Hymenachne

• Robust, rhizomatous, perennial grass, up to 2.5m tall.
• Stems are erect and pithy.
• Leaf blades are 10–45cm long, up to 3cm wide.
• Flower heads are spike-like, cylindrical, 20–40cm long.

• Prefers streambanks, shallow wetlands and irrigation ditches.

• Visit Weeds Australia and click on the distribution tab to access the distribution map.

• Flowering occurs April–June.
• Seeds set from late autumn to early spring.
• One flower stalk can produce more than 4000 seeds.
• Seed viability is 8–24% after 8 years.

Environmental

• Affects drains, lagoons, wetlands, creeks and rivers.
• Increases flooding by reducing flow capacity of drainage networks.
• Interferes with wildlife habitats.

Economic

• Interferes with irrigation and infrastructure.

Social

• Degrades water quality for recreational purposes.

• Seeds spread by water movement and migratory aquatic birds.

• Find out how farmers can prevent weed spread.
• Find out how gardeners and outdoor enthusiasts can prevent weed spread.

Physical/mechanical control

• Mechanical or physical removal will not completely eradicate hymenachne because of the plant's ability to reproduce vegetatively from very small pieces.
• Heavy earth-moving machinery can be effective.
• Fire is a tool for the dry season. When integrated with other control methods, fire can improve overall results and reduce cost.

Herbicide control

• No herbicides are currently registered. However, off-label minor use permits are available.
• Spraying an entire heavy infestation can cause hymenachne to sink and result in biological hazards from rotting vegetation. Large masses of decomposing hymenachne may use all oxygen in water, leading to fish kills. Avoid this problem by spraying strips of weed.

Read the Hymenachne fact sheet (PDF, 1.1MB) for herbicide control and application rates.

Biological control

• No biological control agents released in Queensland.
• Should a biological program commence, agents sought would need to be specific for olive hymenachne to ensure no impacts on native species (H. acutigluma) or other desirable grasses.

• Hymenachne is a category 3 restricted invasive plant under the Biosecurity Act 2014.
• It must not be given away, sold, or released into the environment. Penalties may apply.
• You must take all reasonable and practical measures to minimise the biosecurity risks associated with dealing with Hymenachne under your control. This is called a general biosecurity obligation (GBO).
• At a local level, each local government agency must have a biosecurity plan that covers invasive plants in its area. This plan may include actions to be taken on Hymenachne. Some of these actions may be required under local laws. Contact your local council for more information.