Pennisetum setaceum
(fountain grass)

Pennisetum setaceum, commonly known as fountain grass, is a popular ornamental plant and has been planted widely in areas with warm, arid climates. It has spread by seed into natural areas from cultivated plants. Fountain grass has become invasive in Hawaii and the southern continental United States, Australia, the Canary Islands, southern Europe, and southern Africa. It establishes monocultures in many different habitats, but is particularly problematic in dry grasslands and early successional habitats. It increases fire frequency and the ability of fires to spread within a landscape and threatens rare plant species (Benton, 2009).

Fountain grass is listed as a category one invasive species in South Africa (PlantZAfrica, 2012). It is regulated as a noxious weed in the USA in Hawaii (USDA-NRCS, 2012) and Nevada (Nevada Department of Agriculture, 2012; Weed Center, 2012) and is on the noxious weed watch list in New Mexico (Weed Center, 2012). It is also listed as a noxious weed in New Zealand (HEAR, 2012) and in Australia in New South Wales and Queensland (Weeds Australia Database, 2012).

P. setaceum is widely distributed in warm, arid climates. It is widespread on the Hawaiian islands (found on Kauai, Lanai, Oahu, Kahoolawe, East Maui, Hawaii islands). In the continental United States it grows in Oregon, California, Arizona, New Mexico and Colorado as well as in Louisiana, Florida, and Tennessee (Wunderlin and Hansen, 2008; University of Tennessee, 2012; Jepson Flora Project, 2012; GBIF, 2012). The species is widespread in southern and central California and in Arizona. It grows throughout southern California and in the Sacramento Valley, central coast, and San Francisco Bay area (Jepson Flora Project, 2012). In Arizona it occurs in most of the southern counties. It is described as naturalized and escaped from cultivation in Broward, Miami-Dade and Palm Beach counties in Florida. It grows in three counties in Tennessee (University of Tennessee, 2012).

Australia also lists it in several regions. It is most widespread in Queensland, New South Wales and Western Australia, but it also occurs in Victoria, South Australia, and in arid areas of the Northern Territories. New Zealand collections of fountain grass show that it occurs in several important ecological regions in the country (GBIF, 2012).

Fountain grass was introduced to southern Africa from North Africa and is considered invasive in Namibia and South Africa (Joubert and Cunningham, 2002).

In Europe, it has naturalized in southern countries and is recorded as an invasive species in Sicily (Pasta et al., 2010).

The main pathway for introduction of P. setaceum is through the horticultural trade. Plants and seeds are available at nurseries and by mail order. Seeds are easily dispersed by wind, water, animals and vehicles. Spread is often along roads and rivers (Rahlao et al., 2010a). It is most widespread in Hawaii and arid parts of Australia.

Fountain grass is listed as a category one invasive species in South Africa (PlantZAfrica, 2012) and is regulated as a noxious weed in the USA (Weed Center, 2012). It is also listed as a noxious weed in New Zealand (HEAR, 2012; EPPO, 2012) and in Australia in New South Wales and Queensland (Weeds Australia Database, 2012).

P. setaceum generally favours arid to semi-arid environments but occurs in mesic sites as well. It is outcompeted by other plants in wetter sites (EPPO, 2012). It often grows in disturbed areas such as along roadsides and railroad embankments and in mined areas (FloraBase, 2012). In natural areas in the southwestern USA and northern Mexico it has been found growing in grasslands, desert, desert shrublands, canyons, and rocky hillsides, coastal dunes, coastal sage scrub, and canyons. In Hawaii it grows on lava flows and rangeland at a wide range of elevations from sea level to 2900 m. In South Africa it is found in coastal vegetation, woodlands and grasslands (Rahlao et al. 2009; FloraBase, 2012).

Genetics

Poulin et al. (2005) found that there is no genetic variation among populations in the USA, as would be expected if the plants were completely apomictic (they form seeds asexually). P. setaceum is a triploid whereas P. advena is a hexaploid that may be pollen-sterile (Halvorson and Guertin 2003). Plants have high phenotypic plasticity allowing them to establish in a wide range of habitats (Le Roux et al., 2007).

Reproductive Biology

Plants begin to produce seeds within one year of seed germination (EPPO, 2012). P. setaceum mainly reproduces by self-pollination but occasionally produces seeds through cross-pollination; Halvorson and Guertin (2003) cite two studies that found some sexual reproduction in P. setaceum, however most seeds are produced through apomixis. Wind and gravity move pollen within the plant and between plants (Halvorson and Guertin 2003). Seed production is sometimes reported as very low (1.7-5.7% per plant or an average of 62 viable seeds per plant) (Goergen and Daehler, 2001), but others report that 80% of seeds produced are viable (Nonner, 2005; WeedBusters, 2012) and Poulin et al. (2007) counted an average of 100 seeds per plant in a greenhouse study. Milton et al. (2008) reported a case of pseudo-vivipary from flooded plants in South Africa where seeds produced young plants before dispersing. Seeds can remain viable for six years in soil (Halvorson and Guertin, 2003). They do not need light to germinate and can germinate when covered lightly with soil (Nonner, 2005).

Physiology and Phenology

P. setaceum is a C4 perennial bunchgrass that can live up to 20 years (Encycloweedia, 2012). Plants begin to produce seeds within one year (EPPO, 2012). Seeds germinate late spring to early summer. Seedlings require some moisture to establish (Rahlao et al., 2010b). Plants can flower over a long time period from spring to late fall before they go dormant in winter in temperate environments.

P. setaceum allocates much of its biomass to roots and shoots allowing it to be a good colonizer. It has high photosynthetic rates that also enable it to compete effectively. It also shows phenotypic plasticity in growth allocation and photosynthetic rates potentially allowing it to colonize a wider range of habitats (Williams et al., 1995; Le Roux et al., 2007; Poulin et al., 2007).

Associations

In Hawaii, more than 75% of the roots of P. setaceum were associated with vesicular-arbuscular mycorrhizae (Koske et al., 1992). Mycorrhizae help plants obtain nutrients.

Environmental Requirements

P. setaceum prefers regions with mild winters and summers with some moisture. Fountain grass prefers open sunny areas with well-drained soils, but will grow in soil types from clay to sand and can persist in light shade. It grows best in regions with median rainfall of less than 127 mm/year (EPPO, 2012) but can be found in areas with more than 600 mm rainfall/year (Joubert and Cunningham, 2002). This species cannot tolerate freezing temperatures.

Natural enemies have not been studied for this species because several related species are economically important (Markin et al., 1992). Few insect or fungi species were found to attack fountain grass in Hawaii (Goergen and Daehler, 2001).

Environmental

• Amenity
• Erosion control or dune stabilization
• Land reclamation
• Landscape improvement
• Soil conservation

General

• Botanical garden/zoo

Ornamental

• Propagation material
• Seed trade

Cenchrus advena, (Wipff and Veldkamp) Morrone, synonymous with Pennisetum advena and Pennisetum setaceum var. rubrum, is most similar in appearance and most closely related. This is a new name given to the variety with 54 chromosomes and red coloration in the leaves and inflorescenses (Wippf and Veldkamp, 1999). The origin of this species is unknown. P. advena rarely produces viable seeds. Its morphology is slightly different to P.setaceum as it has wider leaf blades without a thickened mid-vein, it usually has secondary branching at aerial culm nodes, and the inflorescence has 10-17 fascicles/cm mid-inflorescence, the inner bristle of the fascicle has 4-10 ciliate or plumose bristles, and the lower floret is staminate (Q-Bank, 2012). Whereas, P. setaceum has 8-10 fascicles/cm, the inner bristle of the fascicle has 8-16 ciliate bristles, and the lower floret is usually sterile, although sometimes staminate (Q-Bank, 2012).

P. setaceum is also similar in appearance to Muhlenbergia emersleyi, native to the Sonoran desert region in the United States. M. emersleyi grows to approximately 1m and has flattened, nodding seed heads as opposed to cylindrical seed heads. Cenchrus ciliaris, buffelgrass, is a smaller grass with branched stems and shorter cylindrical seed heads (Arizona -Sonora Desert Museum, 2012). Pennisetum villosum is also similar in appearance but has shorter, white seed heads and rhizomatous growth (Jepson Flora Project, 2012).

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          

The European and Mediterranean Plant Protection Organization evaluated P. setaceum and listed it as a priority for action (Brunel et al., 2010). Fountain grass is also on a watch list for New Mexico and listed as a noxious weed in Nevada where it occurs infrequently still (Weed Center, 2012).

In Hawaii at the Pohakuloa Training Area, researchers studying control techniques for P. setaceum invited school groups, hosted teacher workshops, and led public tours on Earth Day to increase public awareness about fountain grass (Evans et al., 2005).

Containment/Zoning

Road and river interchanges, also associated with disturbances away from roads (Rahlao et al. 2010a). Questad et al. (2012) found that native species diversity declined more in lower resource habitats and recommend focusing on these habitats in addition to high diversity habitats.

Control

Physical/Mechanical Control

Seedlings are easily pulled out by hand and larger plants can be dug out using a pick or shovel. It is important to bag or otherwise destroy the seed heads to prevent further seed dispersal (Halvorson and Guertin, 2003). Skin irritation can occur from the leaves and seed heads so gloves should be worn (Queensland Government, 2012). 

Biological Control

No biological control agents are currently being investigated.

Chemical Control                                 

Herbicides containing fluazifop, quizalofop, sethoxydim, fenoxaprop, hexazinone, and glyphosate have been used to control fountain grass (FloraBase, 2012; Halvorson and Guertin, 2003). Some herbicides should not be used near waterways or trees. 

Ecosystem Restoration

A study in Hawaii tested several techniques for re-establishing native vegetation (Cabin et al. 2002). Both reducing the abundance of P. setaceum and planting native species helped speed ecosystem restoration. Decreasing nitrogen levels may also favor native grasses (Carino and Daehler, 2002).

20/08/12 Original text by:

Sylvan Kaufman, Denton, Maryland, USA