations.
On heavy soils the maximum emergence occurs on undisturbed areas whereas in light soils a shallow cultivation increases emergence substantially.
Burying seed to 50 mm or more virtually eliminated emergence, providing later workings don't bring it to the surface. A single mouldboard ploughing reduces the seed bank by 98%.
Harrowing at crop emergence can be a useful control technique in some seasons.
Burning
Burning stubbles reduces the seed bank by 0-97%. It is best carried out on ungrazed stubbles soon after harvest before the seed has shed. Hot fires back burning into the wind give the best results.
Seed Catching at Harvest.
This reduced Annual Ryegrass seed banks by 50-60% in SA experiments. It is more effective if combined with swathing. (Mathews, 1996).

Origin and History:

Mediterranean.
It was deliberately planted as a pasture plant or under sown in crops in most southern agricultural areas from the early 1900's and is still being planted now.

Distribution:

ACT, NSW, QLD, SA, VIC, WA.

Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

Temperate.
It prefers hot dry summers and mild wet winters.
It is a common pasture plant in regions with rainfall greater than 300 mm.

Soil:

Prefers heavy soils. Common on sandy, loamy red and heavy grey clays.

Significance:

Beneficial:

Important sown pasture grass for both irrigation and dry land areas.
It early season production makes it a valuable component of pastures in winter rainfall areas.
Palatable fodder and high quality hay.
Does not host Root Lesion Nematodes (Pratylenchus neglectus or thornei) (64).

Detrimental:

A major weed of winter crops causing yield reductions. It can start competing with cereals for nitrogen by the 2 leaf stage of the crop. Late sown crops are affected more by competition than early sown crops, but in practise these crops generally have much lower levels of infestation.
Several waves of germination (often stimulated by cultivation) make it difficult to control.
In Victoria, it is estimated to cause losses in crops of $37.4M or 8% of the value of the grain produced (Code, 1990). In WA it is estimated to cause losses in crops of $117M. In 1989, $33M was spent on Annual Ryegrass herbicides.
Weed of rotation crops, perennial crops, fallows, gardens, lawns and disturbed areas.
It can carry root disease (Take-all) of cereals but is probably not a major host.
It results in dockage of grain due to contamination by the seed and contamination by the ergot fungus that grows on the seed.
Can cause hay fever and allergies in humans during spring when it releases massive amounts of pollen.

Toxicity:

Annual Ryegrass Toxicity (ARGT) occurs when seed is infected by a bacterium and nematode combination that causes poisoning. The bacteria (Rathayibacter toxicus) infects the seed of annual ryegrass and produces corynetoxins. It affects sheep and cattle and occurs from October to April usually with most deaths from mid October to mid December. Outbreaks are more common after rain. Mortality rates are often very high. In 1989, 900 farms were affected in WA. 187,000 sheep and 500 cattle had died from ARGT over the previous 20 years. 1991 and 2000 were bad years with 88,000 sheep deaths. In SA, 8000 deaths were recorded in the period from 1955 to 1982.
Annual Ryegrass is also infected by the Ergot fungus (Claviceps purpurea) which is toxic to stock and humans. It is mainly confined to the higher rainfall and coastal areas. The main economic loss is from downgrading of wheat and barley grain due to ergot contamination.
Pollen in spring causes asthma and hay fever in people.

Symptoms:

Staggering or swaying gait, collapse, convulsions followed by death within a few days.

Treatment:

Remove stock from infected areas. Valium has been used to save valuable stock.

Legislation:

None.

Management and Control:

Use and insist on clean fodder, crop and pasture seed to reduce the risk of introducing herbicide resistant annual ryegrass to your paddock.
Graze paddocks heavily in autumn to reduce annual ryegrass plant numbers in the pasture and graze heavily in spring to reduce seed set.
Seed set control. At the flowering stage of Annual Ryegrass, glyphosate CT at 400-600 mL/ha provided 45-90% reduction in seed viability whilst paraquat at 1000 mL/ha was more variable with 20-90% control. At the milk dough stage glyphosate provided 14-76% control and paraquat 64-97% control of seed viability (Mayfield, 1998).
Burn stubbles in summer. Best control on ungrazed stubble with a hot fire burning into the wind.
Tickle cultivate in autumn to encourage germination.
Use Spray.Seed or glyphosate before planting crops. Add carfentrazone if the annual ryegrass has less than 2 leaves. Consider using the double knock technique.
Delay planting in heavily infested paddocks to allow maximum germination and kill with knockdown herbicides.
Apply pre-emergent herbicides and rotate between groups over the crop rotation.
Band fertiliser below crop seed. (Heavy surface applications of fertiliser can also reduce annual ryegrass establishment.)
Increasing the seeding rate of the crop reduces the effect of Annual Ryegrass on crop yield and reduces the amount of Annual Ryegrass seed set. Increased seeding rates in combination with herbicides can result in very low levels of weed seed production.
Use narrow row spacings.
Apply selective herbicides as soon as possible after the annual ryegrass has 2 leaves in cereal crops.
Crop top with selective herbicides when large numbers of escapes occur.
Crop top with glyphosate or paraquat in situations when crop maturity is well in front of annual ryegrass maturity.
Use bipyridyl herbicides for crop desiccation.
Swath crop and burn windrows.
Use seed catchers or destructors at harvest.
Green or brown-manure, hay freeze, make silage or cut for hay in situations where there is likely to be a large amount of resistant annual ryegrass seed set. Follow up with grazing or herbicides to control any regrowth.

Thresholds:

Densities of 30 or more plants/square metre are usually worth spraying in cereals and lupins. This figure for is based on the Annual Ryegrass and crop both being in the 2-3 leaf stage at spraying. If the crop has more leaves than the weed then this figure should be increased to 100 and if the crop has less leaves than the weed then this figure should be reduced to 10 or less. Annual Ryegrass, even at high densities, emerging 3-4 weeks after cereals or lupins rarely affects yields. In cereals, the competition is mainly for nitrogen so early spraying is essential to reduce yield losses. Competition for nitrogen in cereals where the annual ryegrass germinates at the same time as crop from the 2 leaf stage onwards. In Lupins, the competition is for water late in the season so early spraying is not so important.
In lupins, 90 annual ryegrass plants that germinated 6 weeks before the lupins caused 70% grain yield loss, when germinating with the lupins caused 47% yield loss and when germinating 6 weeks after the crop caused no yield loss (560).
The cultivar or variety of cereal has little consistent effect the degree of yield loss caused by Annual Ryegrass. Barley is generally but not always affected less by Annual Ryegrass competition.
The optimum rate of diclofop for ryegrass control can be calculated using the model developed by Pannell (1990) and presented under the economics section of HerbiGuide. This takes into account the weed density, yield potential and prices of grain, application, and herbicide.

Eradication strategies:

Agricultural land.
Bury seed more than 10 cm deep by mould board ploughing with skimmers.
Prevent seed set for 2-4 years.
On light soils tickle cultivate. This is less effective on heavy soils.
Strategies that target the control of seed set can reduce populations fairly quickly. Increase cereal densities to more than 75 plants/m2 (150-200 wheat plants/m2 is suggested).
Cutting crops for silage before Annual Ryegrass sets seed can virtually eliminate it. Green manuring should be equally effective.
Aim to;
1) increase germination and emergence with shallow early cultivations. Bury seed with late deep inversion ploughing. Apply some nitrogen before planting to stimulate germination and make them more susceptible to herbicides.
2) decrease survivorship with herbicides, increased crop density and use good crop agronomy. Delay seeding to allow greater emergence and subsequent control by cultivation or knockdown herbicides before planting.
3) reduce fecundity. Use herbicides and good crop agronomy. Don't use wide row spacings. Plant crop seed as shallow as possible. Band fertilisers. Consider rotations that include silage (or early hay), pasture, sorghum, winter fallows and green manures
4) reduce seed rain by seed catching, seed destructors and harvesting early.
5) reduce seed carryover by burning stubbles as soon as possible after harvest.
Bushland.
Prevent seed set for 2-4 years by herbicides or cultivation. Hand weeding and mowing are usually less effective and grazing is ineffective.
Hand spray until just wet with 5 mL Select® or 10 mL quizalofop(100g/L) or 4 mL Verdict®520 or 30 mL Fusilade®Forte plus 100 mL spray oil in 10 L water in winter when the grass has 2-8 leaves. For larger plants, up to flowering, increase the rates above 3 to 4 fold. These treatments are very selective and do not damage broad-leaved native plants. For larger areas apply 300 mL/ha Select® or 500 mL/ha quizalofop(100g/L) or 100 mL/ha Verdict®520 or 1.6 L/ha Fusilade®Forte with 1% spray oil.
In agricultural areas, Annual Ryegrass populations may be resistant to the grass selective herbicides and glyphosate may be needed.
In winter or spring, spray with 10 mL glyphosate(450g/L) in 10 L water when the Annual Ryegrass is vegetative to the time when the seed heads are just emerging. Most established natives will tolerate this treatment.

Herbicide resistance:

Strains resistant to grass selective herbicides (group A fops and dims), sulfonylurea herbicides (group B), triazine herbicides (group C) and glyphosate (group M) have developed.

Related plants:

Annual Ryegrass (Lolium rigidum) has a glume about as long as the spikelet with 3-9 flowers in each spikelet.
Darnel (Lolium temulentum)
Italian Ryegrass (Lolium multiflorum) has it leaves rolled in the bud rather than folded and has an awn on the lemma.
Perennial Ryegrass (Lolium perenne) has a glume about half the length of the spikelet with 4-14 flowers in each spikelet.
Stiff Ryegrass (Lolium loliaceum)

Plants of similar appearance:

Barley Grass, Brome Grass, Fountain grass, Guildford grass, Lesser Canary Grass, Paradoxa Grass, Quaking Grass, Sand Fescue, Silver Grass, Volunteer Cereals, Wild oats, Toad rush, Winter grass.
Lesser canary grass and paradoxa grass both have reddish pigmentation at the base of the sheath but don't have a shiny underside on the leaf blade. The sap of these species is usually reddish rather than clear as in the ryegrasses.

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P48. Photo.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P150.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P26-27. Diagram.

Ciba Geigy (1981) Grass Weeds 2. CIBA GEIGY Ltd, Basle, Switzerland. P104. Diagrams.

Code, G.R. (1990). Cost of selective ryegrass control and losses due to competition in Victorian winter field crops. Proceedings of the Annual Ryegrass workshop, Adelaide, p137-143.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P114. Photo.

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P328-330.

Gilbey, D. (1989). Identification of weeds in cereal and legume crops. Bulletin 4107. (Western Australian Department of Agriculture , Perth). P6-7. Photos.

Gill, G. S. (1996) Why annual ryegrass is a problem in Australian agriculture. Plant Protection Quarterly 11:193-195

Gill, G. S. (1996) Ecology of annual ryegrass. Plant Protection Quarterly 11:195-197.

Gramshaw, D. (1972). Germination of annual ryegrass seeds (Lolium rigidum Gaud.) as influenced by temperature, light, storage environment and age. Australian Journal of Agricultural Research 23:779-787.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P58. Photo.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #757.4.

Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P968.

Mathews, J.M. (1996). Cultural management of annual ryegrass. Plant Protection Quarterly 11: 198-199.

McGowan, A.A. (1970). Comparative germination patterns of annual grasses in north-eastern Victoria. Australian Journal of Experimental Agriculture and Animal Husbandry 10:401-404.

Monaghan, N.M. (1980). The biology and control of Lolium rigidum as a weed of wheat. Weed Research 20:117-121.

Paterson, J.G. (1977). Grasses in South Western Australia. (Western Australian Department of Agriculture Bulletin 4007). P60. Diagram.

Rerkasem, K., Stern, W.R. and Goodchild, N.A.(1980). Associated growth of wheat and annual ryegrass. I. effect of varying total density and proportion in mixtures of wheat and annual ryegrass. Australian Journal of Agricultural Research 31:649-658.

Wilding, J.L. et al. (1987). Crop weeds. (Inkata Press, Melbourne). P29. Diagram. Photos.

Acknowledgments:

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