Paspalum vaginatum
(seashore paspalum)

Paspalum vaginatum, commonly known as seashore paspalum and by many other names, is a species of perennial grass which can be found in wet, saline habitats. Reported to have originated from the Americas, it can be a serious weed of rice in West Africa. In coastal habitats, it can spread at 1-2 m per year and become dominant over native vegetation. In New Zealand, it is of concern having invaded the nesting areas of the endangered New Zealand fairy tern (Sterna nereis), threatening a range of uncommon or endangered plant species, and possibly affecting fish breeding. PIER (2016) assesses it as a 'High Risk' species (score 7) for the Pacific islands and confirms it as invasive in Hawaii (on golf courses) and the Marshall Islands, also on Diego Garcia in the Indian Ocean. In Spain it is classed as a species with ‘clear invasive behaviour; dangerous (causing ecological damage or alteration) for natural ecosystems’ (Dana et al., 2007). Similarly it is regarded as a threat to native vegetation in California, USA (Riefner and Columbus, 2008).

P. vaginatum is generally believed to have originated in the Americas, though Chen et al. (2005) studied the range of genetic diversity and concluded that its origin could be in Africa. ISSG (2016) indicated it is native only in USA and Ecuador and introduced everywhere else, but Lansdown et al. (2013) and most other sources now consider it to be native not only throughout the Americas and Africa but also in much of Asia (including Australia), and introduced to Europe, northern Africa, the Azores, New Zealand, Hawaii and Fiji. In the Pacific, PIER (2016) indicated it is native across many islands but definitely introduced to others, including Hawaii. It is widely grown as a turf grass and almost certainly occurs in many areas where it has not necessarily naturalized, such as some provinces of China.

P. vaginatum is not likely to be introduced accidentally but there is some risk of intentional introduction as a turf grass, as forage or for soil binding and soil remediation in coastal areas.

P. vaginatum is almost invariably associated with wet, saline conditions whether coastal or inland. It is found in coastal salt marshes of the tropics and sub-tropics. On various islands in the Pacific region, P. vaginatum is found in coastal sunny areas, near beaches and sometimes on the beach, in brackish marshy areas and mangrove swamps (PIER, 2016). It is best suited to compacted inorganic marsh soils of moderate salinity and is tolerant of drought, salt, a wide range of soil pH, extended periods of low light intensity, and flooding or extended wet periods (ISSG, 2016). In New Zealand, P. vaginatum grows on the open coast, but is most widespread in sheltered estuaries, lagoons and creeks that are influenced by tidal fluxes. It is found in coastal, often brackish areas. It often forms swards near the edge of mud flats, or on sandy and shingly shores, occasionally spreading into pasture nearby. It grows on estuarine mudflats, fine gravel, silty sand, sand; and in dryer situations above the high tide mark along exposed rocky coastlines, in crevices or beside brackish pools. It is not known inland (Graeme and Kendall, 2001).

In many regions, P. vaginatum is a serious weed of rice, especially in saline and brackish soils (Bernard, 1988; Terry, 1981).

Genetics

According to IPCN (2016), the chromosome number of P. vaginatum is 2n=20, but Lonard et al. (2015) report that tetraploidy (2n=40), hexaploidy (2n=60) and aneuploidy (2n=18) may also occur.

A range of 69 accessions of P. vaginatum showed three main genetic clusters. Those from Hawaii showed the least variability and those from Africa the highest, with those from North America intermediate (Chen et al., 2005).

A comprehensive transcriptone analysis has been reported by Jia et al. (2014). A total of 81,220 unigenes containing 8,7542,503 bp sequence information were formed by initial sequence splicing, with an average read length of 1,077 bp.

Reproductive Biology

Seed viability is apparently low and few were found in a seed bank in a densely-infested site in Lousiana, USA (Lonard et al., 2015). This may be partly attributed to the self-incompatibility reported by Carpenter (1958), who found that only one of four Australian and South African populations studied was self-fertile. Lonard et al. (2015) reported that a germination rate of less than 5% at room temperature was improved by a constant 35°C temperature or by an alternating temperature regime of 25°C to 35°C. Shin et al. (2006) and Shim et al. (2008) also found alternating 25/35°C to be optimal, together with KNO₃, but also found benefit from light. Serena et al. (2012) report that germination is unaffected by salinity levels up to 12.5 dS.m^-1.

Physiology and Phenology

P. vaginatum has C₄ photosynthesis.

Shonubi (2010) describes how P. vaginatum is able to accumulate salt in older leaves and store water to keep salinity to tolerable levels in the younger ones – not demonstrated in the related Paspalum scrobiculatum. Liu et al. (2012) conclude that the high salinity tolerance in P. vaginatum could be associated with a high abundance of proteins involved in ROS detoxification and energy metabolism.

Sexual reproductive phases occur during the summer, autumn and early winter throughout southwest USA.

P. vaginatum Flowers and fruits from June to September (Flora of China Editorial Committee, 2016).

Longevity

No specific information has been seen but established swards are likely to persist for many years. No information on seed longevity has been found.

Nutrition

In studies in Egypt, P. vaginatum was highly responsive to nitrogen as nitrate (but not as ammonium), showing increased growth up to the maximum 17.5 g/m² (El-Maadawy et al., 2006). For turf, the optimal dose of nitrogen is about 150 kg/ha per annum (Gates, 2003; Shadow, 2016). However, P. vaginatum is also tolerant of infertile conditions.

Associations

Lonard et al. (2015) provide extensive lists of species associated with P. vaginatum in a range of territories in North and South America and in West Africa. They also note that there is commonly an association with arbuscular mycorrhizal fungi. Garcia and Mendoza (2008) further confirmed that greatest arbuscular colonization was associated with the highest nitrogen and phosphorus concentrations in plant tissue, suggesting a correspondence with increases in the rate of nutrient transfer between the symbiotic partners.

Graeme and Kendall (2001) also describe a wide range of plant associations in New Zealand including mangrove, saltmarsh and backswamp communities involving Juncus krausii subsp.australiensis, Leptocarpus similis (Apodasmia similis), Sarcocornia quinqueflora, Suaeda novae-zealandiae, Samolus repens, Selliera radicans, Leptinella spp., Triglochin striata, Isolepis cernua, Schoenus nitens, Plagianthus divaricatus, Baumea juncea (Machaerina juncea), Coprosma propinqua, Olearia solandri, Leptospermum scoparium, Phormium tenax and Cortaderia toetoe. Also spinifex-shorebindweed sandfield with associated Pimelea arenaria (Pimelea villosa subsp. arenaria) and Desmoschoenus spiralis (Ficinia spiralis); and Juncus maritimus-Leptocarpus similis Rushland with Mimulus repens.

Environmental Requirements

P. vaginatum tolerates a wide range of environmental soil and climatic conditions, especially being highly tolerant of salinity, up to 600 mM NaCl, (35 ppt salinity) the natural level in undiluted sea water and even hyper-saline conditions (up to 50 ppt) although growth may be inhibited at these levels. Its growth is best at low salinity levels (Lonard, 2016). In Australia Barrett-Lennard et al, (2013) found the optimum salinity level for P. vaginatum to be 6-16 dS/m (seawater has 50 dS/M). Gaetani et al. (2013) also found it to grow best at about 2/3^rd the full salinity of sea water in Italy. It enjoys water-logged conditions and survives a water table at or above soil level for at least 10 months of the year. It also tolerates seasonal flooding to a depth of 50 cm or more for at least 45 days (Lonard et al., 2015). Some turf-grass varieties can tolerate drought, but Barrett-Lennard et al. (2013) found that its growth increased many-fold as the watertable depth rose from 1.3 to 0.9 m below the soil surface. It can also tolerate temporary freezing conditions.

It responds well to nitrogen up to 17.5 g/m², but is also tolerant of infertile conditions (Brosnan and Deputy, 2008).

Gaeumannomyces graminis, an ectotrophic pathogen on roots and stolons, is found in turfgrass plots in Florida and in China. This species also commonly infects wheat, rice, and other cereals. Dollar spot, Sclerotinia homoeocarpa, is the most economically important turfgrass disease in North America, while Helminosporium spp., Bipolaris spp., Drechslera spp, and Fusarium sp. have also been reported as pathogens. Basidiomycetes Rhizoctonia solani, and Waitea circinata, have been identified as pathogens of P. vaginatum in South Africa (Lonard et al., 2015). In Sri Lanka, a turf yellowing disease is caused by a Curvularia sp. (Malkanthi et al., 2014). In China, red thread caused by Laetisaria fuciformis is reported by Zhang Wu et al. (2015b); a leaf blight caused by new species, Microdochium paspali (Zhang et al., 2015a); and W. circinata by Zhang et al. (2014). Marasmiellus mesosporus has been recorded from the Dominican Republic (Miller et al., 2010).

Rice yellow mottle Sobemovirus has been identified from P. vaginatum in Nigeria (Salaudeen et al., 2008).

As many as 10 genera of parasitic nematodes have been identified associated with cultivars of P. vaginatum, the most damaging being Belonolaimus longicaudatus and Hoplolaimus galeatus. These, and Helicotylenchus pseudorobustus cause stunted root growth, decreased water and nutrient absorption, and necrotic lesions on aerial shoots. B. longicaudatus and H. galeatus populations were absent when seawater was used for irrigation (Lonard et al., 2015). Helicotylenchus, Mesocriconema and Pratylenchus species are recorded in turf grasses in Barbados (McGroary et al., 2014) and Meloidogyne marylandi in Israel (Oka et al., 2004)

Lonard et al. (2015) note that P. vaginatum is relatively resistant to many insect but report damage from the aphid Schizaphis graminum in Florida, USA, through feeding and through transmission of plant viruses. It is also relatively susceptible to army worms Spodoptera frugiperda, and to the beetle Euphoria sepulcralis. The Japanese beetle, Popillia japonica is also recorded from Florida (Braman and Raymer, 2006). The beetles Sphenophorus arizonensis and S. venatus are reported from Mexico (León-García et al., 2012; Ordaz-González et al., 2014).

Animal feed, fodder, forage

• Fodder/animal feed
• Forage

Environmental

• Amenity
• Boundary, barrier or support
• Erosion control or dune stabilization
• Land reclamation
• Landscape improvement
• Revegetation
• Soil conservation

P. vaginatum may be confused with the closely related P. distichum but the latter has more turgid spikelets, a prominent middle nerve on the lower lemma, absent in P. vaginatum, the upper glume being minutely hairy and the presence of a distinct if variable lower glume. They also differ in habitat, P. distichum rarely occurring in saline conditions. The latter is also more temperate in its distribution. The loose papery leaf sheaths of P. vaginatum may also be a helpful distinguishing feature (Graeme and Kendal, 2001).

Many other species of Paspalum can also occur as weeds. One of the most widespread of these is a complex of closely-related taxa which include P. commersonii and P. orbiculare but which are usually known as P. scrobiculatum (qv). This is widespread in Asia and Africa. It is not likely to be confused with P. distichum as it has a tufted habit whether spreading or erect; annual or perennial, but without runners or rhizomes. The inflorescence also differs in having spikelets almost round in outline.

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.

Control

Physical/mechanical control

Mechanical control alone is not really an option as it can so readily regenerate from rhizome and stolon fragments. However, cultivation, mowing and fire have all been used in conjunction with herbicide to achieve integrated control (see IPM section).

Biological control

There have been no attempts at biological control.

Chemical control

P. vaginatum is not readily controlled by herbicides. Dalapon can be relatively ineffective while glyphosate followed by burning or slashing before ploughing and puddling gave effective control before planting rice in Sierra Leone (Bernard, 1988). These treatments gave better weed control between April and June than in March. Parker (1982) reported that fluazifop-butyl and sethoxydim were superior to glyphosate in pot experiments. Brosnan and Breeden (2009), in experiments to destroy a turf-grass variety, had disappointing results from glyphosate and fluazifop-butyl but succeeded with dazomet granules. A combination of MSMA plus triclopyr plus clopyralid ‘suppressed’ P. vaginatum turf grasses but did not kill them (Johnson and Duncan, 2001). Asulam was effective against P. vaginatum but was not selective in Cynodon dactylon turf (Davis et al., 1997). Atrazine, bispyribac-sodium, and trifloxysulfuron proved too damaging for selective control of Poa annua in P. vaginatum turf but probably not damaging enough for full control (McCullough et al., 2012). Seedlings being established for turf were damaged by MSMA, imazaquin, fluazifop, triclopyr, siduron, and ethofumesate (Patton et al., 2009) but again, these may not be fully effective for control.

For control of other weeds in P. vaginatum turf, clopyralid, halosulfuron, metsulfuron, quinclorac, carfentrazone were found safe on seedlings (Patton et al., 2009). Bentazone, clopyralid, dicamba, halosulfuron, imazaquin, mecoprop+2,4-D+dicamba, metsulfuron, and quinclorac were also reported selective by Unruh et al. (2006). In Hawaii, three-way mixtures of 2,4-D, MCPP, and dicamba are labeled for use on P. vaginatum turf and provide postemergence control of many broadleaf weeds while halosulfuron and sulfosulfuron are registered for control of sedges. Sea water can also be used to control e.g. Digitaria sanguinalis and Mimosa strigillosa (Wiecko, 2003).

A turf-grass type of P. vaginatum has been developed with resistance to the herbicide glufosinate-ammonium (Kim et al., 2009).

IPM

Slashing or burning P. vaginatum followed by paraquat or glyphosate has given good control. Ploughing and puddling the first year followed by glyphosate and puddling the second year also gave effective P. vaginatum control in Sierra Leone (Bernard, 1988).

29/04/2016 Original text by:

Chris Parker, Consultant, UK