G. maxima is an aquatic, perennial grass, which is native to temperate Europe and Asia, and an invasive species in New Zealand, Australia and North America (USDA-ARS, 2009). In the USA, it is listed as prohibited in Massachusetts and potentially invasive in Connecticut (USDA-NRCS, 2009).
G. maxima spreads vigorously from rhizomes and seedlings that produce numerous vegetative and flowering shoots. A single plant may produce up to 100 shoots and 30 m of rhizome in its first 2 years of growth (Parsons and Cuthbertson, 1992).
Dense stands of G. maxima severely impede water flow in canals and streams, often causing local flooding and livestock to become bogged down and drown (Barton et al., 1983). It also causes accelerated siltation resulting in a reduction of the holding capacity of farm dams (Parsons and Cuthbertson, 1992). The ability of this vigorous invader to create monocultures is of conservation concern even in its native range (Lambert, 1947).
Glyercia is from the Greek glykeros, meaning ‘sweet’, and refers to the sweet taste of seeds from some species. Maxima is the superlative of the Latin magnus, meaning ‘great’ or ‘large’, inferring that this species is the largest in the genus (Parsons and Cuthbertson, 1992). A cultivar G. maxima 'Variegata' is grown in North America.
G. maxima is a robust, leafy, aquatic, perennial grass that grows 90-250 cm high, with numerous vegetative shoots. Seeds germinate in spring and seedlings develop rapidly producing many vigorous shoots as well as a mat of creeping rhizomes in summer and autumn that contribute to spread beyond their periphery. During winter growth slows or ceases and then recommences in spring when both vegetative and flowering shoots are formed.
Leaves glabrous, bright green, sometimes tinged with red when young, especially in the sheath. Sheaths predominantly cross-veined, distinctly keeled distally and broadly naviculate in cross section. Ligule membranous, 3-6 mm long, entire or slightly divided, truncate, but usually with a central point. Blade abruptly pointed, 30-60 cm long, 7-20 mm wide, rough on the margins and sometimes the lower surface.
Inflorescence a loose, later dense, oblong many branched panicle, 15-45 cm long. Spikelets yellow or green tinged with purple, slightly compressed, stalked, oblong, 5-12 mm long, 2-3.5 mm wide and 4 to 10 flowered.
Seed dark brown, 1.5-2 mm long, enclosed in persistent, hardened flowering glumes. Glumes unequal, lower 2-3 mm, upper 3-4 mm, membranous, usually obtuse. Lemmas 3-4 mm long, not keeled, but with usually seven very prominent nerves. Paleas equal to lemmas or slightly shorter, boat shaped, flanges scaberulous. Lodicules fairly large, more or less connate, though generally separable. Stamens 3, anthers up to 2 mm long, yellow or purple. Styles 2, appearing to arise laterally; naked proximally, branched distally.
Root fibrous, 1-2 mm diameter, several arising from each rhizome node, extending to depths of 1 m and giving raise to laterals 1-8 cm long (Lambert, 1947; Parsons and Cuthbertson, 1992).
G. maxima is native to the north temperate zone of Europe and Asia. It is found as far eastward in Asia as Japan and the Kamchatka Peninsula(Anderson and Reznicek, 1994;USDA-ARS, 2009). Several references (DPIWE, 2009; ISSG, 2009) cite that G. maxima is invasive in the UK; however, Lambert (1947) claims that it is native flora of the UK. Additionally, Stace et al. (2009) states G. maxima is “common in most of England except North, scattered in Wales, Ireland and Scotland, 1 record in Guernsey, not in North or Northwest Scotland.”
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.
G. maxima was widely distributed on a commercial scale in Australasia by rootstock planting in the early twentieth century (Lambert, 1947). Allan (1940) gives 1904 as the date of the first printed records of its occurrence in New Zealand. Commercial planting saw G. maxima establish in various locations (notably Otago and Southland) on both the North and South Islands, where it spread sufficiently to block waterways (Allan, 1940). The original source of G. maxima in Australia was a few plants in Victoria grown from English seed. It rapidly became established in Victoria, New South Wales, Tasmania and Western Australia where it proved vigorous enough to out-compete indigenous swamp vegetation in suitable habitats (Brown, 1929). It was later recorded in Queensland (CPBA, 2009). A limited number of planting experiments made in tropical Australia and New Guinea proved unsuccessful (Brown, 1929).
Introduced from Australia to a few places in South Africa, but limited planting experiments have indicated that G. maxima does not flourish or spread nearly as rapidly as reported for Australia, the results being insufficient to warrant further trials (Lambert, 1947).
The first occurrence of G. maxima in North America dates from 1940 and comes from a marsh at the edge of Lake Ontario. Between 1940 and 1952 several more populations of this plant were located in the same region, but it is possible that G. maxima arrived some time before these records were documented. The first record of G. maxima in New England is from the Ipswich River Wildlife Sanctuary in Essex County, Massachusetts in 1990 (IPANE, 2009). In North America, it is now found in southern Canada, primarily in Ontario, but also Newfoundland, British Colombia, and in the USA in Alaska, Wisconsin and Massachusetts (Dore, 1947; Reed, 1987; USDA-NRCS, 2009).
In Australia, all wetlands, shallow water bodies and the edges of rivers and creeks along the south-eastern coast and south-western corner of Australia have the potential to be invaded wherever the characteristics of the site are suitable (Loo et al., 2009a). In the USA, G. maxima is not currently present in Connecticut, but it is listed as ‘potentially invasive’.
However, dispersal pathways and vectors must be present to spread G. maxima into new regions where habitat is potentially suitable and it is difficult to estimate the time needed for this to occur. Deliberate introductions of the plant as a fodder are still possible, and accidental movement on machinery and animal hooves is a possibility. Seeds are available by mail order from the native range (Seeds-by-size, 2009). Both nursery stock and seeds for sowing are permitted into Australia (AQIS, 2009).
Wet or occasionally winter-flooded freshwater areas along banks of slow-moving rivers, creeks, canals, drainage ditches, lakes, wetlands, ponds and farm dams, principally in temperate regions. It grows well in water up to 75 cm deep and satisfactorily even at depths of 1.5 m. In deeper water it often forms floating mats which remain attached to the banks of streams or ponds (Parsons and Cuthbertson, 1992).
In its native range, G. maxima is found growing from the lowlands up to high altitudes in the mountain areas (Peeters, 2005). Lambert (1947) suggests that “these plants are typically a freshwater species and found in the bank of slow-flowing rivers. Exhibits a considerable vertical range in relation to water level, occur vigorously both as a reed swamp plant with roots and rhizomes immersed throughout the year. However, the presence of higher internal concentration of oxygen in the roots suggests for an immediate diphenylamine tests made on soil samples containing root fragments. Reaches best development both vegetatively and in production of flowering stems, in regions where summer water table is approximately at substrate level. When growing among other tall reed swamp species, they may produce excessively long vegetative stems. At the same time they are largely limited or excluded by the mechanical conditions of the habitat, where a diurnal tidal rise and fall of 20-30cm is combined with a loose, shifting substrate. These plants are found in fully exposed situations but are tolerant to slight shade”.
Reproduces by seed and rhizomes. Seeds germinate in spring and seedlings develop rapidly producing many vigorous shoots. Seeds are produced in the plants second and subsequent years. Flowering occurs in spring and summer and vast amounts of seeds are produced. These seeds have varying levels of dormancy, with the majority of seeds able to germinate immediately, whilst others are genetically bound to remain dormant for several years (Parsons and Cuthbertson, 1992; DPIWE, 2009). Only 1-9% of the florets set good grains (Dore, 1953 in Anderson and Reznicek, 1994) and the dense cover of the matted weed also hinders the establishment of seedlings (Weiss and Iaconis, 2000).
A mat of creeping rhizomes spreads in summer and autumn. During winter growth slows or ceases and then recommences in spring when both vegetative and flowering shoots are formed. A single plant may produce up to 100 shoots and 30 m of rhizome in its first 2 years of growth. The extensive root system of G. maxima can extend to depths of 1 m. A sprawling mass of rhizomes comprise 40-55% of the plant’s total biomass. These rhizomes produce vast numbers of shoots to quickly expand the plants size (DPIWE, 2002). Plants in mature stands grow considerably slower and those in deep water, with a more anaerobic substrate, grow even more slowly and have reduced rhizome development (Parsons and Cuthbertson, 1992).
In a mesocosm experiment by Tanner (1996) it was found that shooting density increased linearly during the first 90 days of the trial, then rose sharply during the remaining 30 days of the trial, more than doubling the shoot number. A very high above-ground biomass production (3.3 kg m-2 ) was also found.
Buttery and Lambert (1964) examined the competition between G. maxima and Phragmites communis in the Surlingham Broad, England, UK. They found that where G. maxima shows maximum growth, P. communis is completely suppressed. The success of G. maxima over P. communis under such conditions appears to be due to its rapid production of an extremely dense sward in spring, before the P. communis shoots can develop. However, at the back of the fen away from the open water, P. communis was more successful than G. maxima, indicating that it has somewhat greater tolerance to the unfavourable habitat conditions.
G. maxima is tolerant of waterlogging, fire and frost and of a wide range of climatic conditions, but prefers cooler, temperate regions (Weiss and Iaconis, 2000). It can establish in minor disturbed ecosystems of permanent and seasonal wetlands.
Haslam (1978) states the nutrient requirements (p.p.m.) of G. maxima are:
Nitrate-nitrogen: Poorly correlated
Ammonia-nitrogen: Poorly correlated
Phosphate-phosphorus: Below 1
G. maxima is more likely to be found on soils high in total phosphorus and nitrogen (Loo et al., 2009a). Haslam (1978) found that the grass was phosphorus limited, so it will spread only into areas with adequate phosphorus levels. G. maxima is only tolerant of light shade (Lambert, 1947; Loo et al., 2009b).
Existing colonies use their creeping rhizomes to spread beyond their periphery. Other dispersal mechanisms are by seed moved in flowing water or vegetative shoot movement during flood events. G. maxima seed is not readily dispersed by wind (Parsons and Cuthbertson, 1992; DPIWE, 2009).
In its natural range G. maxima can be readily consumed by cattle and is considered a nutritious fodder. However, in southeastern Australia and New Zealand it accumulates toxic levels of hydrocyanic acid which has resulted in the cyanide poisoning of livestock (Barton, 1983; Parsons and Cuthbertson, 1992). In South Gippsland both beef and dairy cattle deaths in spring have been attributed to G. maxima. Cyanic compounds are highly present in the vegetative tillers of the plant, only slightly in the flowering culms and not in the seeds (Barton, 1983). Additionally, Sharman (1968; cited in Barton 1983) found that the cyanide content of G. maxima varied greatly with season, peaking in spring when the grass was growing fastest and rising again in autumn. Given that G. maxima is not a preferred fodder source in Australasia, infestations result in a loss of area for nutritious fodder. Livestock have also become bogged down and drowned when attempting to reach water through dense infestations (Melbourne Water, 2003).
G. maxima can adversely affect water quality by making the water putrid and unusable. Farmers have had to relocate pumps after infested springs become polluted and cattle refuse to drink the water (Melbourne Water, 2003).The holding capacity of farm dams can be significantly reduced due to siltation. In dense stands it severely impedes water flow in canals, drainage ditches and streams, often causing local flooding (Parsons and Cuthbertson, 1992). There can be significant costs to landholders and waterway managers trying to control G. maxima using either chemical control or mechanical removal.
G. maxima has been likened to an autogenic ecosystem engineer, with the ability to impede water flow and convert fast-flowing aerobic streams into partially anaerobic swamps (Clarke et al., 2004). The formation of thick rhizomatous root mats is the likely mechanism by which G. maxima traps sediments and alters the stream habitat (Sanity and Jacob, 1994). Dense stands of G. maxima severely obstruct water flow in canals, drainage ditches and streams, often causing local flooding (Parsons and Cuthbertson, 1992). Hence, aquatic ecosystem function, including sediment and organic matter retention and nutrient dynamics, may be drastically affected (Clarke et al., 2004).
Impact on Biodiversity
The ability of this vigorous invader to create monocultures is of conservation concern even in its native range (Lambert, 1947). The spread of G. maxima in England, UK, reduced the number of seed-producing plants (particularly of the Cyperaceae and Polygonaceae) available to winter feeding ducks. G. maxima is reported to be a poor food plant for grazing waterfowl and a poor nesting substrate for many common wetland species (Burgess et al., 1990). Native to parts of Sweden but also occurs in areas where it is non-indigenous. In its introduced range it is seen to form dense stands which impact on native vegetation (Larson, 2003).
Impacts of G. maxima on native biota and ecosystems in the invaded range are poorly explored, but Clarke et al., (2004) found that streams invaded by G. maxima in S. Australia had lower compositional diversity of stream macroinvertebrates, with a shift from ‘shredders’ to ‘collector/filterers’.
In New Zealand, Taylor and Kelly (2001) found that G. maxima is proving to be a national threat to the whitebait (Galaxias maculatus) spawning grounds. G. maxima does not provide the right kind of micro-habitat required for whitebait spawning as the weed clogs waterways and has displaced tall fescue grass from riparian zones which would have been suitable spawning grounds.
G. maxima is unlikely to have any serious affect on cultural heritage sites, but dense infestations may have a negative visual effect, ruining the aesthetic appeal of waterbodies.Clarke et al. (2004) recorded that G. maxima may convert sections of fast-flowing streams into anaerobic, swampy environments. Such a dramatic change could affect recreational fishing as downstream fish habitat would be significantly affected by reduced water flow. Dense infestations may also diminish recreational opportunities as swimming, boating, fishing and other recreational activities may be restricted.
In its natural range G. maxima can be readily consumed by cattle and is considered a nutritious fodder. G. maxima was commercially planted in its invaded range as a ponded pasture grass in and around farm swamps, dams and streams (Walsh, 1994).
G. maxima is similar to Glyceria grandis, the American mannagrass, which is native to North America (IPANE, 2009). Dore and McNeil (1980) provide one of the few keys among North American manuals which distinguishes G. maxima from G. grandis. They separate G. maxima by the length of the lower glume (2-3 mm versus 1.2 -1.5 mm in G. grandis). It is distinguished from other European species by its firmly erect stems. Others are generally decumbent and/or submerged.
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.
Appropriate legislation is required to prevent the spread of G. maxima into susceptible areas. However, unless G. maxima is listed appropriately (e.g. as a declared or restricted weed), it will not fall under legislative restrictions.
Forecasts of the potential distribution of G. maxima can help to identify areas susceptible to invasion. The forecasts can inform decision-making for prevention schemes and assist targeted field sampling for the development of monitoring programmes and allow prioritization of control methods. Forecasts of the potential distribution of G. maxima in Australia have been undertaken by Loo et al. (2009a) and Weiss and Iaconis (2000). In New Zealand, the government is establishing a border control programme for aquatic plants that have the potential to become ecological weeds in New Zealand. The programme includes weed risk models that incorporate forecasts of the potential distribution, and an Aquatic Plant Weed Risk Assessment Model (Champion and Clayton, 2000, 2001).
Loo et al. (2009) found that the presence of G. maxima was negatively correlated with the amount of woody riparian vegetation. Riparian shading limits the spread and abundance of aquatic macrophytes, and G. maxima is only tolerant of light shade (Lambert, 1947; Bunn et al., 1998). Hence, the policy and management actions to maintain or restore riparian zones are likely to assist in the prevention of the spread of G. maxima.
The prevention of aquatic weed spread is the responsibility of all individuals and groups. Examples of prevention methods:
· Drainage contractors - ensure any weed is removed from machinery before moving to other waterbodies and waterways
· Fishermen and eelers - remove all fragments of weed from nets before leaving the area
· Boat operators - check boats, motors and trailers for tag-along weeds immediately on removal of equipment from the water
· Aquarium owners - don’t dispose of aquarium contents into or near a waterway
· Duck shooters - check dogs, boots and boats for weed before leaving the area
· Landowners - don’t allow drainage equipment, nets or boats into waterbodies on their property unless they are free of weeds (DOC, 2009).
Increased community awareness of the issue will be essential for successful control of aquatic weed species. The “Clean, Check, Dry principles” should be promoted to all users of waterbodies (DOC, 2009).
Early detection and confinement of new satellite populations are crucial, and will be possible only through targeted monitoring, and these monitoring systems need to be implemented using designs that recognize multiscale relationships (Mack, 2000; Olckers, 2004). A community-based weed detection network could play an important role in the early detection of new populations.
Mechanical removal, such as excavation or hand pulling, can be used to control G. maxima, but may be ineffective if the entire rhizome system is not removed (Parsons and Cuthbertson, 1992). Manual removal works best with small plants. Excavation is not a preferred management approach for waterways because using heavy equipment may damage the structure of the waterway (Weiss and Iaconis, 2000). Excavation is more suitable for use on farm dams and can be useful at reducing the size of large infestations, allowing easier follow up by manual removal of small plants and regrowth. Excavated material should be dumped well away from the area at a site where it can dry out and kill all plants.
Black plastic used to smother the grass was 100% effective in Massachusetts, USA. However, this method is not feasible over large areas (Rawinski, undated, in Martin, 2009). Cutting may reduce populations of reed sweet-grass by allowing sunlight to reach other, competitive plants. Multiple cuttings (more than three) may reduce the amount of carbohydrates stored in the rhizomes. Cutting during the autumn months when carbohydrates and nutrients are stored for the winter may affect spring regrowth (Sundblad and Robertson, 1988).
G. maxima can be almost controlled or in some instances completely eradicated using herbicides, such as glyphosate or dalapon, which are translocated through all parts of the plant. Trials in Tasmania, showed G. maxima was eradicated by glyphosate when applied in autumn, and was almost completely controlled by dalapon 5 and 10 kg/ha + paraquat (Tasmanian Department of Agriculture, 1976). In the UK, glyphosate applied in summer and autumn gave almost total control (Barrett, 1976). In Holland, the application of dalapon + Amitrol-T (aminotriazole + ammonium thiocyanate) and glyphosate in early autumn completely killed the foliage, although glyphosate was slower acting (Stryckers and van Himme, 1974).
When using herbicides on G. maxima, a complete coverage of all foliage is necessary. Care must be taken in choosing and applying herbicides near waterways as to not impact upon the resident organisms (DPIWE, 2009). The glyphosate-based Roundup bioactive™ is the recommended herbicide because it is safe for use in or near waterways (Caffrey, 1996). Glyphosate should be applied in late summer and autumn, when the plants are in full flower. Where practical, the water level should be lowered to maximise plant exposure before treatment (Paterson and Cuthbertson, 1992; DPIWE, 2009).
However, chemical controls can have disadvantages. The mass of decaying vegetation that remains after treatment reduces the holding capacity of the waterway and the anaerobic decomposition of the material may render the water foul and unfit for use. In such cases mechanical removal of the plant material will be required. The disturbed space created after treatment provides ideal conditions for invasion by other weeds or by a re-infestation of G. maxima.
G. maxima is sensitive to shade and appears to be out-competed once there is adequate cover of overstorey vegetation. The restoration of native riparian vegetation may be an effective long-term means of controlling invasive aquatic macrophytes, such as G. maxima.
Aquatic weed management requires an integrated catchment approach that recognizes the role that anthropogenic environmental change (such as the removal of riparian vegetation and increased soil nutrient content) has played in the spread of aquatic weed species (Loo et al., 2009a).
Greater information on the ecological impacts of G. maxima in the invaded range is required.
There is limited information on the impacts of G. maxima on waterfowl from its native range and none from the invaded range. There is only one study on the impacts on macroinvertebrates (from Australia) (Clarke et al., 2004) and only one study on the impact on fish (from New Zealand) (Taylor and Kelly, 2001).