Paspalum dilatatum
(dallisgrass)

Paspalum dilatatum is a perennial grass native to South America that has been introduced into tropical and subtropical areas as a forage species/fodder. It is reported as invasive in Japan, Malaysia, Taiwan, Vietnam, Indonesia, Philippines, Hawaii, American Samoa, Australia, Fiji, French Polynesia, New Caledonia, New Zealand, Niue, Norfolk Island, Solomon Islands and the Minor Outlying Islands. In Hawaii and New Zealand, it forms dense stands that smother and prevent recruitment of native species.

P. dilatatum is native to Brazil, Argentina, Bolivia, Chile, Guyana, Paraguay and Uruguay (Missouri Botanical Garden, 2017; PIER, 2017; PROTA, 2017; USDA-ARS, 2017), and Hanelt (2017) extends its reported native distribution to Central America. The species has been introduced worldwide, being present in Asia, Africa, North America, Central America, the Caribbean, South America, Europe and Oceania and invasive in many of the introduced countries (Acevedo-Rodríguez and Strong, 2012; DAISIE, 2017; Encyclopedia of Life, 2017; Missouri Botanical Garden, 2017; PIER, 2017; PROTA, 2017; USDA-ARS, 2017).

P. dilatatum has a medium to high risk of introduction into tropical, subtropical and temperate zones, usually to be used as forage/fodder. However, its low sexual reproduction, low germination and slow establishment, together with its susceptibility of being infected by ergot (Claviceps paspali), are a deterrent to its spread. Nevertheless, the use of this species is favoured due to the high productivity of livestock that feeds on it (Miz and Souza-Chies, 2006). As research to identify genotypes that improve its use as a crop is underway, its distribution is likely to increase in the future (Glison et al., 2015).

P. dilatatum is present in disturbed sites, savannas, moist grasslands, forests, wetlands, riparian habitats, roadsides and agricultural land (Flora do Brasil, 2017; PIER, 2017). It grows from 5 to 2200 m of elevation (PROTA, 2017).

P. dilatatum is reported as a weed of cultivation and is sometimes present in rice fields (Heuzé et al., 2015; Flora of China Editorial Committee, 2017). When the species is infected by the ergot fungus, Claviceps paspali, it becomes toxic to animals that feed on it (FAO, 2017; PROTA, 2017; USDA-ARS, 2017).

Genetics

The chromosome numbers reported for P. dilatatum are 2n = 40, 50, 60 (PROTA, 2017). Germplasm collections are stored at various institutions, with the oldest collection in storage being around 21 years old (Glison et al., 2015; Kew Royal Botanic Gardens, 2017; PROTA, 2017; USDA-ARS, 2017). DNA barcode information for the species is available at the Barcode of Life Data Systems (BOLD, 2017). Seeds are produced in Australia, USA and Uruguay, and breeding work is being undertaken to increase species resistance to ergot and anthracnose, and to improve species management (Glison et al., 2015; PROTA, 2017).

The species is mainly apomictic by apospory and pseudogamy, with the sexual type being less common. Crossing apomict and sexual plants produces an interspecific hybrid with 2n = 50 (PROTA, 2017). There are reports of hybrids between P. dilatatum and P. urvellei (Miz and Souza-Chies, 2006). Important cultivars developed for P. dilatatum are ‘raki’ from New Zealand, ‘charu’ from Uruguay and ‘natsugumo’ from Japan (PROTA, 2017).

Reproductive Biology

Reproduction of P. dilatatum is by seed (PROTA, 2017). Most seeds are produced by apomixis, although wind pollination and pollination by solitary bees have been reported for the species (Adams et al., 1981). Pollen viability is low (Miz and Souza-Chies, 2006). Seed production is 570-750 seeds/g and is inhibited below 13°C (FAO, 2017; PROTA, 2017). Seeds have some post-harvesting dormancy, which is broken by removal of the glumes (FAO, 2017; PROSEA, 2017). It is considered a slow starter species, with slow germination and establishment rates (Miz and Souza-Chies, 2006; PROTA, 2017).  

Physiology and Phenology

P. dilatatum flowering and fruiting occurs from spring to summer, after which flowering declines (FAO, 2017; Flora of China Editorial Committee, 2017). Early growth is slow but, once established, it grows vigorously. The fastest growth occurs during the reproductive season and slows down during mid-summer and autumn. In subtropical regions and at higher altitudes, the species becomes dormant during cool periods (PROTA, 2017).

Associations

P. dilatatum is usually grown with other fast growing plants in order to improve pastures (Heuzé et al., 2015). Species that are grown in association with P. dilatatum are Trifolium repens, T. semipilosum, T. subterraneum, Vigna parkeri, Cynodon dactylon and Lolium rigidum (Heuzé et al., 2015; PROTA, 2017).

Environmental Requirements

P. dilatatum can grow in areas with annual rainfall from 750 to 1650 mm, but is better adapted to permanently humid subtropical conditions of 10 to 12 humid months, with over 1000 mm annual rainfall (FAO, 2017; PROTA, 2017). It prefers moist fertile soils of fine and medium texture, with a pH of 4.9 to 7.5, although it can grow on heavy clay soils (Encyclopedia of Life, 2017; FAO, 2017). The species tolerates flooding, but will also grow in dry areas, being drought tolerant (Heuzé et al., 2015; PROTA, 2017). It is not common in areas exposed to fires, although it recovers well from them (FAO, 2017). Optimum growing temperature is 22 to 30°C, but it can grow in temperatures as low as -3°C, as its deep roots allow it to regrow after frost (Heuzé et al., 2015). It requires full sun and has an optimal day-length response of 14-16 hours (PROTA, 2017).

P. dilatatum is affected by the following pests: Claviceps paspali, Glomerella graminicola [Colletotrichum graminicola] and Helminthosporium micropus [Bipolaris micropus]; the insects Lepidiota caudata, Rhopaea spp. and Diatraea saccharalis; and the barley and cereal yellow dwarf viruses (B/CYDV) and the Paspalum striate mosaic virus (PSMV) (Geering et al., 2012; Rúa et al., 2014; FAO, 2017; PROTA, 2017).

Animal feed, fodder, forage

• Fodder/animal feed
• Forage

Environmental

• Erosion control or dune stabilization
• Soil conservation

P. dilatatum is similar to P. mandiocanum, P. notatum, P. urvillei, P. scrobiculatum and P. quadrifarium (University of Queensland, 2017). These species can be differentiated by the following: P. dilatatum is a moderately-sized grass with narrow leaves, large flower spikelets (3-4 mm long), long silky hairs on the leaf margins and seed-heads usually with 3-7 branches. P. mandiocanum is a low-growing grass with broad leaves, small flower spikelets (2-2.5 mm long), without long silky hairs on the leaf margins and seed-heads usually with 3-10 branches. P. notatum is a low-growing grass with relatively narrow leaves, relatively large flower spikelets (2.75-4 mm long), without silky hairs on the leaf margins and seed-heads usually with only two branches. P. urvillei is a tall grass with narrow leaves, small flower spikelets with long silky hairs on the leaf margins and seed-heads usually with 10-20 branches. P. scrobiculatum is a moderate-sized grass with narrow leaves, small flower spikelets (2-2.5 mm long), without long silky hairs on the leaf margins and seed-heads usually with only 2-7 branches (i.e. racemes). P. quadrifarium is a tall grass (1-2 m tall) with narrow leaves, relatively small flower spikelets (2-3 mm long), without long silky hairs on the leaf margins and seed-heads usually with 15-25 branches.

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.

Prevention

In Canada, although the species is not present, it is listed as a prohibited noxious weed under the Seeds Act (Canadian Food Inspection Agency, 2017).

Control

Physical/mechanical control

Small plants of P. dilatatum can be dug out, removing all rhizomes. Plants that are cut or mowed regenerate fast, so mowing should be combined with chemical control (Henry et al., 2007a; PIER, 2017).

Chemical control

Herbicides recommended for the control of P. dilatatum are: paraquat, glyphosate, thiencarbazone-methyl, foramsulfuron, halosulfuron-methyl, fluazifop and monosodium methanearsonate (MSMA) combined with foramsulfuron (Henry et al., 2007b; Elmore et al., 2013; Johnston and Henry, 2016; PIER, 2017).

More detailed information about the species impacts on habitats and other species is needed.

07/02/17 Original text by:

Jeanine Vélez-Gavilán, Department of Biology, University of Puerto Rico, Mayaguez, Puerto Rico, USA