Lolium rigidum: botanical characteristics, uses, control and crop management

Introduction

lolium rigidum, commonly known as vallico or rigid ryegrass, is an annual grass of great importance in regions with a Mediterranean climate. It stands out both for its potential forage use, as well as its role as a weed in cereal crops. Its resistance, ecological flexibility, and adaptability to diverse soil types and climatic conditions have made it a species of special interest to farmers, ranchers, and agricultural technicians.

Deep knowledge of the morphological, biological and agronomic characteristics de lolium rigidum It is essential to optimize its use in pastures and meadows, as well as to design effective control strategies in situations where it acts as a herbicide-resistant weed.

Geographic distribution and habitat

lolium rigidum It is native to the Mediterranean basin, from where it has spread throughout southern Europe, North Africa, Central Asia, and the Indian subcontinent. It is commonly found in cultivated fields and annual meadows, as well as on roadsides, field edges, and other environments altered by human activity. Its adaptability has allowed it to successfully colonize regions of Australia and other areas with semi-arid Mediterranean climates, where it currently forms a vital part of mixed-grazing grasslands with species such as subterranean clover.

In the agricultural sector of the Iberian Peninsula, lolium rigidum It is common mainly in dryland areas, although its use as a pasture (crop intended for grazing or mowing) is not so widespread due to its invasive behavior in cereal crops.

Taxonomy and morphological description

• Family: Poaceae (Gramineae)
• Gender: lolium
• Species: lolium rigidum Gaudi

Morphology:

• Annual plant of 10 to 60 cm tall, although under optimal conditions it can reach slightly larger dimensions.
• The stems They can be prostrate or ascending and have roughness on the upper part.
• Its leaves They have a short, membranous ligule with well-developed auricles. The prefoliation is involuted, and the leaf blades are flat, generally smooth and shiny on the underside and slightly rough on the upper surface.
• El root system It is adventitious and fasciculate, facilitating the absorption of surface moisture.
• La inflorescence It is an erect spike, with a rigid rachis, formed by alternate, sessile and laterally inserted spikelets, with a single glume per spikelet that contains 2-11 flowers.
• The anthers They measure between 3 and 4,5 mm, a key characteristic to differentiate the species from other ryegrasses.

It is distinguished from Perennial ryegrass (English ryegrass, perennial) because it is annual and has larger anthers (L. perenne has anthers smaller than 3 mm), and Annual ryegrass (Italian ryegrass) because it has longer spikelets and glumes that can match their length.

Biological characteristics and life cycle

lolium rigidum It is an annual therophyte plant, whose biological cycle begins with germination after the first autumn rains and ends with seed dispersal in spring or early summer.

• Germination: Seeds require light to activate the process, which explains the presence of viable seed banks in agricultural soils that can remain dormant until optimal conditions (temperature, humidity, and sunlight) are found.
• Development: It has a great tillering capacity, generating multiple shoots from the base of the plant.
• Flowering and fruiting: Flowering begins in the spring months and culminates in the production of a vast quantity of seeds (up to 1.500 per plant under favorable conditions).
• Dispersion: Seeds are distributed mainly by the action of wind, agricultural machinery, irrigation water and animals.

Note on persistence and seed bank: 20-35% of the seeds of lolium rigidum They remain viable one year after burial, which contributes to their persistence as a weed in agricultural systems and requires prolonged management for their control.

Environmental requirements and adaptation

lolium rigidum is especially adapted to Mediterranean climates, withstanding long periods of summer drought and minimum winter temperatures. It is less demanding in water than other ryegrasses, such as Perennial ryegrass o Annual ryegrass, and can develop in soils of diverse texture and composition, from sandy loam to clay loam, as long as there are no serious problems with waterlogging.

The optimal pH for this species' development is between 5,8 and 6,7, although it tolerates wider ranges. It resists soil compaction, which facilitates its establishment after frequent mechanical tillage, and thrives in both dry and irrigated land, although yields vary depending on the water regime.

Differentiation from other Lolium species

• Lolium perenne: Perennial species, greater persistence in the field, anthers smaller than 3 mm, less oscillating growth and more suitable for long-term pastures.
• Lolium multiflorum: Annual or biennial, shorter glumes (usually not exceeding 2/3 of the spikelet), frequently with awned lemmas, rapid growth and use in intensive forage crops.
• Lolium rigidum: Annual, efficient self-seeding, larger anthers, significant genetic variability and great adaptation to arid environments.

Synonymy and nomenclature

• Arthrochortus loliaceus Lowe
• Cryptorus loliaceus (Bory & Chaub) Link
• Festuca aleppica Hochst. ex Steud.
• Lolium arenarium Rouville
• Lolium crassiculme Rech.f.
• Lolium cylindricum K. Koch
• Lolium durum K. Koch
• Lolium flagellare Spruner ex Boiss.
• Lolium humile Rust
• Lolium husnotii Sennen
• Lolium lepturoides Boiss.
• Lolium loliaceum (Bory & Chaub.) Hand.-Mazz.
• Lolium lowei Menezes
• Lolium macilentum Delastre
• Lolium multiflorum var. muticum DC.
• Lolium multiflorum var. rigidum (Gaudin) Work.
• Lolium parabolicae Sennen
• Lolium perenne subsp. rigidum (Gaudin) Á.Löve & D.Löve
• Lolium perenne var. rigidum (Gaudin) Coss. & Durieu
• Lolium phoenice Rouville
• Lolium strictum C.Presl
• Lolium subulatum Screw.
• Lolium suffultum Sieber ex Huter
• Lolium temulentum var. oliganthum Godr.
• Lolium temulentum var. subulatum (Vis.) Husn.
• Lolium teres H.Lindb.
• Monerma stricta (J.Presl) J.Presl ex Steud.
• Rottboellia loliacea Bory & Chaub.

Relevance and uses of agricultural and livestock farming

Forage use: lolium rigidum It provides excellent quality pastures in mixed livestock production systems, especially in water-limited regions. Its rapid growth, high crude protein content, and good digestibility make it very attractive for direct grazing or mowing. Protein content can range around 25% in young vegetation and drop to 14% when the plant is tilled. Irrigated crops can be harvested several times a year, while dryland crops typically yield between one and three cuts, depending on rainfall.

• Grazing: Temporary and permanent pastures, in monoculture or associated with legumes such as subterranean clover.
• Harvest: It is suitable for the production of green forage, hay or silage.
• Self-seeding: Its ability to spontaneously produce new plants after the annual cycle guarantees forage utilization with low long-term implementation costs.

Importance as a weed: lolium rigidum It is considered one of the main weeds in winter cereal crops (wheat, barley, oats). In dense infestations it can reduce crop yields by up to 50%, especially due to its competition for water, light and nutrients and its adaptation to the cereal agricultural cycle.

Threats and risks: Toxicity, pests and diseases

Toxicity (ARGT): In Australia, the main limitation for livestock use of lolium rigidum It is the syndrome known as Annual RyeGrass Toxicity (ARGT). This poisoning of livestock is caused by the presence of the bacteria Rathayibacter toxicus (previously Clavibacter), which proliferates in the plant through infection by the nematode Fatal anguinaIn Europe and other Mediterranean areas, this risk is lower, although monitoring for the presence of associated pathologies is recommended.

Plagues and diseases: lolium rigidum is susceptible to fungal diseases such as rust (Puccinia spp.) and powdery mildew (Blumeria graminis). Both can reduce biomass production and forage quality. Among the pests, the action of the green aphid stands out (Schizaphis graminum) and the grass bug (Collaria spp.), which can affect plant biomass and vigor.

Crop implementation and management

• Planting time: At the beginning of autumn to ensure maximum use of the fall rains; in irrigated regions, sowing can be done earlier in late summer.
• Sowing rate: It ranges between 15 and 30 kg/ha, adjusting according to the purpose (pasture, mowing or weed control), the quality of the seed and the sowing technique.
• Depth: Around 1-2 cm to promote emergence.
• Mixes: It can be planted as a pure crop or integrated into meadow mixtures with legumes (especially clovers), which provides nutritional benefits to the forage and improves its nitrogen fixation capacity.
• Irrigation: In irrigated land, frequent and moderate watering during planting promotes rapid initial development.
• Fertilization: It responds very well to nitrogen inputs, which should be distributed throughout the cycle; it may also require potassium and phosphorus inputs depending on the soil's analytical balance.

In dry land, production depends largely on rainfall patterns. Under optimal conditions and with proper management, productions of up to 9 tons of dry matter per hectare per year.

Ways of use and management

• Direct grazing: This is the most common method. Rotational management allows for maximum utilization of regrowth and self-seeding capacity.
• Mowing and haying: Forage can be cut before heading to take advantage of the higher protein content and digestibility.
• Deferred use: It consists of leaving part of the pasture ungrazed and unmown until the seed has matured and fallen, thus ensuring the natural renewal of the pasture for the following season.
• Re-tapering capacity: After the first cut or grazing, the plant can produce new spikes if humidity conditions allow, which extends the harvest window.

The persistence of the crop over time depends on the management strategy. Although lolium rigidum It is annual, in adequate self-seeding systems it has been observed that it can persist spontaneously for several years, although plant density and productivity tend to decrease from the third year onwards.

Local varieties and selections

Commercial varieties and selected native populations can be found on the market:

• 'Wimmera': Australian variety widely used in annual grass mixtures.
• 'Nurra': Variety adapted to Mediterranean conditions.
• Local populations, such as those in the Ebro Valley, have demonstrated productive and forage results comparable to commercial cultivars.

Selecting the appropriate variety or population is a key aspect for optimizing forage yield and minimizing the risks of escape and invasiveness.

Management and control in cereals: herbicide resistance

lolium rigidum It poses serious problems as a weed in winter cereal crops. Its biological cycle coincides with that of cereals, it competes effectively for resources, and has also developed multiple herbicide resistance, which makes conventional handling difficult.

Factors that favor its resistance:

• High infestation density and high seed production.
• Great genetic diversity, which increases the frequency of resistant individuals in the population.
• Germination periods synchronized with cereal sowing, making early eradication difficult.
• Emergence predominates in the surface layers of the soil, so minimal tillage systems can favor its establishment.

The resistances detected include herbicides from the following groups:

• Group A: Acetyl coenzyme carboxylase inhibitors (ACCs), such as diclofop, tralkoxidim, clodinafop.
• Group B: Acetolactate synthase (ALS) inhibitors, such as chlorsulfuron, iodosulfuron.
• Group C2: Inhibitors of photosynthesis in Photosystem II, for example isoproturon, chlortoluron.
• Others: Pre-seeding herbicides such as paraquat, glufosinate and glyphosate, post-emergence and pre-emergence such as prosulfocarb.

Integrated approach to control lolium rigidum in cereal:

1. Prevention:
   • Crop rotation, especially with legumes and sunflowers.
   • Alternation of herbicides with different modes of action.
   • Use of full, unfractionated doses of the herbicide.
   • Mechanical tillage and delayed planting to reduce the viable seed bank.
2. Early identification of resistance:
   • Periodic evaluation of the effectiveness of herbicide treatments.
   • Sending samples to specialized laboratories to confirm resistance.
3. Specific intervention:
   • Alternating application times and mechanisms of action.
   • Planting alternative crops, using direct seeding, stubble management, and specific cultural techniques.

Management requires a medium- to long-term vision, focused on both reducing herbicide use and preserving their effectiveness through sustainable agronomic practices and integrated management technologies.

Environmental contributions and ornamental potential

Although lolium rigidum It has a negative image due to its invasive nature, but under certain conditions it provides ecological benefits:

• It protects the soil from erosion by forming dense vegetation cover in autumn and winter.
• Improves nutrient recycling and soil structure in rotation and green fallow systems.
• It is part of spontaneous vegetation covers that can be used in organic farming programs under controlled management.
• In some low-maintenance gardens or rural ornamental mixes, its vigor and hardiness can be appreciated in temporary natural meadows.

Botanical aspects and etymology

• Lolium: Generic name that, according to classical literature, was already used by Virgil to designate undesirable weeds.
• rigidum: Latin epithet meaning "rigid", alluding to the rigidity of the spike and the general appearance of the plant.

Knowledge of synonymy and nomenclatural history is important to avoid confusing the species with other similar ones, since the genus lolium It is taxonomically complex and exhibits natural hybridizations.

References and bibliography consulted

• Aizpuru et al.
• Bolòs et al.
• Canals & Villanueva
• Canals et al.
• Thin
• Recasens & Conesa
• USDA-NRCS

In addition to the cited works, scientific literature and technical bulletins on herbicide resistance, integrated management, and genetic improvements have been consulted to develop this comprehensive and up-to-date content.

The information presented here about lolium rigidum allows for an in-depth understanding of its biology, management, and agricultural, forage, and environmental relevance. The key to harnessing its potential and minimizing its risks lies in correct identification, the application of sustainable agricultural practices, and the integration of management techniques that reduce its negative impact when it acts as a resistant weed. Detailed knowledge of its biological cycle, its demands, and its genetic diversity make it possible to lolium rigidum a key species in the management of Mediterranean agricultural and livestock systems.