Hymenachne is a semi-aquatic perennial grass that forms dense infestations in freshwater systems. It has become a major weed of northern Australia where it was originally introduced (to Queensland and the Northern Territory) as fodder for cattle in ponded pasture systems. It has since escaped cultivation and become an unwanted pest of wetlands, flood plains, irrigation systems, water storage facilities and sugar cane crops.
Hymenachne infestations displace native plants, reduce biodiversity and threate native fish populations and wetland habitats.
Native hymenachne (H. acutigluma) is a tropical species that grows in northern Australia and is not considered a problem.
Native to the tropics of South and Central America, hymenachne has been used as a source of dry season fodder for cattle in Venezuela, Mexico and Cuba. It is considered a serious weed in Indonesia, Suriname, Trinidad and the Florida wetlands of USA.
Many infestations occur throughout northern and central Queensland and the Northern Territory, including conservation areas of Kakadu National Park.
In New South Wales (NSW) small, isolated infestations have been found in various locations in the Richmond, Tweed and Clarence River catchments on the North Coast. All known infestations are subject to control programs, with the aim of eradication.
If left undetected, hymenachne has the potential to spread further in northern NSW and become a major weed of wetlands and waterways.
Hymenachne reproduces by seed and broken stem fragments.
Each flower head can produce over 4000 viable seeds, generally in the autumn months as day length decreases. On land, seeds require contact with waterlogged or moist soil for at least 48 hours before germinating. Germination can occur at any time of the year but more commonly from November to March. Seeds can survive in water and are spread during annual flooding events and in mud attached to the fur or hooves of animals. Waterbirds may also be responsible for spreading seed.
Broken stem fragments can be carried to new locations by floodwaters, and then take root in moist soil.
Hymenachne is a perennial grass that prefers swampy or seasonally flooded areas, growing in water up to 2 m deep.
Key identification features
Hymenachne will invade freshwater wetlands, flood plains and stream banks. Hymenachne thrives in nutrient-rich water.
2006 edition prepared by Rachele Osmond; 2013 edition reviewed by Rod Ensbey and edited by Elissa van Oosterhout.
Charleston K (2006) Hymenachne (Hymenachne amplexicaulis) Control methods and case studies, Queensland Department of Natural Resources, Mines and Water
Hosking JR, Sainty GR, Jacobs SWL & Dellow LL (in prep) The Australian WeedBOOK.
Hymenachne is difficult to control and is capable of spreading from plant fragments, requiring strict hygiene procedures during its removal. If you suspect you have found hymenachne, immediately contact a local council weeds officer who will assist with identification, removal and eradication.
See Using herbicides for more information.
PERMIT 13921 Expires 30/06/2017
Glyphosate 360 g/L (Only products registered for aquatic use)
Rate: 14 L / hectare
Comments: Apply by boom, handgun or knapsack, a maximum of 4 times a year. Refer to permit for further comments.
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate
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State Prohibited Weed
The plant must be eradicated from the land and that land must be kept free of the plant