A. myosuroides is an annual grass which is native to Eurasia and grows in moist meadows, deciduous forests, and cultivated or disturbed ground. A significant weed species in temperate cereal crops, it has become one of the most damaging w...
A. myosuroides is an annual grass which is native to Eurasia and grows in moist meadows, deciduous forests, and cultivated or disturbed ground. A significant weed species in temperate cereal crops, it has become one of the most damaging weeds of winter cereals in Western Europe with the changes in agricultural practice over the past 30 years from regular ploughing to reduced tillage systems, suppression of broadleaf weeds in continuous cereals, and the move away from burning of stubbles. These changes have allowed the weed to invade well-drained lighter soils in addition to the heavier clay soils on which it is dominant. It has been introduced repeatedly as a weed of cultivation into many temperate and warm temperate regions but has not spread to a large degree out of cultivation. A. myosuroides has been listed as a noxious weed in the state of Washington, one of the states where winter wheat is a major crop. Due to its propensity to evolve resistance to herbicides it is a threat to the productivity of continuous cereal growing in high-input systems of temperate areas.
The genus Alopecurus consists of 29 species and is distributed in almost all non-tropical regions and, to a certain extent, in the alpine tropics with its main distribution in southwest Asia. Dogan (1999) recognized two subspecies of A. myosuroides distinguished by the appearance of awns. The subsp. myosuroides has 8-12 mm long awns that are exerted from the glumes. This is the common form of the species that is native and widely distributed in Europe, found in Central/South Asia and has been introduced to North and South America, and Australasia. The subsp. tonsus is either awnless or has short awns that are not exerted from the glumes. Distribution of the subsp. tonsus is restricted to Greece, Cyprus and Turkey.
A. myosuroides is a tufted, slender, annual grass, 10 to 80 cm high (Naylor, 1972). The culms are often geniculate and the base of the leaf sheath is often coloured purple. The glabrous leaves are 3-17 cm long, 2-8 mm wide and linear to lanceolate in shape with a membraneous ligule up to 5 mm long. In the absence of competition, each plant may produce over 100 inflorescences, but in competitive cereal crops 3-4 per plant is more common (Moss, 1990).
The inflorescence is a spike-like, dense, cylindrical panicle, 4-12 cm long and 3-6 mm wide, often tinged brown or purple. The common name 'black-grass' derives from the dark colouration shown by ripening heads, which contrasts with the cereal crop which is still green in early July (Thurston, 1972). The spikelets are 4-7 mm long, single flowered, sub-sessile, with a disarticulation below the glumes. The glumes are united at the base, with three green nerves, narrowly winged and ciliate on keels. The lemmas equal the glumes in length, and are 4- to 5-nerved, with a 5-8 mm geniculate awn from near the base. Palea absent.
The flowers are protogynous and characteristically allogamous. Enforced self-fertilization results in a variable amount of seed set. The dispersal unit is a spikelet (commonly called 'seed') consisting of a caryopsis with the lemma and glumes attached (Naylor, 1972). Typically each inflorescence will contain about 100 spikelets (Moss, 1983).
A. myosuroides is most often found in regions with oceanic to sub-oceanic climates (Holzner, 1981). A. myosuroides is a sub-cosmopolitan species that is suspected to have originated from the Mediterranean and subsequently spread throughout Europe and western Asia. It is less widespread in countries with a more continental climate (Himme and Bulcke, 1975).
This weed is mainly a problem in western Europe, where it is one of the most serious weeds of cereal-based rotations, especially in France, Germany, Belgium and England (Holm et al., 1997). In the UK it is most abundant where the mean July temperature exceeds 15°C (Thurston, 1972) and it is not usually recorded on land above 1,000 ft (Salisbury, 1961). The species is rare in Scandanavia, and is included in the Swedish Red List of endangered species (Ingelög et al., 1993). Farmers in the south of the country are concerned that this is a “new” winter annual that has become more troublesome in recent years. However, work by Milberg and Anderson (2006) has demonstrated that a northward spread is unlikely. The species is restricted by climate, producing smaller plants and few seeds in the north of the country. More generally abundance of A. myosuroides can be expected to be influenced by climate change. For example, models suggest a future of warmer, drier summers and wetter, warmer winters in eastern Scotland. This appears to indicate a climate increasingly similar to that current in eastern England where A. myosuroides is a particular problem. If this leads to an increasing trend to winter-based rotations grass weed problems such as A. myosuroides could become more significant. However the climate model, also suggests a reduction in importance in England and Scotland possibly related to the very dry summer predictions (Davies et al., 2007). Other studies have suggested that with climate change the occurrence of A. myosuroides will change at the margins of the distribution of wheat production in Europe. This could lead to a decline in southern Europe as conditions for wheat become less favourable (Knight and Wimshurst, 2005).
Although it occurs in many other parts of the world, including North America, Asia and Australasia, it not usually considered a major weed in those areas, except locally. In the Pacific North West of the USA, the species is considered a problem in winter cereals in four counties of Oregon and Washington (Aldrich-Markham, 1992). Elsewhere it appears relatively rare in the other 20 states where it has been recorded. There are few details of the distribution of this species in Russia, eastern Europe and Central Asia beyond listings in relevant floras.
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
There appears to be no information in the literature on when A. myosuroides was introduced to areas beyond its native range. The species has been present in USA from at least the early part of the twentieth century. Specimens in US herbaria date from 1914 in both Oregon and New Jersey. Specimens from other states are from later collections e.g. Alabama in 1966 and North Carolina in 1968 (GBIF, 2008) but these are no more than indicative. There is no indication of the origin of such infestations.
There is little discussion in the literature of the risk of further spread of A. myosuroides in areas to which it has been introduced or of further introduction, with the exceptions of the states of Oregon and Washington, USA. Extension literature from the region (Aldrich-Markham, 1992) indicates that because the species has an extremely high seed production capacity there is potential for further spread in winter cereal producing areas of the Pacific North West. These authors note that A. myosuroides which is currently confined to three counties in Washington and one in Oregon, sheds seed ahead of the crop harvest and is well adapted to cereal production practices. However, Lass and Prather (2007) report A. myosuroides as recently spreading from Whitman county in Washington into hay meadows, winter crop land and along roadsides into Latah county, Idaho.
A. myosuroides is abundant in cereal fields in England, France, Germany and many other European countries (Holm et al., 1997). Although the species occurs in a wide range of crops, it is mainly associated with cereal dominated rotations and its presence as a weed of arable crops is closely related to the frequency of autumn-sown crops, particularly cereals, in a rotation (Himme and Bulcke, 1975). The weed is most often found on heavy soils with a high clay content and good water retention capacity (Dunker et al., 2000) although this is partly an association with the cropping systems commonly adopted on such soils rather than an adaptation to a specific soil type (Brenchley, 1913). In England it remains chiefly confined to heavy land, occurring only occasionally on sandy or gravely soil but in recent years has begun to appear on chalk soils (Bond et al., 2007).
The species may also be found in hay meadows and spreading alongside roads as has recently been observed in Idaho (Lass and Prather, 2007). Here it is also associated with seasonally water-saturated soils of the Palouse Prairie. The prairie lands of the Palouse are less than 1% of the original size and the focus of many local conservationists.
Holm et al. (1997) report that A. myosuroides is a weed of 23 crops in 37 countries and is most important in European cereal-based rotations when they consider it to be as serious as Avena fatua (wild oat). Under these conditions the grass is a particular problem in winter wheat and barley, oil seed rape, field beans, potatoes, oats and rye.
Accessions of the grass that have been examined from different parts of the native range are diploid with 2n=14 chromosomes (e.g. Sieber and Murray, 1979). Morphological variability is seen even among plants present at the same site. Three plant types from a wheat field in Italy differed in panicle diameter and awn length, characters that showed high hereditability (Viggiani, 2005). Variability for other traits have been observed. Chauvel et al. (2002) demonstrated polymorphism for vernalization requirement both within and between populations.
Recent molecular studies have concentrated on the population variability in resistance to herbicides. Work in France showed no geographical structure to black-grass populations implying that these populations, although geographically distant, are, or have until recently been, connected by gene flows (Délye et al., 2004). The authors indicated that target site-based resistance to acetyl-coenzyme A carboxylase (ACCase) inhibiting herbicides results from the independent selection of various resistance mechanisms in local black-grass populations undergoing contrasted herbicide and agronomical selection pressures as different ACCase resistant alleles are found at different sites. Cavan et al. (1998) using genetic fingerprinting techniques showed evidence for evolution of resistance ACCase inhibiting herbicides in a number of patches of A. myosuroides in adjacent fields, patches that had plants that were genetically disimilar.
A. myosuroides is an annual grass which grows up to 80 cm tall. It propagates solely by seed: 50 to 6000 seeds per plant have been recorded (Holzner, 1981). With high infestations, over 50,000 seeds/m² may be produced and these are mainly shed prior to harvest of winter wheat crops (Moss, 1983). Most seeds have only a short period of innate dormancy (Barralis, 1968). As a typical winter annual, A. myosuroides shows a germination peak in the autumn with a second, smaller peak in the following spring (Wallgren and Avholm, 1978; Melander, 1992).
Germination is stimulated by light (Froud-Williams, 1985). Germination of A. myosuroides is not inhibited by abnormally low levels of oxygen in the soil, and may even be stimulated by them (Holzner and Namata, 1982). The seed bank in the soil shows an annual decline rate of 70-80% (Chadoeuf et al., 1984; Moss, 1985). Moss (1985) recorded seedbanks of over 50,000 seeds/m², so that even after several years without further seed return many viable seeds may remain.
Physiology and Phenology
Cool damp weather during the maturation of black-grass seed is thought to increase the dormancy level of the seed. After a cool damp summer germination may be protracted or delayed with more seedlings than is usual emerging after cereal drilling (Bond et al., 2007). In the field in UK, there are two peaks of germination, autumn and spring, but weather conditions in the autumn may delay germination until spring (Salisbury, 1961; Thurston, 1972). If conditions are favourable most seeds germinate in late October and early November (Thurston, 1964). There is then a small flush of seedlings in spring, which is increased if autumn germination has been prevented (Thurston, 1976).
In the UK, A. myosuroides flowers from May to August, sometimes into October (Morse and Palmer, 1925; Long, 1938). It is both self-fertile and cross-pollinated. The pollen is wind borne. The flower heads appear above the cereal crop in May and June. Flowering time is strongly influenced by vernalisation (Chauvel et al., 2002). While leaf and tiller appearance rate are increased at lower nitrogen levels and higher A. myosuroides densities, seed production is not strongly influenced by increasing nitrogen fertiliser application (Chauvel et al., 2005). Indeed Naylor (1972) demonstrated the ability of the weed to use nitrogen was reduced by competition with a crop and Chauvel et al. (2001) indicated little response in the field of A. myosuroides development, growth and seed production to nitrogen fertiliser doses.
No information has been found in the literature on the importance of natural enemies for the regulation of A. myosuroides populations. The weed is considered the most important alternate host of ergot fungus (Claviceps purpurea) in wheat in Europe (Mantle and Shaw, 1977).
Vector Transmission (Biotic) A. myosuroides seed has been found in cattle droppings (Salisbury, 1961). However, seed is rarely reported to survive passage through the digestive system of birds and other animals (Thurston, 1972).
Early records suggest that A. myosuroides was once planted as a forage grass but was refused by most cattle (Naylor, 1972). However, it is not known if the grass was taken beyond its indigenous range for use in pasture.
There are few reports in the literature about pathways for introduction and spread of A. myosuroides. There is evidence of contamination of crop seed. This could result in both local and long distance spread. The species sheds seed relatively early so reducing the likelihood of contamination of most cereals except winter barley (Froud-Williams, 1987). However, in a survey of weed seed contamination in cereal seed in drills ready for sowing on farm in UK in spring 1970, A. myosuroides seed was found in 3% of samples (Tonkin and Phillipson, 1973). All of these were home-saved seed. In the period 1978-1981, it was found in 16-21% of wheat and 3-14% of barley seed samples tested (Tonkin, 1982).
Separation of A. myosuroides seed from the seed of cultivated grasses can be difficult. MacKay (1964) found A. myosuroides seed occurred in 4 to 23% of grass seed samples examined in the UK particularly meadow fescue (Festuca pratensis). Seeds of the weed have also been found in perennial ryegrass (Lolium perenne), Italian ryegrass (Loliummultiflorum), cocksfoot (Dactylis glomerata), Timothy grass (Phleum pratense), red fescue (Festuca rubra) and tall fescue (Festuca arundunacea) samples (Gooch, 1963). A. myosuroides has also occurred as a contaminant of clover seed (Bond et al., 2007).
Although seed of the weed is usually shed ahead of cereal harvest there is clearly a possibility of longer distance transport of seed in baled straw moved by road to livestock producing areas. Spread within or between fields may occur in combine harvesters or cultivation equipment. Movement of seeds in soil is also likely to be important, both during cultivation and in soil attached to equipment or tractor tyres. The use of contractors may increase the risk of spread between farms. However on individual fields patches of the weed remain relatively stable in their positions over a long time-scale. Wilson and Brain (1991) found over a 10-year period that the grass exhibited little ability to spread to new areas but persisted in the established areas of infestation.
Wilson and Wright (1990) studied the growth and competitiveness of 12 annual weed species in crops of winter wheat. Species were listed in competitive order based on percentage yield loss per weed per m²: Avena fatua>Matricaria perforata>Galium aparine>Myosotis arvensis>Poa trivialis>Alopecurus myosuroides>Stellaria media>Papaver rhoeas>Lamium purpureum>Veronica persica>Veronica hederifolia>Viola arvensis. This showed that A. myosuroides is a moderately competitive weed on a per plant basis. However, very high populations of up to 1000 or more plants per m² can occur if uncontrolled, resulting in very high potential yield losses.
By the mid-1980s, A. myosuroides was already widespread in the UK infesting over 65% of fields in some regions and over 650,000 ha in the entire country (Roberts and Chancellor, 1986). Hurle (1993) ranks six grass weeds according to their importance. He considers A. myosuroides as the most important grass weed in Germany. It is highly important in winter cereals and oilseed rape, of medium importance in spring cereals and sugarbeet and of low importance in maize. Roder and Eggert (1990) measured yield losses of up to 15.6% in winter barley on a plot infested with 240 A. myosuroides plants per m².
Ingle et al. (1997) showed that the winter wheat yield loss caused by A. myosuroides varied considerably between sites. In a comparison of 11 field experiments in the UK, the weed density causing a 5% yield loss varied from 4 to 82 plants per m² with a mean of 24 plants per m². The economic threshold level for A. myosuroides in winter wheat and winter barley is 20-30 plants per m² (Zwerger, 1996). Lower longer-term thresholds (7.5 plants per m²) have been advocated as a means of preventing weed build-up (Doyle et al., 1986).
Despite the widespread use of grass herbicides, A. myosuroides is a very important weed in Europe. This is partly due to the ability of populations to increase rapidly, by over 10-fold per annum, if not effectively controlled (Moss, 1990). Grass weeds such as A. myosuroides have increased in most arable crops. The main reasons are: more autumn sown crops, especially cereals; increased use of reduced tillage systems; banning of straw burning; earlier sowing date; high nitrogen fertilizer use; and the development of herbicide-resistant populations (Hurle, 1993).
Resistance is now widespread in major winter cereal-producing areas of Europe to two main modes of action in widely used herbicides, both inhibitors of acetyl-coenzyme A carboxylase (ACCase) inhibiting herbicides (e.g, fenoxaprop) and acetolactate synthase (ALS) inhibitors (i.e. sulfonylureas including iodosulfuron-methyl sodium + mesosulfuron-methyl). Herbicide resistance complicates management of the weed and increases costs. In France target site- and non-target site-based resistance to ACCase inhibitors was detected in 99.2% of 243 A. myosuroides populations collected across the country. Mutant, resistant ACC allele(s) were detected in 56.8% of the populations (Delaye et al., 2007). Acetolactate synthase (ALS) target-site resistance conferred by a Pro,97 mutation has now being identified in England and is of concern because of increasing use of sulfonylurea herbicides such as mesosulfuron + iodosulfuron in Europe. There are also an increasing number of sites with A. myosuroides populations that have multiple resistance to a number of modes of action. These include resistance to ACCase, ALS, photosystem 2 inhibitors, ureas and amide and dinitro aniline based herbicides at the same site (see Weedscience.com, 2008).
The impact of A. myosuroides on biodiversity is rarely mentioned in the literature. Concern has been raised however over invasion of the Palouse Prairie in Idaho (Lass and Prather, 2007). The prairie lands of the Palouse are less than 1% of the original size and the focus of many local conservationists.
In comparison with A. myosuroides, the perennial Alopecurus pratensis has a broader panicle, noticeably hairier margins to the spikelets and a shorter ligule. A. pratensis occurs mainly in pasture (commonly planted in wetter areas in the north-west USA (Aldrich-Markham, 1992) and hedgerows whereas A. myosuroides is primarily a weed of arable land. Alopecurus geniculatus is a shorter plant and occurs in wet or moist places and is rarely seen in arable situations. Alopecurus aequalis, a weed of rice and cereals in lowland areas of several temperate regions, particularly China, Japan, Nepal and Philippines (Holm et al., 1997) also has dense spike-like awned panicles. This species is also known from USA. The distinguishing features are the bright orange anthers, the short awn which is almost hidden, extending 1 mm or less from the glumes and the long hairs on the glumes.
A. myosuroides often occurs in mixed populations with Apera spica-venti in central Europe, but is easily distinguished by the open panicle of the latter species.
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
A. myosuroides is scheduled as a Class B noxious weed in Washington State, USA. As such, land owners are obliged to undertake control operations in defined areas of the state.
Early warning systems
None are known for this species.
There are no reports of eradication attempts
Cultural control and sanitary measures
The growth cycle of A. myosuroides is well adapted to autumn sown crops. Seedling emergence occurs at the same time as the crop, so the weed is not at a competitive disadvantage, and most seeds are shed prior to harvest, so are not removed with the harvested crop. Because it is competitive and populations have the ability to increase rapidly, it has to be controlled regularly. Cultural control measures can have a big impact on populations but herbicides are the main means of control (Hurle, 1993). High levels of control are needed in order to prevent populations increasing (Moss, 1990).
Many non-chemical methods are available for controlling A. myosuroides, but the levels of control achieved tend to be variable and unpredictable. Non-chemical control methods are unlikely to totally replace herbicides in intensive cropping systems, but can be considered complementary and have the potential to reduce herbicide use. However these are vital to organic growers and options have recently been reviewed by Bond et al. (2007).
Crop rotation, tillage and sowing time are three elements of a production system with potential as indirect measures for the control of annual weeds (Chauvel et al., 1998).
Growing crops that are unfavourable for a particular weed will lead to lower infestation and therefore to a quick decline of the seed bank in the soil.
The presence of seeds shed in the previous crop greatly influences A. myosuroides infestation in direct drilled crops where it was calculated that 80–90% of plants were derived from these recently shed seeds. In the crop established after ploughing, the infestation was unaffected by seed production in the previous crop (Moss, 1980). This study also demonstrated that straw burning destroyed many freshly shed seeds on the soil surface and resulted in less A. myosuroides in the crop. However, the practice of burning became socially and environmentally unacceptable and is no longer used in much of Europe. Ploughing buries seeds for one season; their chances of germinating and emerging are drastically reduced until they are returned to the topsoil in the next year (Hurle, 1993). The adoption of reduced tillage is viewed as a major reason for the present problems in controlling grass weeds such as A. myosuroides (Hurle, 1993). Methods of straw disposal that involve minimal cultivations will normally result in a build up of A. myosuroides particularly on heavy soils (Turley et al., 1996). Rotational ploughing, one year in three, will help to keep the grass in check but if an infestation is allowed to reach an excessive level, annual ploughing may be required for several years running.
The trend to early sowing of winter wheat, commonly now in late-September/mid-October in Europe, leads to severe infestations. This is both because the crop becomes established during peak emergence of A. myosuroides, and because the weed has time to become fully tillered before winter (MAFF, 1975). Sowing cereals before 25 October has been shown to increase A. myosuroides infestations, sowing after 5 November has led to a decrease (Bond et al., 2007). However, although emerged seedlings can be destroyed by seedbed preparation techniques linked to delayed sawing there may be may be a substantial loss in yield if winter wheat is drilled after mid-November.
In winter wheat the choice of cultivar and sowing rate can have a marked effect on A. myosuroides panicle numbers (Blake, 2006). Cultivars that tiller well and achieve an early ground cover reduce A. myosuroides head numbers the most and the effect is greater at high seed rates.
In summary, for A. myosuroides, Hurle (1993) states that “crop rotations with a high proportion of spring crops and ploughing as the tillage system are not likely to run into serious problems with this grass weed”. However, spring crops are often less profitable than autumn-sown crops and many farmers throughout Europe are seeking to replace ploughing with reduce tillage systems in order to reduce costs. Thus the threat from A. myosuroides is tending to increase rather than decrease.
Mowing frequency can be adjusted to suppress the weed in non-crop areas. Mowing is being used successfully on road verges in Idaho (Lass and Prather, 2007).
No measures to control movement of the species are reported.
No biological control agents have been developed for use against this species.
Many products have been introduced over the past 40 years that when first used provided effective control of A. myosuroides The most often-used herbicides are the substituted ureas, aryloxyphenoxypropionates, cyclohexanediones, dinitroanilines and sulfonyl-ureas (Schmidt, 1997).
Chlorotoluron and isoproturon are substituted ureas which show activity against other grass and broad-leaved weeds and are mainly soil acting herbicides. Their broad spectrum of activity has led to an intensive use of these herbicides, mainly as autumn treatments of winter cereals (Hance and Holly, 1990). Resistance to this class of chemistry has evolved at a number of sites (e.g. Hall et al., 1995). Isoproturon will not be registered for use after 2008 in Europe due to environmental concerns. However, Laux et al. (2006) consider that chlorotoluron will still have an important role to play in A. myosuroides management in Germany. Fenoxaprop-P-ethyl and clodinafop-propargyl are two aryloxyphenoxypropionate herbicides widely used in wheat crops, and fluazifop-P-butyl and propaquizafop are members of the same herbicide class used in broad-leaved crops such as oil-seed rape. Resistance to this class of herbicides in A. myosuroides in Europe is now common (Delye et al., 2007).
The cyclohexanedione herbicide tralkoxydim is used in cereals and cycloxydim and sethoxydim in broadleaved break crops. The dinitroaniline herbicides trifluralin and pendimethalin have often been used in mixtures with other herbicides for control of A. myosuroides. However trifluralin is due to be withdrawn from the market in Europe in 2009, due to health and environmental concerns. Flupyrsulfuron is a recently introduced sulfonyl-urea herbicide for use in wheat.
Other herbicides, such as tri-allate, imazamethabenz-methyl and terbutryn are used in cereals and propyzamide and metazachlor in broad-leaved break crops.
Repeated use of herbicides led to the development of herbicide resistance in England and Germany in the early 1980s. Resistant populations now occur in nine European countries. One UK case study estimated that the cost of herbicide resistant A. myosuroides in winter wheat is $300/ha while the cost of preventing resistance is $146/ha (Orson, 1999).
Use of the cell division inhibitor flufenacet has increased in popularity as an autumn applied pre-emergence treatment for A. myosuroides. No resistance had been reported by June 2008. Due to relayed emergence of the weed it is common to follow flufenccet with post-emergence mesosulfuron methyl + iodosulfuron methyl applied in the spring. However there are increasing concerns of resistance developing to the ALS inhibitor (Weedscience.com, 2008).
A system of digital image analysis has been developed that can identify seeds of A. myosuroides in cereal samples (Sokefeld et al., 1999). This can be used to analyse the purity of crop seed or grain samples.
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