Lolium multiflorum (Italian ryegrass)

L. multiflorum is a highly competitive and rapidly growing plant, capable of producing large quantities of seed. It is genetically diverse and displays a high degree of phenotypic plasticity and these characteristics mean that is highly adaptable. It can invade natural grassland and other plant communities that are subject to frequent disturbance.

The taxonomy and nomenclature of Lolium multiflorum is complicated by the many known variants and forms; var. macrostachyum, var. microstachyum, forma longiaristatum, forma cristatum and forma viviparum were named and briefly described by Beddows (1973). L. multiflorum hybridizes freely with L. perenne (L. x hybridum), L. rigidum (L. x hubbardii), L. temulentum and L. remotum. The variability of this species, and its tendency to form tetraploids has resulted in the development of a number of tetraploid cultivars which are commercially available as high-yielding pasture grasses.

An annual to biennial poaceous species. Leaf blades green to dark green, hairless, flat, upper surface evenly ribbed, lower surface smooth and shiny. Length up to 40 cm, width 5-12 mm. Young leaves are rolled in the bud. Auricles are small and narrow. Ligule is white, translucent, shorter than wide. Inflorescence is a spike up to 30 cm in length. The spikelets edge-on to the rachis. Rachis is recessed opposite each spikelet, which more or less fits into the recess. Spikelets consist of 10-20 florets, laterally flattened, green, 15-25 mm long. Only the ternimal spikelet has two more or less equal glumes. Otherwise, only one glume subtending each spikelet, lanceolate, about 10 mm long, less than half as long as the spikelet, outer surface fine-nerved, ribbed like the upper surface of the leaf blade. Lemma lanceolate, 5-8 mm long, five nerved. Awn nearly terminal, fine, straight, about 10 mm long. Palea similar to lemma in shape and size, two nerves with tiny hairs along them. Anthers three; yellow or purple.

L. multiflorum is native to central and southern Europe, north-west Africa and south-west Asia (Hubbard, 1968). It has now spread, largely as a result of its cultivation as a pasture grass, to temperate regions of all continents. It is normally restricted to lowland habitats, but may grow at higher altitudes where drainage and nutrient status permit (Beddows, 1973), although it has not been recorded above 900 m.

L. multiflorum has been deliberately introduced into the temperate regions of North and South America, South Africa, Australia and New Zealand (Lamp et al., 1990) where it is valued as a highly productive and nutritious pasture species. In these areas it has rapidly and successfully spread to become a weed of annual crops, vineyards and orchards. It has also invaded natural grassland communities and is frequently found on waste and regularly disturbed ground.

L. multiflorum is principally a weed of winter- and spring-sown cereals, and is also common in oilseed rape (Brassica napus var. napus), flax (Linum usitatissimum), vegetable crops and orchards. However, it has the potential to be a weed of any crop grown within its geographical range.

L. multiflorum may be easily confused with other members of the genus. Glume usually as long as the spikelet. Species are most easily distinguished on the basis of floral structure. Lolium temulentum has lemmas which are ovate to elliptic and less than three times as long as wide, the caryopsis is also less than three times as long as wide. In other Lolium spp. these structures are more than three times as long as wide.Lolium perenne is a perennial species which has tillers at flowering and fruiting time and lemmas which are usually unawned.Lolium rigidum is an annual species, very similar to L. multiflorum, without tillers at flowering, with (usually) unawned lemmas (awned in L. multiflorum) and spikelets with usually less than 11 florets (L. multiflorum usually has more than 11 florets).

L. multiflorum is able to invade a number of habitats, particularly where ground cover is discontinuous or where there is regular disturbance. It is grown as a forage species throughout its range and frequently occurs as a weed of arable land, or as an invasive species on waste ground, farm tracks and around farm buildings. It has also been reported as an invasive species on natural species-rich grassland and as a riparian weed species. It performs best in areas with relatively high rainfall and on fertile soils. Severe frost, drought, excessive moisture or infertile soils do not favour the establishment and development of L. multiflorum, and growth is best on soils ranging from pH 6 to 7, with 8 as maximum.

GeneticsThe normal diploid chromosome number of L. multiflorum is 2n = 14 (Beddows, 1973). However, its tendency to form tetraploids has resulted in the development of a number of high-yielding commercial tetraploid varieties. Multiple introductions and the outcrossing breeding system of L. multiflorum mean that weedy populations can be highly genetically variable. L. multiflorum readily forms intrageneric hybrids with L. perenne, L. rigidum, L. temulentum and L. remotum. Bennett et al. (2002) used electrophoretic analysis of four enzyme systems to distinguish between Lolium species and suggested that plant breeding and agricultural practices were increasing hybridization between the species. Taxonomic evaluation of Italian populations of L. multiflorum (Dinelli et al., 2002) found a significant number (40-60%) of hybrid individuals in all populations. These were the result of intrageneric hybridization and of intergeneric hybridization with Festuca species. Lolium spp. are able to form hybrids with Festuca arundinacea and F. pratensis (Zeller, 1999; Morgan et al., 2001; Zare et al., 2002) and the potential for formation of these Festulolium hybrids is being used to combine valuable traits in commercial cultivars.Life-Cycle and Growth CharacteristicsThe existence of a range of commercially produced cultivars of L. multiflorum makes generalizations about the species life-cycle and ecology difficult. It may complete its life-cycle as a summer annual, winter annual or biennial, and cultivars which persist for longer than two seasons have been developed. L. multiflorum cv. westerwolds is a strictly annual type.L. multiflorum reproduces solely by seed. In arable soils in Italy, the peak emergence period was autumn (Covarelli and Peccetti, 1989). L. multiflorum grows vigorously in the seedling stage and exhibits good winter growth which continues into spring with some growth in the summer if sufficient moisture is available. It is a prolific seed producer and freshly disseminated seed exhibits little dormancy and high rates of germination. After 4 years burial in soil, initial germination of 93% had fallen to 3% (Lewis, 1958). L. multiflorum is susceptible to freezing temperatures which cause rupturing of the cell walls (Beddows, 1973). The plants require an ample supply of water and are adversely affected by drought.AssociationsMany cultivars and populations of L. multiflorum have been shown to be associated in a symbiotic relationship with clavicipitaceous fungal endophytes from the genus Neotyphodium (Latch et al., 1987; Latch et al., 1988; Nelson and Read, 1990; Wilson et al., 1991). These endophytes modify the physiology, ecology and reproductive biology of infected plants (Clay, 1990). Germination rate and vegetative and reproductive biomass are all increased by this association (Latch et al., 1985; Clay, 1987; Reed, 1987).L. multiflorum is host to a large number of pathogens which may also infect crop plants. Of particular note are Pythium arrhenomanes, which causes root rot disease of sugarcane (Dissanayake et al., 1997); Xylella fastidiosa, which causes leaf scald disease in plum trees (Leite et al., 1997); Xanthomonas campestris (Alizadeh et al., 1997); Polymyxa graminis (Adams and Jacquier, 1994); Barley yellow dwarf virus (Henry and Dedryver, 1991); Burkholderia glumae and B. plantarii, two important pathogens of rice (Miyagawa et al., 1988) and Rice gall dwarf virus (Morinaka, 1986).

L. multiflorum is a food plant for a vast range of herbivores. The most widely reported and economically important of these are listed separately. During a survey, conducted between 1985 and 1989 in Jiangxi, China, 196 species were recorded feeding on L. multiflorum (Long et al., 1990). A large number of other pathogens and pests have been listed for L. multiflorum. These are listed below, but it should be noted that they have little potential for the biological control of weedy populations due to the widespread use of this species as a forage grass.

L. multiflorum is a vigorously competitive species and, as such, many attempts have been made to establish its yield-reducing potential in wheat. In field trials in the UK, densities of up to 200 plants/m² decreased wheat yields by between 12 and 15% (Drennan and Alshallash, 1996). Similar trials in North Carolina, USA, showed that over the density range of 0 to 100 plants/m², L. multiflorum reduced wheat grain yields by 4.2% for every 10 plants/m² (Liebl and Worsham, 1987). In Oregon, USA, wheat grain yield was reduced by 4100 kg/ha with an increase in the density of L. multiflorum from 0.7 to 93 plants/m² (Appleby et al., 1976). In Italy, Zanin et al. (1993) estimated that the economic threshold for the control of L. multiflorum with herbicides was between 25 and 35 plants/m². In trials in Chile, L. multiflorum densities of 10 plants/m² reduced wheat yield by between 1.3 and 1.6%. Every additional 10 plants/m² of L. multiflorum reduced wheat yield by 140-2000 kg/ha (Pedreros, 2001). Competition between a number of wheat varieties and L. multiflorum at a range of densities was assessed in Argentinean field trials. At 150 plants/m², L. multiflorum was more aggressive than wheat; however, differences in the competitive abilities of different wheat cultivars were significant up to 100 L. multiflorum plants/m² (Acciaresi et al., 2001).

L. multiflorum is known to be invasive in its natural and introduced ranges and can reduce the species richness and diversity of natural grasslands when these are regularly disturbed by grazing or cutting.

L. multiflorum is grown world-wide as a highly productive and nutritious pasture grass. It may also be grown as a soil stabilizer to prevent or reduce soil erosion and as a species for revegetating burnt, degraded or contaminated landscapes.

Cultural Control

Control of established plants by mechanical or hand weeding will only be effective if complete removal from the soil is achieved, preventing subsequent regrowth. This is generally impractical, although cultivation is able to successfully control small and recently emerged seedlings. In competition experiments between wheat and L. multiflorum, the yield of wheat was increased at higher N fertilizer rates, and when crop density was increased (Angonin and Caussanel, 1992). Cross-sowing of wheat is not an effective means of controlling L. multiflorum (Appleby and Brewster, 1992).

Chemical Control

In trials in Argentina, pre-emergence applications of trifluralin gave effective control of L. multiflorum, and resulted in increased yield of barley (Scursoni and Satorre, 1997). Clodinafop is recommended for the control of Italian ryegrass up to the three tiller stage (Strachan, 1995) and, in trials in Chile, gave good control of a range of annual grass weeds including L. multiflorum only when sprayed at an early growth stage (Ormeno and Diaz, 1995). Oxyfluorfen applied to broccoli crops in autumn gave 69-97% control in the USA (Eaton et al., 1990). Post-emergence application of metribuzin at the two leaf stage gave good control of L. multiflorum in wheat in Mississippi, USA (Shaw and Wesley, 1991). In South Africa, 80% control was achieved using triasulfuron in wheat and barley (van Biljon et al., 1988). Propyzamide (Purea and Sutton, 1989), fluazifop (Bonanno and Monaco, 1986), chlorsulfuron applied pre-emergence in wheat (Griffin, 1986) and haloxyfop-ethoxyethyl (Visbecq and Morel, 1983) have all been used successfully to control L. multiflorum. Mamarot and Rodriguez (1997) give recommendations for herbicide use against Lolium spp. in a range of crops, for example, EPTC and atrazine in maize; carbetamide in legumes, rape and sunflower; monolinuron in potato; and a wide range of herbicides related to sethoxydim and fluazifop in broad-leaved crops. In Australia, glyphosate and/or paraquat-based herbicides are used for control of Lolium spp. prior to crop sowing (Neve et al., 2003).

Compounds and extracts from a number of plants have been shown to have allelopathic effects against L. multiflorum, though there are no reports of these being used on a commercial scale. Dry foliage extracts from leaves of Rhazya stricta collected in Saudi Arabia inhibited the germination and growth of L. multiflorum (Al-Mutlaq, 2001). Extracts from medium-grain fatty rice bran resulted in 30-96% stand reduction of L. multiflorum (Kuk et al., 2001). The n-hexane-, acetone- and water-soluble fractions from an aqueous acetone extract of lemon balm (Melissa officinalis) inhibited the germination and growth of L. multiflorum shoots and roots (Kato-Noguchi, 2001). Germination and shoot and root growth may also be inihibited by extracts from Evolvulus alsinoides (Kato-Noguchi, 2000). Seed germination of L. multiflorum has been shown to be reduced by aqueous extracts of Tribulus terrestris (Verdú et al., 1999).

Herbicide Resistance

Biotypes of L. multiflorum with evolved resistance to herbicides have been reported in Brazil, Chile, France, Italy, the UK and USA (Heap, 2003). In the UK, seeds were collected from fields in which diclofop-methyl had failed to control the grass. Glasshouse trials were performed on these accessions to determine their susceptibility to various herbicide treatments. Resistance to diclofop-methyl, fenoxaprop and fluazifop was detected, with some evidence of resistance to traloxydim and partial resistance to isoproturon (Moss et al., 1993). Diclofop resistance has also been reported in biotypes from wheat fields in Oregon, USA (Stanger and Appleby, 1989; Gronwald et al., 1992). These biotypes were susceptible to pre-emergence tri-allate + diuron or post-emergent applications of metribuzin and these have been recommended as alternatives for the control of L. multiflorum. Sulfometuron-resistant biotypes have been reported in Mississippi, USA (Taylor and Coats, 1996).

Detailed studies of four resistant L. multiflorum populations in the UK identified resistance to diclofop-methyl, fluazifop-P-butyl, tralkoxydim and partial resistance to isoproturon (Cocker et al., 2001). In three of the populations, resistance was conferred by an enhanced rate of herbicide metabolism. A fourth population possessed an insensitive ACCase target site. An L. multiflorum biotype resistant to diclofop-methyl was investigated in France. It showed intermediate resistance to tralkoxydim and a small increase in tolerance to haloxyfop-methyl, quizalofop-ethyl, sethoxydim and cycloxydim (Prado et al., 2000). Such patterns of cross-resistance are not uncommon in L. multiflorum and other grass weeds.

Of greater concern is the recent confirmation of evolved resistance to glyphosate in an L. multiflorum biotype from a Chilean orchard (Perez and Kogan, 2003).

Biological Control

The potential for biological control of L. multiflorum as a weed has not been investigated due to the economic importance of this species as a forage grass.