Macrophyte of the Month – Juncus acutus

Spiny rush
WEED PROFILE

There are lots of local native Juncus species that are excellent plants for vegetated WSUD assets.  Juncus acutus is not one of them.

uncus acutus, Spiny rush, is a declared weed in South Australia under the Landscape South Australia Act 2019 which means that land managers must control it, and it cannot be planted or transported. It is an excellent example of why landscape architects and other professionals who specify plants for WSUD and other green spaces need to know their onions, or Juncus species in this case.

Juncus acutus would be great for WSUD due to its extreme hardiness, except that its hardiness is what makes it such a problematic weed.

It is native to Europe, Africa and North America with the following characteristics:

• Perennial plant forming large tussocks, outcompeting other more desirable plants
• Invades wetlands, watercourses and pasture, as it is able to colonise pastures following rain, even if there is no standing water
• Unpalatable and therefore not eaten by stock or other herbivores, allowing it to proliferate unabated
• Obstructs water movement, has moderate to poor stormwater treatment capacity and increases flood risk
• Hinders movement of animals in wetland environments and does not provide suitable shade and shelter for wetland fauna due to its spiky character.

How to identify Juncus acutus (Spiny rush):
Tussock forming rush up to 1.6m high. Very spikey ends of spines that will sting your hand if touched – note it can pierce skin.

Flowers throughout the year on culms (stems) that are 2-4mm wide. Flower inflorescences are 4-13cm long and have 1-6 flowers.

Fruits are ovoid, 3-celled brown capsule with seeds 1.2-2mm long and brown in colour. Characteristic global shape of tussocks makes it is easy to spot at a distance, with sharp spines projecting at many angles.

If left uncontrolled, this plant will form impenetrable thickets with low habitat value that will displace most other plants, especially pasture grasses.

Tips for good hygiene practices:

1. Avoid working in infested areas unless controlling the weed to avoid spreading the plant
2. Undertake control works prior to seed set
3. Do not remove seeds or plants from infested areas
4. Decontaminate stock and clothing/boots before leaving infested area
5. Do not move contaminated mulch or sediment from infested areas
6. Brush down all equipment, machinery and vehicles when leaving infested areas.

Control methods:

• Focus on eradicating small infestations by destroying root system and preventing seed dispersal, then act on larger infestations
• Use a combination of methods e.g. hand grub smaller plants and areas of infestation, or plough up larger infestations – making sure to remove all rhizomes from which plants can resprout
• Only spray with approved herbicides when actively growing and thoroughly wet all foliage. Remove foliage that dies off and re-spray green growth – refer to chemical control handbooks from PIRSA or relevant Landscape Boards.

Peer Review and  Biosecurity Check Service