Serious semi-aquatic weed discovered in East Kimberley

The Department of Agriculture and Food’s ongoing surveillance for priority weeds recently resulted in an additional find, with the discovery of a serious invasive weed not previously found in Western Australia.

Department priority weed response manager Kay Bailey said olive hymenachne (Hymenachne amplexicaulis), a declared plant formerly recorded only in Queensland and the Northern Territory, was discovered in the East Kimberley.

“The olive hymenachne infestation was identified by a department biosecurity officer during an aerial survey of the East Kimberley for a different weed,” Ms Bailey said.

“Steps were immediately taken by the department to determine the extent of the infestation and treat the plants, as olive hymenachne is a Weed of National Significance and prohibited in this state.

“Olive hymenachne is regarded as a serious weed due to its potential to rapidly spread from both seed and broken stem fragments.”

The semi-aquatic grass can invade wetlands, waterways, irrigation and drainage systems and low-lying commercial enterprises such as sugar cane farms.

It grows to about 2.5 metres tall and has bright green leaves with prominent, light-coloured veins, and a heart-shaped, stem-clasping leaf base.

Ms Bailey said surveillance for the weed following treatment resulted in no additional detections; however, current, wetter-than-average weather conditions were ideal for olive hymenachne to flourish.

A native hymenachne species (H. acutigluma), which has not been recorded in Western Australia, can be easily distinguished from the olive hymenachne because it does not have a heart-shaped, stem-clasping leaf base.

Following the discovery of the weed in the East Kimberley, local landholders and the community have been asked to look out for and report any unusual plants.

People who suspect they have seen olive hymenachne are encouraged to contact the department’s Pest and Disease Information Service on 1800 084 881 or email info@agric.wa.gov.au.

Alternatively, make a report using the department’s MyWeedWatcher app or online reporting tool.

Department of Agriculture and Food biosecurity officer Tracey Vinnicombe with olive hymenachne, which was recently detected and treated in the East Kimberley.

The leaf-base of the olive hymenachne plant distinguishes it from the native species.

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