Stipa trichotoma, Stipa neesiana and Stipa tenuissima in the EPPO region: addition to the EPPO Alert List
Why
Stipa trichotoma (= Nassella trichotoma), Stipa neesiana (= Nassella neesiana) and Stipa tenuissima (= Nassella tenuissima) (Poaceae – common names: serrated tussock, Chilean needle grass and Mexican feather grass, respectively) are perennial grasses. All three species have been voluntary introduced into the EPPO region for ornamental purposes, where their distribution is still limited. Because these plants have shown invasive behaviour in different continents and are of limited distribution in the EPPO region, they can be considered emerging invaders in Europe.
Where
Geographical distribution of Stipa trichotoma
EPPO region: France (including Corse), Italy
Africa: South Africa
North America: USA (Illinois, Kentucky, North Carolina, South Carolina)
South America (native): Argentina, Brazil, Uruguay
Oceania: Australia (New South Wales, Tasmania, Victoria), New Zealand
Note: S. trichotoma is regulated in all Australian States and is one of the 20 weeds considered of national significance. It is estimated that it covers more than 1.1 million ha in Australia. In the USA, it is considered a noxious weed, particularly in southern states. In Corse, the species does not seem to exhibit an invasive behaviour so far.
Geographical distribution of Stipa neesiana
EPPO region: France (including Corse), Spain
North America: USA (Alabama)
South America (native): Argentina, Bolivia, Brazil, Chile, Ecuador, Uruguay
Oceania: Australia (New South Wales, Queensland, South Australia, Tasmania, Victoria), New Zealand
Note: S. neesiana is regulated in all Australian States and is one of the 20 weeds considered of national significance. Although it had been introduced in 1934 in Australia, it has only been recognized recently as a weed of major importance.
Geographical distribution of Stipa tenuissima
EPPO region: France (including Corse), Italy
Africa: South Africa
North America: USA (California, New Mexico (native), Texas (native))
South America (native): Argentina, Chile
Oceania: Australia (New South Wales, Victoria), New Zealand
Note: in Australia, S. tenuissima is regulated in Queensland, New South Wales, Southern Australia, Victoria and Western Australia.
Morphology
These three Stipa spp. are perennial grasses forming dense tussocks, their leaves are numerous, fine, bristly, tighly rolled, and rough to touch.
Stipa trichotoma
S. trichotoma has a deep fibrous root system and can live more than 20 years. It grows up to 0.6 m high and its leaves are thin, 0.5 mm wide, and glabrous. The seed is 1.5-2 mm long. The species is identifiable via the leaf bases which are more tightly packed than the other Stipa spp., slender, and whitish (never purple or blue green).
Stipa neesiana
S. neesiana can grow up to 1 m high, and leaves are 1-5 mm wide. The flowering seed heads show a distinctive purplish colour. In addition to normal flower seeds, S. neesiana produces hidden seeds at the node and bases of flower stems. The seed is 8-10 mm long and very sharp.
Stipa tenuissima
S. tenuissima grows up to 0.7 m high. Leaves are thin, 0.5 mm wide. The lower half of glumes are purplish in the lower half. The seed is 2-3 mm long.
Unlike S. trichotoma, the mature seeds of S. tenuissima do not always fully project and spread, and the flowering stem does not always break at the uppermost stem node when mature.
Biology and ecology
The three species are adapted to a wide range of climates and soils types. They are tolerant to drought, fire and grazing, but are limited by salinity and waterlogging. S. tenuissima prefers a dry temperate climate with a mean annual rainfall ranging from 300 to 800 mm. S. neesiana grows in temperate regions with annual rainfall greater than 500 mm. S. trichotoma seems to have more stringent requirements as hot summer temperatures limit its distribution. S. trichotoma does not survive repeated ploughing.
Mature plants of S. trichotoma can produce more than 140 000 seeds per plant per year which can be blown by wind over long distances (up to 20 km). S. neesiana can produce more than 20 000 seeds. Seedlings are usually out competed by other plants, but become competitive under conditions of drought or overgrazing when more favourable pasture species have already been consumed by stock.
In the state of Victoria in Australia, the area covered by S. trichotoma has been multiplied by 4 in 20 years.
In which habitats
According to the Corine Land Cover nomenclature, all three species are recorded in the following habitats: arable land, pastures, natural grassland, road and rail networks and associated land, other artificial surfaces (wastelands).
S. neessiana and S. tenuissima also invade banks of continental water, riverbanks / canalsides (dry river beds) and forests.
Pathways
All three Stipa spp. are used as ornamental plants. Seeds are spread naturally by wind or water, they adhere to clothing and livestock and can be dispersed on farm machinery or as a contaminant of seeds and fodder.
Impacts
Stipa spp. are vigorous plants which crowd out desirable pasture species, reducing stock carrying capacity. They have a high fibre content and a low nutritive value, and form indigestible balls in the stomach of stock, leading to significant losses in stock production. The sharp seeds may cause injury to stock, including blindness. As seeds contaminate wool, they can devaluate its value.
It is estimated that S. trichotoma costs New South Wales’ agriculture more than 40 million AUD annually. Additionally, in Australia, the estimated average annual cost of controlling S. neesiana is between 60 and 120 AUD per ha, depending on whether the infestation is scattered or dense.
These species also cause environmental damage to native grasslands, in New South Wales, trials on heavily infested areas by Stipa spp. can also crowd out native grasses in coastal or open areas, and create a fire hazard in urban areas.
It is predicted that S. tenuissima may be more invasive than S. trichotoma because of its ability to adapt to a wide range of climates. If left to spread, the economic cost to Australia over the next 60 years is estimated to be 39 million AUD annually.
Control
Prevention is the cheapest and most effective method. It includes avoiding purchasing hay, stock feed or stock from contaminated areas. Stock should be placed in a paddock for 7-10 days before moving them. Maintaining weed-free machinery and equipment is also very important.
All control programs should aim to reduce the amount of seed produced. Management measures include grubbing out small infestations before they flower and set seed, and to destroy them by burning. Larger infestations can be treated annually with an appropriate herbicide before plants flower and set seed. In arable lands, cultivation techniques such as ploughing may reduce the seed bank. Nevertheless, ploughing or herbicide treatment alone usually results in reinfestation of Stipa spp. from seed in the soil. Therefore an integrated management strategy should be preferred.
Continued checking and treatment is needed for 5 to 10 years to control young seedlings that germinate from the soil seed bank. Treated areas should be re-planted with desirable species.
Considering the invasive behaviour of these species in Australia, it is considered that pastures, natural grasslands and riverbanks of temperate and Mediterranean EPPO countries might be at risk.
Sources
United States Department of Agriculture Website
Delivering Alien Invasive Species Inventories for Europe
Stipa trichotoma
Australian Government (2009) Serrated tussock (Stipa trichotoma) weed management guide. 6 p.
Global Invasive Species Database (2009) Nassella neesiana.
Système d'Information et de Localisation des Espèces Natives et Envahissantes (SILENE) http://silene.cbnmed.fr/index.php?cont=accueil
Stipa neesiana
Australian Government (2009) Chilean needle grass (Nassella neesiana) weed management guide
Tela Botanica (2009) Carte des départements avec Nassella neesiana
Stipa tenuissima
Barker J, Randall R & Grive T (2006) Weeds of the future ? Threats to Australia’s grazing industry by garden plants. Meat & Livestock Australia Limited. North Sydney, NSW. 120 p.
Csurshes S (2008) Pest plant risk assessment – Mexican feather grass Nassella tenuissima. The State of Queensland, Department of Primary Industries and Fisheries. 8 p.
Global Invasive Species Database (2009) Nassella tenuissima.
Pacific Island Ecosystems at Risk (PIER) (2009) Nassella neesiana