Hordeum murinum ssp. leporinum
Authors: Sheila A. Dean, Global Invasive Species Team, The Nature Conservancy
Scientific Name: Hordeum murinum ssp. leporinum
Common Name: leporinum barley
Hordeum leporinum is a many branched, spreading, or nearly prostrate annual, 15 to 60 cm high.
The seed, carried in florets, breaks from the head in groups of three. This dispersal unit consists of a central, fertile floret and two lateral, sterile florets. The glumes of the central spikelet and the inner glumes of the lateral spikelets are more or less broadened and flattened with hairs along their margin. (These ciliated glumes characterize this species and H. stebbinsii.) The floret of the central spikelet is on a pedicel usually as long as the pedicels of the lateral spikelets, but the awns of the central spikelet itself are shorter than the lateral awns. (This shorter central spikelet distinguishes H. leporinum from H. murinum.) The awn is 1.5 to 2.5 cm long, stiffly erect and spreading. Within the spikelet, the anthers are 0.8 to 1.5 mm long with a strongly bilobed base. (Cocks et al. (1976) state that H. leporinum can be best distinguished from H. stebbinsii by the larger size of the anthers in the central floret, by the exertion of the anthers at flowering, and by a looser spike).
Hordeum leporinum is an introduced, annual grass. In Mediterranean climates, it can be a successful invader where land has been disturbed by grazing or construction. With continued land disturbance in particular climatic conditions (wet winters and dry summers), barley grass can persist and become dominant. The grass is of high forage value early in its growing season, but the seed awn has proven harmful to stock. Control may be possible through mowing, and possibly through application of herbicides, but little research on control has been conducted in the southwestern United States, with no known research in Arizona.
The genus Hordeum is thought to have originated in western Asia. Hordeum leporinum is indigenous to the Mediterranean region where it typically occurs in disturbed areas. The species is a valuable forage plant in the southern USSR, Argentina, and in portions of Australia. It is thought to have been introduced to North and South America, and to Australia, by the early nineteenth century (Smith 1972, Cocks et al. 1976). In North America, wild barley can be found from Maine and British Columbia to northern Mexico; it is absent in most midwestern states (Gould 1951).
Almost all published research on Hordeum leporinum has been conducted in Australia, with some limited information from California. Sometimes information is conflicting which may, in some cases, be due to confusion over different forms in the Hordeum murinum complex. (See discussion on ecotypes in Biology- Ecology).
In Arizona, Hordeum leporinum is common on disturbed soil of roadsides, irrigation ditches, vacant lots and lawns. It is usually considered a weed pest where it is most often found in cultivated crops, including grain and alfalfa (Gould 1951, Parker 1973). Kearney and Peebles (1951) note its Arizona location in Coconino and Cochise counties. However, two sources from southern Arizona do not consider it to be a problem in the State (P. Ogden pers. comm., D. Robinette pers. comm.). In California Hordeum leporinum appears as a common spring weed in cities and towns, along roads, fencerows, ditches, rubbish dumps, disturbed soils, and in and about croplands (Crampton 1974).
Hordeum leporinum is ubiquitous in annual pastures of southern Australia that are characterized by a Mediterranean climate. It can be common in perennial pastures as well. The grass sometimes increases when pastures are grazed, though it often diminishes under extremely heavy grazing. By the 1960's it was usually considered an undesirable weed until it was recognized as high quality forage early in its growing season. As the plant matures, the awns on the seed become noxious and harmful to stock, irritating their eyes and skin, and damaging the wool (Warr 1981). Wild barley often invades cultivated pastures as soil nitrogen increases; it still presents a problem as a weed in Australian alfalfa fields and in pastures sown with clovers and medics (Medicago spp.).
Hordeum leporinum is found from 275 to 2,750 m in Arizona. It is a common understory plant in mesquite bosques of Arizona's Hassayampa River (H. Richter, 1990). In 1951 barley grass was described as the most common barley in California ranges, being especially abundant in valleys and foothills where it frequently formed pure stands (Sampson et al.). It grows most often on well-drained soils and sometimes on clay in grasslands of California's Central Valley and coastal ranges (T. Briggs, 1990). In Australia, it is often found in dry temperate grasslands, semi-arid shrub woodlands and also in eucalyptus shrublands. Barley grass often grows on meadow podsols, preferring medium to heavy-textured soils of high fertility that are mildly acid to alkaline (pH 5.0 to 6.8) (Rossiter 1966, Moore 1970, Davison 1972). Although barley grass has shown an ability to survive temporary drought, it is most common in Australia where rainfall exceeds 475 mm (Cocks et al. 1976). Smith (1972) states that barley grass usually invades alfalfa pastures in areas where annual rainfall ranges from 250 to 500 mm. (These sites of lucerne invasion may include both the stebbinsii and leporinum forms of Hordeum (Cocks et al. 1976)).
When Hordeum leporinum is a common component of southern Australian pastures, it usually invades sites dominated by winter-growing annual species. For instance, it is often associated with another exotic, Wimmera ryegrass (Lolium rigidum) (Smith 1972). Other common species growing with Hordeum in annual pastures are subterranean clover (Trifolium subterraneum) and barrel medic (Medicago truncatula). Wild barley grows as a few scattered plants or else dominates the pasture; barley densities within a pasture may vary from one year to the next. It has been suggested that these variations could be attributed to either soil fertility or to temperatures during germination in early autumn (Smith 1968a).
On highly acid soils, pastures of subterranean clover, Phalaris, or communities of annual medics often become dominated by barley grass. This has been shown experimentally to result from high levels of soil nitrogen (Smith 1968c). Where perennial grasses have been killed by drought or insects, barley grass also often invades and it is commonly found after periods of heavy grazing (Moore 1970).
Hordeum leporinum is a vigorous winter annual. After flowering in the spring, the grass matures rapidly to produce a large number of viable seeds. These seeds easily disperse when the long awn attaches to stock and wildlife, and then to the soil. The majority of seeds remain dormant during the heat of the summer, not germinating until the autumn.
Some researchers ask why Hordeum leporinum is so prolific in the Mediterranean climate of southern Australia; Smith (1972) notes that it is particularly well adapted to both the climate and forms of range management used on the continent. Some more general reasons for its success as an invader species throughout the world include its early germination and early rapid growth rate (relative to associated exotics), as well as its high seed production and efficient dispersal mechanism (Biddiscombe et al. 1954, Smith 1972).
In Arizona, Hordeum leporinum flowers mostly in March and April at lower altitudes, and up to October at higher elevations (Parker 1973). Flowering of barley grass in Australia is completed in one month, usually between mid-August and mid-September (Australia's early spring), with the plant maturing by the third week of October (Biddiscombe et al. 1954).
Hordeum leporinum autumn flowering of plants from seeds germinated by mid-summer rains. However, most flower initiation is partly controlled by moderate winter cold. Unpublished data suggests that it must be cold enough for initiation, but without too much frost which causes death; these conditions are apparently more common in southern Australia than on other continents (Smith 1972). Growth to head emergence and seed maturation are then accelerated by rising spring temperatures, and depend on spring rains or soil moisture storage from winter rains. (Spring rainfall in southern Australia is also more reliable than in California or on Mediterranean lands).
Growth to seed maturation is rapid, and ripe seed production is copious. Halloran and Pennell (1981) found 19 to 29 seeds produced per head. Barley grass has demonstrated a superior capacity to set seed in difficult seasons, such as during droughts. In addition, its dormancy is assured when summer daytime temperatures are high. Germination appears to be prevented by high summer daytime temperatures, while it is induced by lower autumn temperatures (Smith 1968a, 1972). High seedling density, copious seed production, preservation during the adverse dry season and establishment of a dense sward in the favorable season assure the success of barley grass in southern Australia (Smith 1972). This is particularly true in relation to native perennial grasses (Stipa, Chloris, Digitaria spp.) which, in experiments, have demonstrated greater germination needs for moisture than the exotics (Biddiscombe et al. 1954).
The structure of the seed awn facilitates dispersal by stock animals, and by the cutting of hay which is later laid out on the ground. The seedlings establish readily on the surface, being relatively drought resistant (Smith 1972). Most barley grass germination occurs on soil surfaces that tend to set hard (Smith 1968a, McGowan 1969). Seeds sown on the surface give rise to larger shoots than buried seeds. In addition, the seeds are too large for ants to carry away, and the awn often repels ingestion by foraging animals. The seed is thus well protected in the summer before autumn germination (Smith 1968a).
The main germination time in Australia is the autumn-winter period (Smith 1968a). Germination is favored by late summer rains (January). Biddiscombe et al. (1954) found that barley grass germinates primarily from late February to early May when soil temperatures range from 18 to 24° C. A temperature of 30° C is the upper limit for germination.
A laboratory experiment found that germination occurred in 12 days at constant air temperatures set from 8 to 30° C. This demonstrated Hordeum leporinum's wide tolerance to temperatures for germination, especially in relation to the other tested plant, Lolium rigidum (Wimmera ryegrass, also an exotic). Effects of temperature alternation on germination were weak and insignificant. Germination for barley grass ranged from 49% to 59% between the temperatures of 8.4 and 29.3° C; germination percentage (number of seedlings in relation to seeds) did not increase steadily with the temperature. Barley grass germinated much more rapidly within a 48 hour period than Lolium. When seeds were exposed to high temperatures in moist conditions, Hordeum seeds were not killed until after seven or more days at 3° C, again showing a tolerance to high temperatures. (In other studies, seeds have also demonstrated an ability to remain dormant, but viable, in hot and dry conditions). Germination and establishment (percentage of viable seeds sown) were found to be slightly, but not significantly, higher on sand than on loam. Hordeum was able to germinate in much drier soil solutions; at 15 atm, 50% of viable Hordeum seed germinated in ten days. In addition, the Hordeum seeds showed a lower uptake of water than the Lolium seeds, with the per cent water per the dry weight of seed varying from 9 to 31% (Cocks and Donald 1973a).
This experiment demonstrates Hordeum's success in relation to a co-occurring exotic grass. In the Australian climate Hordeum leporinum has the advantage of gaining an earlier, more rapid, and more complete germination in autumn. It can germinate in a wider range of temperature while also needing less moisture. Hordeum also can germinate easily when lying on the soil surface and it shows less of a requirement than Lolium for temperature alternations, the daily high being of most importance (Cocks and Donald 1973a). These results are consistent with McGown's (1970) note that Lolium is often the dominant grass in the first year or two after a period of cropping. With grazing, however, it is soon replaced by Hordeum, Vulpia and Bromus.
A small proportion of seed remains dormant but viable through the first growing season, insuring a seed source for the following year. Some authors stress that almost all seeds germinate during the first autumn after flowering (Smith 1968a, McGowan 1970, Halloran and Pennell 1981). (McGowan found only one seed remaining in a cultivated test quadrat of 406 square cms.). The seeds showing delayed germination were smaller (less than 0.004 g) and were usually found at the upper and lower extremities of the head; delayed germination is probably related to late development and position of the seed, rather than to its size.
Hordeum leporinum's adaptability to Australian conditions appears to result from a number of factors. These include its ability to remain dormant at high summer temperatures, its protective barbed awn, and its germination at the soil surface over a wide range of temperatures. In addition, a rapid germination rate even when moisture levels are low enable barley grass to withstand difficult seasonal changes. Finally, its early maturity in relation to other plants, delayed germination of other seeds, its high levels of seed production, plus the high fertility (92%) of the head, give it an advantage in the Mediterranean climate of southern Australia (Biddiscombe et al. 1954, Smith 1972, Halloran and Pennell 1981, Chapin et al. 1989).
VEGETATIVE DEVELOPMENT AND RESPONSE TO NUTRIENTS:
Hordeum leporinum is capable, in Australia, of high levels of herbage production in the early part of the winter growing season. This productivity decreases with time after germination. Autumn production rates amount to 22-25 kg/ha with winter rates of 10-14 kg/ha; barley grass develops dense swards relative to associated grasses (clover and rye grass)(Smith 1968d, 1972). Root growth in a clay loam soil is fibrous, penetrating vertically about 75 cm with a lateral spread not exceeding 8 to 10 cm. The root mass is concentrated primarily in the top 15 cm of the profile, with a gradual decline between the 15 and 30 cm levels (Biddiscombe et al. 1954).
In an experiment conducted in seed boxes, moisture stress affected the growth of Hordeum leporinum only when germination took place early in autumn (when the seasonal change occurred earlier than usual). Otherwise barley grass survived dry conditions far better than an associated pasture plant, Trifolium subterraneum. This may be a reason for its predominance in irrigated areas that suffer seasonal moisture stress when the irrigation is limited (Smith 1968c). It was also found that the highest production occurred in swards with added nitrogen that germinated early and that suffered no moisture stress. Density influenced yield significantly; higher density swards compensated for late germination. Added soil nitrogen also produced larger barley grass plants.
Seedlings can be damaged by frost, but they are rarely killed and the damage is often reduced by high nitrogen levels in the foliage (Smith 1972). In comparative growth experiments, barley grass was found to be more resistant to frost when nitrogen levels were high; where frosts are common, factors that affect the level of foliage nitrogen may determine the success of barley grass. These factors could include frequency of defoliation (in experiments plants were cut at weekly intervals), leaching, denitrification in water-logged soils, the abundance of a co-occurring legume, increased size before defoliation and the addition of fertilizers. Cold, frosty winters accelerate maturity of barley grass, with the seed heads emerging earlier (Cocks 1974).
When three different densities of Hordeum leporinum were exposed to varying soil nitrogen levels, Hordeum responded most markedly in yield to added nitrogen (urea) when the grass was growing at a high density (Cocks 1974). Though responsive to nitrogen fertilizer additions, nitrogen has no additional benefits when a mulch was applied first (Campbell and Beale 1973). Protein and nitrogen content both decrease with time after flowering (Biddiscombe et al. 1954, Cocks 1974).
Although Hordeum leporinum in Australia prefers fertile soil, it can live at sites low in phosphorus. Chapin et al. (1989) found through experimentation with several Hordeum species that the relative growth rate was not positively correlated with soil fertility levels. They concluded that a low relative growth rate is not an adaptation to low soil phosphorous and that seed size, rather than soil fertility, is the major determinant of early plant size. The authors speculate that species like Hordeum leporinum may have evolved a rapid growth rate in poor soils by taking advantage of relatively short but conducive growing conditions when temperatures and moisture levels are favorable. Other authors have noted that barley grass does nevertheless respond to added soil nutrients. This responsiveness was illustrated by a twelve year field experiment where four levels of phosphate were applied in sown clover pastures. Rossiter (1964) found that during the second five years, barley grass made up most of the annual grass component where phosphate applications had been high. Other species found in high percentages with barley grass were cape-weed (Cryptostemma calendula) and brome grass (Bromus rigidus).
The California Nature Conservancy has found that depths of up to 20 cm of residual dry matter favored the growth of Hordeum leporinum. Barley grass grows well at any level of these natural mulches that accumulate up to that depth (T. Briggs, 1990).
COMPETITIVE RELATIONSHIPS AND POPULATION DYNAMICS:
The early maturation of barley grass enables it to complete its life cycle ahead of later-maturing associated annual and perennial species. Then it is better established and more resistant to difficult environmental conditions than plants germinating later. This feature also offers greater assurance for seed production in seasons and environments of short growing period (Biddiscombe et al. 1954, Smith 1972). Cocks and Donald (1973b) argue that plants which germinate faster than neighboring plants often have an immediate and longer-term competitive advantage, gaining progressively greater advantages for light, water and nutrient resources.
Wimmera ryegrass (Lolium rigidum) is also an exotic annual, but it is sown in Australian pastures for forage. Barley grass often invades these pastures, sometimes becoming dominant. Barley grass germinates much more rapidly than ryegrass, and the former also germinates more easily at the soil surface, even when conditions are dry. The germination rate is more strongly stimulated by short prior periods of wetting and drying without lolium’s germination requirement for diurnal temperature fluctuations. Barley grass also recovers more rapidly from defoliation than ryegrass (Smith 1968b, Cocks and Donald 1973a). Another explanation for replacement by barley grass is that ryegrass seed is more easily removed by ants than the heavier and larger barley grass seeds (McGowan 1969). Also, at high levels of nitrogen and calcium, barley grass was found to be significantly more competitive than Wimmera ryegrass (Moore 1970). Experiments on the early vegetative growth of barley grass and rye grass indicate that when annual pastures re-seed naturally, plants usually grow at high density. Under these conditions Hordeum leporinum can gain an early competitive advantage over ryegrass (especially as the larger leaves of barley grass create shade), and can progressively gain dominance. However, if for some reason barley grass is growing at lower densities, the faster relative growth rate of Lolium can enable it to overtake the barley grass seedlings (Cocks and Donald 1973b).
Even though ryegrass seeds portray a better tolerance to extended high temperatures in moist conditions, this does not seem to be enough of an advantage to assure its success over barley grass (Cocks and Donald 1973a). However, Smith (1968b) found that ryegrass can survive more easily than barley grass when frosts are frequent and soil nitrogen low, or when ryegrass is growing at a high density.
In comparing the growth response of barley grass to ryegrass and another associated pastures species, silver grass (Vulpia myuros), barley grass showed the least response to nitrogen. This relationship was strongest when all plants were growing at high densities (Cocks 1974). In noting the earlier germination of Hordeum as compared to the other two grasses, McGowan (1970) suggests that Lolium's longer dormancy may explain why it is more likely to persist as a weed of winter cereal crops rather than also persisting in pastures, as barley grass does. (Cultivation before the sowing of a cereal crop kills those Hordeum seedlings that have already germinated).
The Mediterranean climate of southern Australia is also favorable to subterranean clover (Trifolium subterranean). This and other legumes (Medicago spp., alfalfa) are commonly sown companions of barley grass. Annual medics, for instance, are used as cereal pasture rotations on crop-livestock farms (Carter 1987). Success of any of these legumes raises the nitrogen soil level, increasing invasion of the grass (Smith 1972). Seedling survivorship of barley grass and the associated plant Erodium, was greater than that of Medicago spp. during periods of low moisture (Biddiscombe et al. 1954, Smith 1968c). Smith (1968c) found in experiments that if cold temperatures began earlier in the autumn season, and if these colder temperatures lasted longer, barley grass dominance was less likely in pastures sown with subterranean clover. However, barley grass showed an advantage over the clover if moisture levels were low, if autumn began late and if sward density was high.
Plant interactions in response to superphosphate additions were tested in a long-term (12 year) field experiment in southwestern Australia. Superphosphate was applied at four levels in sown clover pastures. At the two highest levels of application (125 to 375 kg/ha), barley grass made up most of the annual grass component during the last five years of the study. When grazing had occurred, barley grass far exceeded another prevalent annual grass, Bromus rigidus. When barley grass was dominant, capeweed ('Cryptostemma calendula) and Erpdoi, (native to Australia) also became less common (Rossiter 1964).
In studying winter annuals (Hordeum leporinum, medicago spp., Erodium) and native perennial grasses (Stipa, Chloris, Digitaria spp.) in pastures of New South Wales, Biddiscombe et al. (1954) found three factors that assured a regular recurrence of the annuals as an important winter component of the pasture. First, they were characterized by a free-seeding habit, even when ripening was hastened by hot, dry conditions in early spring. Second, the annuals were capable of germinating within a wide soil temperature range, guaranteeing successful germination at any effective rainfall. Third, their rapid growth rate insured reaching maturity prior to dry summer conditions. High spring production was found to depend on an adequate moisture supply in autumn or late summer. In general, the winter annuals achieved vigorous development in association with a relatively dense stand of summer perennial grasses. The perennials were far more susceptible to variations in available moisture; seasonal temperature variations affected seasonal distribution of annuals to a lesser extent. The composite pasture showed a September maximum in green forage production of the annuals, while the perennials peaked in March.
Kriedemann and Anderson (1988) report that Hordeum leporinum is remarkably competitive with cultivated wheat (Triticum aestivum) even when soils are deficient in trace elements. In laboratory experiments, they found that barley grass displayed an advantage over wheat (especially on Mn/Cu impoverished sites) due to the growth of a larger root mass and to a more efficient uptake mechanism of trace elements. As Mn/Cu levels in solution cultures were lowered, barley grass partitioned relatively more biomass towards roots than the wheat did.
In Australia, when annual grasses were introduced, webworms (Hednota) found barley grass palatable and insect numbers increased, with serious outbreaks occurring every few years (Wallace 1970).
Hordeum leporinum is part of the Hordeum murinum complex and has often been confused with Hordeum murinum and Hordeum stebbinsii (synonym H. glaucum) (Covas 1949, Smith 1972, Cocks et al. 1976). Hordeum leporinum (Link) was named as a new species in 1834, whereas Hordeum murinum was first described by Linnaeus in 1753. Hordeum leporinum has been considered a separate species by some because of its ecological distinctiveness (preferring warmer, drier climates), and a subspecies of Hordeum murinum by others due to morphological similarity. (The two can be differentiated by leporinum's much shorter central spikelet relative to the lateral spikelets). The two are interfertile and no chromosomal differences can be found. It has been suggested that most North American plants classified as murinum are mostly Hordeum loporinum (Rajhathy and Morrison 1962). In GRASSES OF THE SOUTHWESTERN UNITED STATES, Gould (1951) does not describe Hordeum murinum and states that Hordeum leporinum has long been called Hordeum murinum. Another author (Davison 1951) suggests that the two form a continuous morphological cline in Europe, with murinum in the northern and cooler climates and leporinum more restricted to Mediterranean climates; the murinum form is abundant in New Zealand and Tasmania but totally absent in Australia where Hordeum leporinum is common. The two are now most often considered separate species due to their geographical and ecological distinctiveness (Smith 1972).
Cocks et al. (1976) discuss the third member (H. glaucum, synonym H. stebbinsii) of the Hordeum murinum complex and have found that it has also been confused with Hordeum leporinum. These authors suggest that in southern and western Australia the glaucum form grows where rainfall is less than about 425 mm, while the leporinum form grows where rainfall exceeds 425 mm. Differences between the two forms consist of the following: the leporinum form is more vigorous, more hairy and a darker green compared with the less vigorous, almost hairless, bluish green glaucum form. In addition, Hordeum leporinum flowers later than the glaucum form, with the latter flowering an average of 138 days after sowing. Hordeum leporinum flowers anywhere from 122 to 169 days after sowing. Hordeum glaucum may be the most widespread barley grass in Australia. These conclusions were made after cultivating (under controlled conditions) plants that had been collected from 88 sites in two states of southern Australia. Cocks et al. (1976) believe that the following authors working with barley grass (and cited here) were actually working, in part, with Hordeum glaucum. These include Cocks and Donald (1973a), Smith (1968a) and McGowan (1969).
In the United States, Hordeum leporinum is a vigorous species that grows in intermediate habitats between the more zerophytic glaucum form (H. stebbinsii) and the more mesophytic murinum form (Covas 1949). Kearney and Peebles (1951) list Hordeum leporinum and Hordeum stebbinsii, noting that each are sometimes called Hordeum murinum; these authors describe a wider range for Hordeum stebbinsii, including Coconino, Mohave, Yavapai, Maricopa, Cochise and Pima counties.
Hordeum leporinum can be an important component of pastures in southern Australia in late autumn, winter and early spring. Sheep preferentially graze barley grass and it comprises a major part of their winter diet. However, in late spring and summer, especially after flowering, it has an adverse effect on sheep production, causing production losses (in extreme cases causing death) as a result of seedheads penetrating the eyes, mouth, feet, wool and skin (Smith 1972, Warr 1981). Research has been conducted in Australia on the relationship of grazing to both early season growth of barley grass and to later season control. This research is extensive, sometimes conflicting, but is summarized here because it includes additional ecological information on Hordeum leporinum.
Some workers have found that late winter and early spring grazing increases the abundance and percentage of barley grass in pastures (Smith 1968d, 1972, McIvor and Smith 1973). For instance, in pastures containing roughly 80% barley grass in addition to subterranean clover, capeweed (Arctotheca calendula) and Wimmera ryegrass, sheep were allowed to graze until late winter when grass growth was accelerating in response to rising temperatures. At that time three different levels of grazing were tested for two years. Moderately grazed plots were those where pasture was grazed to a length of 2.5 to 5 cm until early spring, then remaining ungrazed until mid-summer. Heavily grazed plots were grazed intensively until the cessation of spring growth. (No animal densities were noted in these descriptions of grazing levels). After one year, seed set was not significantly affected in grazed plots and amounted to more than half a ton of seeds per acre. However, grazing did increase subsequent barley grass germination significantly, especially on the heavily grazed pasture. Moderate grazing resulted in the highest number of viable seeds (855/ sq. lk.), as well as the largest seeds (6.25 mg). After two years of treatments, the area that was heavily grazed was almost completely dominated by barley grass with very little ryegrass or clover remaining. The heavily grazed treatment thus resulted in a significantly higher percentage of barley grass, though with a lower total yield of all plants than in the moderately grazed plots. Heavy grazing reduced both the dry matter production (lb/ac) at seed set as well as the length of stems on which seeds were set, but it increased tillering and heads produced. Moderately grazed plots resulted in the highest total seed production, germination and numbers of viable seeds of barley grass (Smith 1968d).
Capeweed dominant pastures (36% with 27% barley grass and 4% subterranean clover) were also subjected to grazing treatments. (The other annual grasses present included Bromus mollis, silver grass and ryegrass, with additional miscellaneous species. Grazing treatments included no grazing after August 18, close grazing until September 21 ("early grazing") and close grazing until November 4 ("full grazing"). (Again no animal densities are mentioned). Dry matter production was then determined at the end of April, with the result that total dry pasture residue was significantly reduced in the full grazing treatment. The number of viable barley seeds germinated was highest in the early grazing treatment, and lowest in the full grazing treatment. In this one year study, the percentage of barley grass increased with grazing and was highest under full grazing (almost 50%), as was the percentage of capeweed. The study gives no explanation, however, as to why the highest number of viable seeds were found when pastures were not grazed or were grazed early, or why the number of seedlings was highest when the pasture was not grazed (1.8/sq. dm.)(McIvor and Smith 1973).
Robards and Leigh (1967) found that the biomass of Hordeum leporinum increased when grazing took place as plants were approaching maturity in late winter (August and September). These results were found when "crash grazing" was imposed over different combinations of months from May to December. The authors speculate that the higher biomass resulted from an increase in tiller number stimulated by fresh growth from basal buds after flowering shoots were removed by stock animals.
In annual subterranean clover pastures, Hordeum leporinum was the most abundant invading species after four years of grazing treatments. At two different stocking rates (8.1 and 12.3 ewes/ha) invasion was minimal until after a dry spring of the third year. At the higher stocking rate, barley grass dominated over ryegrass and silver grass. The most significant difference between the two stocking rates was only seen only when the pastures were sown with oats and/or alfalfa; in these cases barley grass invasion (percentage in relation to invasion by ryegrass and silver grass) was much greater at the lower stocking rate (Fitzgerald 1976).
Hordeum leporinum has been reported to first increase and then decline with progressively heavier grazing on subclover pastures in Australia (Rossiter 1966). Similar results were found on the Pacific coast range of northern California. Here, both grass-woodland and improved grasslands were subjected over five years to three grazing treatments. The Hordeum leporinum component of grasslands increased under 150% of moderate grazing but declined to its lowest frequency at 200% of moderate stocking. (The means of these stocking rates ranged from 0.6 to 8.0 ewes/ha in woodlands and from 1.8 to 10.0 ewes/ha in grasslands). Wild barley and Bromus Mollis were more sensitive than Festuca spp. to heavy use (Rosiere 1987).
Another test successfully controlled Hordeum leporinum through the use of very heavy grazing rates in southern Australia. Over three years, grazing was deferred to different time periods after the start of irrigation with the result that all barley grass densities were reduced and clover establishment enhanced. Barley grass was almost completely eliminated when grazing was deferred for 20 days after the opening of autumn irrigation with continuous grazing after this at approximately 20 sheep/ha. This grazing level was extremely high and not even typical of livestock management for that area (Myers and Squires 1970). Smith (1972) points out that such a deferment period would be more difficult to achieve in dryland pastures and that such heavy grazing in autumn could damage other components and reduce pasture production.
In a five year experiment also involving high stocking rates, Carter (1987) found that by the third year in medic fields, barley grass was so dominant that associated subterranean clover set no seed. However, at the highest stocking rate (22 sheep/ha), barley grass was present but was sparse; only cluster clover and "winter grass" increased in percentable botanical composition with this treatment. The author suggests that barley grass was rare at this stocking level because its seeds do not survive passage through the digestive tract of sheep.
Hordeum leporinum proportions were also found to decrease with increased grazing in fields that were dominated by Hordeum leporinum, Erodium crinitum, medics and silver grass. Field experiments over four years resulted in a lower contribution by barley grass to the pasture within each year when stocking rates were higher. The least barley grass grew at the highest and unchanging stocking rate of 4.9 sheep per hectare. However, over the four year period of grazing treatments, the average barley grass content of the three grazing levels increased from 19% to 62%. Perhaps the tested grazing levels were still low enough to favor barley grass growth over a period of four years (Campbell and Beale 1973).
RESPONSE TO MANIPULATIONS (IRRIGATION, MOWING, FIRE, CHEMICAL):
The seasonal onset of irrigation appears to be critical in determining barley grass populations. If irrigation begins in late autumn (April to May), the pasture is grass dominant. If it starts in early autumn (February), the pasture tends to be clover dominant. However, barley grass invades irrigated pastures irrespective of the starting date (Myers and Squires 1970).
Some forms of mowing have proven effective in controlling barley grass. Three different mowing treatments were found to significantly reduce seed set and germination in a two year experiment on pastures that initially contained approximately 80% barley grass. (Irrigation, however, caused a significant increase in seed numbers and germination on mowed plots). The greatest reductions occurred when the barley grass was cut close to the ground about ten days after the heads started turning color and the herbage then removed. When subterranean clover was sown, seed setting of barley grass was significantly reduced. When these treatments were performed a second season, the effects were not cumulative. Nevertheless, after the second year, the proportion of barley grass decreased to 17% where it had been cut for hay as compared to approximately 50% where pastures were lightly grazed and not mowed (Smith 1968d). In California, if barley grass is mowed or grazed before the heads appear, areas become less infested (Sampson et al. 1951).
Mowing also reduced the proportion of Hordeum leporinum and hay cutting almost eliminated it from pastures initially containing 27% of Hordeum leporinum. (Hay cutting in this experiment consisted of cutting to 2.5 cm in the spring and removing the herbage; the other mowing treatments included "topping", where plants were cut to 5 cm with herbage left on the plots and "silage" which was identical to hay cutting, but with plants cut one month earlier). As barley grass decreased, capeweed (Arctotheca calendula) and clover increased (McIvor and Smith 1973). Similar results were found in Medicago spp. dominant pastures. When barley grass was cut to ground level 28 days after the first January rains, yields were lower than in other grazing and cutting treatments. This defoliation in the establishment phase severely depressed subsequent growth and germination of barley grass. Germination of barley grass seed was enhanced by a covering of surface mulch, but this benefit declined with successive germinations (Campbell and Beale 1973).
Other attempts at mowing in California only resulted in barley grass returning in full vigor the following season. These treatments were attempted with no additional management, such as burning, grazing or planting with native grasses. It is speculated that replanting with native ryes following mowing could initiate a replacement of barley grasses; planting with native bunch grasses is thought to be less effective (T. Briggs 1990).
Rossiter (1966) notes an effect of fire on annual grasses, with their pasture content decreasing from 77% to 12% during the spring following a summer's severe burn. This effect on composition change was less when preceded by heavy grazing.
Several years of data have been collected in California on the response of grasslands to prescribed burns (T. Briggs 1990). Hordeum leporinum was found to be the annual grass most sensitive to burning. When a grassland contained up to 90% of barley grass, this percentage was reduced to less than 5% after burning. This level was found to remain the same for up to three years with no other management.
Invasion of wild barley on seedling alfalfa in the high desert of southern California prompted application of pronamid (1 lb. ai/acre) and propham (6 lb. ai/acre). These amounts, applied in mid-February, when the barley was 20-25 cm tall, provided control. In another test on grasses already 15 cm tall, DPX-Y6202 and fluazifop provided superior control, with no apparent phytotoxicity in the alfalfa (Cudney and Orloff 1986). When herbicides were applied to the soil just after emergence (Jan. 25), they had little effect. Of pre-emergent herbicides, pronamid offered the best control, with a combination of 2 lbs. ai/acre of pronamid and paraquat the best overall. (Orloff and Cudney 1986). Neither of these brief research reports notes deactivation rates.
Invasion of legumes by barley grass was also controlled with paraquat and 2,2- DPA at Cowra, Australia. Paraquat killed barley grass and other weeds when sprayed at 1 pt./acre on July 20. The 2,2-DPA had a more specific effect on barley grass when sprayed at 3 lb./acre. The alfalfa was retarded by 2,2-DPA for about five weeks, while the retarding effect of paraquat was only seven days (Tickner 1968).
In northeastern Victoria, 2,4-D, 2,2-DPA, paraquat and diquat were tested on pastures composed of phalaris, Wimmera ryegrass, barley grass, silver grass and subterranean clover. Only 2,2-DPA and paraquat affected grass compositions, as measured on October 17. Paraquat applied in May reduced the proportion of barley and silver grass. Barley grass was also reduced by 2,2-DPA applications in either May or July, although ryegrass increased. (Herbicides were applied with 25 gallons of water per acre). All plants were fairly resistant to an April spraying. The higher the proportion of clover in the pasture, the greater its loss from 2,4-D, whereas when the grasses were more abundant in relation to the clover, they were also more affected by paraquat or diquat. Both grasses and clover were severely affected by high rates of 2,2-DPA. Effects on clover did not carry over into the following year (McGowan 1970).
Squires (1963) also found no carryover affect on clover by herbicides from one year to the next. In irrigated subterranean clover, barley grass was treated with three herbicides (also in southern Australia). The clover was found too intolerant of 2,2-DPA to warrant further testing. White clover (Trifolium repens), however, withstood an application of 2 pounds/acre of 2,2-DPA. Spraying paraquat di (methyl sulphate) several days after first irrigation burned all vegetation, though a new germination of clover later occurred. Applied at rates from .25 to 1 lb./acre it controlled barley grass, especially at the higher rates. Diquat dibromide was also thought promising for the control of barley grass if applied as an early post emergence spray at 2 lb/acre. In field trials in 1980 to 1982 on cereal/pasture ley rotations, application of 300-450 ml glyphosate reduced populations of Hordeum leporinum, Bromus and Vulpia by up to 98%. These tests in southern Australia found that the optimum application was at the early head to milky dough stages of the grasses. The authors recommend that one day should allow for adequate adsorption and translocation of the herbicide. While the legume seed production was reduced, this was offset by increased legume vigor the following season due to reduced grass competition (Jones et al. 1984).
At the Plant Materials Center in Tucson, Arizona, Hordeum jubatum (foxtail barley) is controlled with Surflan, a pre-emergent herbicide. Foxtail barley can also be controlled with post emergent sprays that won't enter the soil and that are applied soon after the seedlings emerge (B. Munda, pers. comm.).
The introduced grass, Hordeum leporinum is a successful invader species, particularly where land has been disturbed (i.e. continuous grazing) and where soil nutrient levels are high and nitrogen rich. Under climatic conditions similar to the Mediterranean region (warm, dry summers and cool, moist winters that are relatively frost free), the species can become dominant over native plants.
Because the seed awn is often so damaging to stock animals, it is possible that the species could be harmful to wildlife as well.
Preserve Selection & Design Considerations:
No research is available on the recovery potential of land that has been overcome by Hordeum leporinum. Control has been achieved, however, through certain types of mowing, which decreases seed production and subsequent germination, as well as through herbicide applications.
As discussed previously in the Biology-Ecology section, mowing in Australia has been found to control barley grass, but the time and type of cutting must be adjusted so as not to replicate the effects that grazing can have on Hordeum leporinum. Some degree of control was achieved when the grass was cut close to the ground about ten days after the head started to turn color. The herbage was then removed. Native seeds could then be sown to further discourage establishment of barley grass. This treatment was most effective when repeated for one or two years, though there is little indication in the literature of precisely how many years of treatment would be required to completely eliminate barley grass; mowing in California was found to have only an immediate effect of eradication, with the grass returning the following year.
Some herbicides have proven effective in controlling barley grass when it has invaded alfalfa and clover fields. These include paraquat di (methyl sulphate), pronamid, 2,2-DPA, diquat dibromide and glyphosate. However, the literature describing applications dates from the 1960's in addition to two brief notes from 1986 (Squires 1963, Tickner 1968, McGowan 1970, Cudney and Orloff 1986, Orloff and Cudney 1986). More recent research, preferably on tests done in natural areas, is needed.
Color infrared aerial photography could be tested as a method of monitoring the general extent of Hordeum leporinum cover and of differentiating the species from other cool season annuals. Belt transects might also be useful as a more precise monitoring tool to detect changes in per cent cover over time (H. Richter 1990).
There are no known current monitoring programs.
Little research has apparently been conducted on Hordeum leporinum in natural areas. For instance, no information is available on which native species occupy the cool season annual niche before barley grass invasion. I know of no research on the prevalence, ecology, or control of barley grass in Arizona. More specifically, information is needed on how the habitat needs of barley grass differ from the Arizona native Sitanion hystrix, or why barley grass persists in place of native species after artificial disturbances have been eliminated (H. Richter 1990). The number of consecutive years of mowing or herbicide use that are necessary for complete elimination of barley grass must be determined for Arizona. The following needs are listed:
- Research conducted in pastures, on control in natural settings, and on restoration techniques.
- Prevalence, ecology and control methods of Hordeum leporinum in Arizona.
- How fire frequency and season affect growth of barley grass in Arizona.
The only extensive research on Hordeum leporinum has been taking place in southern and western Australia. Experts in Arizona know of no ongoing research in this country.
Biddescombe, E., E. Cuthbertson and R. Hutchings. 1954. Autoecology of some natural pasture species at Trangie, New South Wales. Australian Journal of Botany 2:69-98.
Briggs, T. 1990. Preserve Manager, Gray Davis/ Spike Creek Preserve, California. Telephone conversation with S. Dean, Nature Conservancy, Tucson, Arizonia, Dec. 13. (T. briggs referred to a Master's Thesis on prescribed burning in grasslands, written by Rob Hansen at California State University at Fresno in 1985 or 1986. Tom Briggs could copy and send the thesis. His phone number: 916-527-4261).
Campbell, R. and J. Beale. 1973. Evaluation of natural annual pastures at Trangie in central western New South Wales 2. Botanical composition changes with particular reference to Hordeum leporinum. Australian Journal of Experimental Agriculture and Animal Husbandry 13:662-668.
Carter E. 1987. Establishment and natural regeneration of annual pastures. In Wheller, J. C. Pearson and G. Robards, eds., Temperate pastures: their production, use and management. Commonwealth Scientific and Industrial Research Organization.
Chapin, F., R. Groves, and L. Evans. 1989. Physiological determinants of growth rate in response to phosphorus supply in wild and cultivated Hordeum species. Oecologia 79:96-105.
Cocks, P. 1973. Response to nitrogen of three annual grasses. Australian Journal of Experimental Agriculture and Animal Husbandry 14:167-172.
Cocks, P., K. Boyce and P. Kloot. 1976. The Hordeum murinum complex in Australia. Australian Journal of Botany 24:651-662.
Cocks, P., and C. Donald. 1973a. The germination and establishment of two annual pasture grasses (Hordeum leporinum Link and Lolium rigidum Gaud.) Australian Journal of agricultural Research 24:1-10.
Cocks, P., and C. Donald. 1973b. The early vegetative growth of two annual pasture grasses (Hordeum leporinum Link. and Lolium rigidum Gaud.) Australian Journal of Agricultural Research 14:11-19).
Covas, G. 1949. Taxonomic observations on the North American species of Hordeum. Madrono 10 (1):1-21.
Crampton, B. 1974. Grasses in California. University of California Press, Berkeley, California. 178 pp.
Cudney, D. and S. Orloff. 1986. Competitive effects of wild barley in seedling alfalfa. Research Progress Report of the Western Society of Weed Science. Western Society of Weed Science, 115-116.
Fitzgerald, R. 1976. Effect of stocking rate, lambing time and pasture management on wool and lamb production on annual subterranean clover pasture. Australian Journal of Agricultural Research 27"261-275.
Gould, F. 1951. Grasses of southwestern United States. University of Arizona, Tucson, Arizona. 343 pp.
Halloran, G., and A. Pennell. 1981. Regenerative potential of barley grass (Hordeum leporinum). Journal of Applied Ecology 18:805-813.
Jones, S., W. Blowes, P. England and P. Graser. 1984. Australian-weeds (Monsanto Australia Ltd.) 3:4, 150-151.
Kearney, T.H., and R.H. Peebles. 1951 (with supplement in 1960). Arizona Flora. Univ. California Press, Berkeley. 1085 pp.
Kriedemann, P. and J. Anderson. 1988. Growth and photosynthetic responses to manganese and copper deficiencies in wheat (Triticum aestivum) and barley grass (Hordeum glaucum and leporinum). Australian Journal of Plant Physiology 15:429-446.
McGowan, A. 1970. The effect of four herbicides on pasture yield and composition. Australian Journal of Experimental Agriculture and Animal Husbandry 13:398-403.
McGowan, A. 1970. The effects of four herbicides on pasture yield and composition. Australian Journal of Experimental Agriculture and Animal Husbandry 10:42-47
McIvor, J. and D. Smith. 1973. The effect of management during spring on the growth of a mixed annual pasture containing capeweed (Arcotheca calendula). Australian Journal of Experimental Agriculture and Animal Husbandry 13:398-403.
Moore, R. 1970. South-eastern temperate woodlands and grasslands. In Moore, R., ed., Australian Grasslands. Australia National University Press, Canberra.
Munda, B. 1990. Plant Materials Center, Soil Conservation Service, Telephone conversation with S. Dean, the Nature Conservancy, Tucson, AZ. November 30.
Myers, L. and V. Squires. 1979. Control of barley grass (Hordeum leporinum) by grazing management in irrigated pastures. Australian Journal of Experimental Agriculture and Animal Husbandry 10:151-155.
Ogden, P. 1990. Professor of range Science, Department of Renewable Natural Resources, University of Arizona. Telephone conversation with S. Dean, the Nature Conservancy, Tucson, AZ. September 7.
Orloff, S. and D. Cudney. 1986. Winter weed control in established alfalfa. Research Progress Report of the Western Society of Weed Science. Western Society of Weed Science, 96-97.
Parker, K. 1972. An illustrated guide to Arizona weeds. University of Arizona Press, Tucson, AZ.
Richter, H. 1990. Preserve Manager, Hassayampa River Preserve, Arizona. Memorandum to Dave Gori, The Nature Conservancy, Tucson AZ. Oct. 19.
Robards, G. and J. Leigh. 1968. The effect of frequency and time of cutting on the production and quality of a barley grass (Hordeum leporinum) dominant pasture. Australian Journal of Experimental Agriculture and Animal Husbandry 7:528-532.
Robinette, D. 1990. Cooperative Extension Agent, USDA, Soil Conservation Service, Tucson, AZ. Telephone conversation with S. Dean, the Nature conservancy, Tucson, AZ. Sept. 13.
Rosiere, R. 1987. An evaluation of grazing intensity influences on California annual range. Journal of Range Management 40 (2): 160-165.
Rossiter, R. 1964. The effect of phosphate supply on the growth and composition of annual type pasture. Australian Journal of Agricultural Research 15:61-76.
Rossiter, R. 1966. Ecoology of the Mediterranean annual-type pasture. Advances in Agronemy 18:1-56.
Sampson, A., A. Chase, and D. Hedrick. 1951. California grasslands and range forage grasses. California Agricultural Experiment Station Bulletin 724:3-130.
Smith, D. 1968a. The growth of barley grass (Hordeum leporinum) in annual pasture 1. Germination and establishment in comparison with other annual pasture species. Australian Journal of Experimental Agriculture and Animal Husbandry 8:478-483.
Smith, D. 1968b. The growth of barley grass (Hordeum leporinum) in annual pasture 2. Growth comparisons with Wimmera ryegrass (Lolium rigidum). Australian Journal of Experimental Agriculture and Animal Husbandry 8:484-490.
Smith, D. 1968c. The growth of barley grass (Hordeum leporinum) in annual pasture 3. Some factors affecting balance with subterranean clover (Trifolium subterraneum). Australian Journal of Experimental Agriculture and Animal Husbandry 8:702-705.
Smith, D. 1968d. The growth of barley grass (Hordeum leporinum) in annual pasture 4. The effect of some management practices on barley grass content. Australian Journal of Experimental Agriculture and Animal Husbandry 8:706-711.
Smith, D. 1972. Hordeum species in grasslands. Herbage Abstracts 42(3): 213-223.
Wallace, M. 1970. Insects of grasslands. In Moore, R., ed., Australian grasslands. Australian National University Press, Canberra.
Warr, G. 1981. Barley grass can lower sheep production. Agricultural Gazette of New South Wales 92(1): 27-28.