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Mexican feathergrass

Mexican feather grass is a drought resistant perennial (lives on year to year tussock (grouped) grass considered a potential threat to pasture production, native grassland, grassy woodlands and the associated fauna in the SA metropolitan area.

Description

Mexican feather grass is a long-lived, tufted, upright grass, while lower leaves may lay flat to the ground. In winter, tussocks can appear white in colour. Linear leaves are very slender (less than 1 mm wide), bristly, tightly rolled and rough to touch. The round flowering stems can reach 1 m in height but usually grow to 70 cm tall and have 2 - 3 joints, are smooth and hairless, with the lower section encased in a sheath (protective covering).

The seed head is generally open, slender and branched, 10–30 cm long, which can appear green or purplish when in flower in summer. Mature seed heads do not always fully emerge from the stem. Seeds are 2-3 mm long with a ring of tiny hairs where the 45–90 mm awn (tail of the seed) attaches. Seed production is very high and seed can remain viable for 4 years in the soil.

Similar species

Mexican feather grass is one of 3 declared weedy Nassellas known to be present in the Green Adelaide region. They are all tussock forming grasses, similar in growth habit but with subtle differences in how the seed looks. Chilean needlegrass (Nassella neesiana) is found around One Tree Hill and Texas needlegrass (Nassella leucotricha) around the Clarendon area.

Mexican feather grass and other Nassellas can be easily mistaken for many native tussock-forming grasses such as Poa (seeds do not have awns) and spear grasses (Stipa species), so the identity of an infestation needs to be confirmed before a control program is begun.

Mexican feather grass was introduced as an ornamental garden plant. Photo Monica Seiler

Impacts

In the SA metropolitan area, Mexican feather grass may encroach idle pastures and dryland reserves from roadsides, and populate parks, amenity areas and industrial sites.

Due to its likeness to many native tussock grasses, Mexican feather grass can grow unnoticed in native vegetation and potentially displace native grasses and other herbs impacting on native grasslands and grassy woodlands and associated fauna habitat.

Mexican feather grass is unpalatable to stock. Grazing selection can reduce productivity of palatable pasture leaving a monoculture of and a build-up of dry Mexican feather grass, increasing fire risk intensity.

The native, Poa labillardierei (common tussock grass) is also widely used in landscaping. Photo: Monica Seiler

Distribution

Mexican feather grass is native to central and South America, and was introduced under an incorrect name as a garden ornamental in the 1990’s. It was planted in gardens in Adelaide, on the Fleurieu Peninsula and in Mount Gambier. It is considered a potential weed of semi-arid (rainfall of around 250-500mm) and temperate (moderate rainfall) regions, which includes the Green Adelaide region.

Although plants from the initial introduction to South Australia have mostly been eradicated, some plants are still being found in gardens in Adelaide and southern rural townships.

Mexican feather grass is drought resistant and grows on a range of well-draining soils and readily reproduces in garden beds. Propagation of seedlings and sharing with friends is the most common way plants are further spread.

The small seeds are mostly spread by wind or attached to animals or clothing, machinery, vehicles or as a contaminant in fodder and soil. The long awns of the seed often entwine forming rounded clusters that move by the wind like tumbleweed.

Control

Mexican feather grass is a State Alert Weed and declared under the Landscape South Australia Act 2019. The sale of Mexican feather grass or contaminated goods; and its movement into new areas or on a public road are prohibited. It is the responsibility of the land owner to destroy these plants on their property. Sightings of this weed must be reported to Green Adelaide. Green Adelaide encourages the destruction of all plants and is keen to assist landholders with the appropriate removal of any identified plants.

Seed heads are fine with mature seed a purple colour Photo: Monica Seiler

Control methods

Hygiene

To prevent the spread of Mexican feather grass, thoroughly clean clothing or garden tools of any attached seed before leaving an infested area.
Do not move contaminated soil.

Mechanical

Grubbing or digging out of plants is effective for small isolated populations and in sensitive areas of native vegetation. Removed plants should be placed in thick, heavy duty garbage bags, double bagged and securely sealed. These can be placed in household rubbish bins.
Soil disturbance should be minimised to avoid stimulating any Mexican feather grass seeds from germinating that may be left in the soil. Covering the sites with a thick layer of mulch may also help suppress these seed from germinating. Monitor sites for several years and destroy any new seedlings before seed development.

Chemical

During active growth, foliar herbicides (weedkillers) can be used on individual plants, in pastures or on roadsides and disturbed sites. This method is most effective when combined with pre-mowing and then spraying of regrowth. Avoid contact with desirable plants.
For advice on chemical options please refer to Controlling declared weeds in SA at: www.pir.sa.gov.au/biosecurity/weeds