Invasive pasture grasses in northern Australia - Olive hymenachne

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Olive hymenachne (Hymenachne amplexicaulis)

Hymenachne was imported into northern Queensland in the 1970s to use in ponded pastures. It escaped cultivation a few years after its release in 1988. It is spreading throughout the tropical wetlands of northern Australia and is most common in the coastal wetlands of northern Queensland and the Northern Territory. Olive hymenachne also grows in northern New South Wales. It has not established in Western Australia, although the Kimberley region is at high risk of invasion.

Olive hymenachne under state and territory legislation

Olive hymenachne (Hymenachne amplexicaulis) is a Weed of National Significance and it is also a declared weed throughout Australia.

Under Western Australia’s Biosecurity and Agriculture Management Act 2007 it is prohibited under section 12. It has been placed in the C1 control category (exclusion – not established in Western Australia and control measures are to be taken, including border checks, to prevent them entering and establishing in the state).

Under the Northern Territory’s Weeds Management Act 2001, olive hymenachne is classified as a Class B/C weed (further introductions of the species into the Northern Territory are prohibited and land managers must control its growth and prevent spread).

Under Queensland’s Land Protection (Pest and Stock Route Management) Act 2002, olive hymenachne is a declared Class 2 pest (land managers must take reasonable steps to keep land free of the species and it is an offence to introduce, keep or supply the species without a permit).

Under New South Wales’ Noxious Weeds Act 1993, olive hymenachne is declared a Class 1 weed state wide (it must be eradicated from the land and the land must be kept free of the plant).

Under the Australian Capital Territory’s Pest Plants and Animals Act 2005, olive hymenachne is a prohibited pest plant (propagation and supply is prohibited).

Under Victoria’s Catchment and Land Protection Act 1994, olive hymenachne is classified as a restricted weed state-wide – it has or may have the potential to become a serious threat to primary production, Crown land, the environment or community health in Victoria or in another State or a Territory of the Commonwealth. It cannot be sold or traded as it poses an unacceptable risk of spread.

Under South Australia’s Natural Resources Management Act 2004 olive hymenachne is a declared weed. A person must not sell it or sell anything that carries it (i.e. contaminated by it).

Under Tasmania’s Weed Management Act 1999 olive hymenachne is a declared weed (importation, sale and distribution are prohibited).

Priority actions/research (recent or underway)

Olive hymenachne is a Weed of National Significance (WoNS) under state and territory management. The 2012 review of the Hymenachne National Strategic Plan lists the following key achievements for hymenachne management since its declaration as a WoNS in 1999:

• Guideline for the containment of olive hymenachne (Hymenachne amplexicaulis) to genuine grazing systems. AgForce Queensland and the Northern Territory Cattleman’s Association endorsed this document in 2011.
• Extension and awareness activities and materials such as attendance of field days and conducting forums, preparation and delivery of resource kits, signage for recreational waterholes, banners for field days, television and newspaper coverage.
• In June 2001 the Queensland Government released its ‘Policy for development and use of ponded pastures’, recommending against the use of hymenachne and para grass.
• Hymenachne control methods and case studies manual (2006) includes:
  • a comprehensive range of control and management tools for combating hymenachne
  • case studies demonstrating landholder approaches and experiences.

Managing threats to floodplain biodiversity and Indigenous values (Setterfield S, Douglas M, Bayliss P, Jackson S, National Environmental Research Program (NERP) North Australia Hub, 2014). The NERP North Australia Hub continues to work with Northern Territory and Queensland government agencies to improve our understanding of the distribution, impacts and management of the five grasses. This project aims to improve the understanding of the spread of para grass and olive hymenachne in the tropical floodplains, and how spread patterns are related to hydrological regime, fire, and edaphic factors. The project will deliver maps of distribution of these weeds in Kakadu, models of areas of habitat suitable for invasion and predicted patterns of spread. It will also develop an improved decision-support tool to guide the implementation of cost-effective strategies to control aquatic invasive grasses.

Resources