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Giant sensitive plant (Mimosa diplotricha)

Giant Sensitive Plant is an aggressive weed of Queensland’s tropical pastures and crops, particularly sugarcane. It smothers crops and pasture, and tens of thousands of hectares of Queensland tropical pastures are infested.

Key facts

Type: Weed, shrub.

Native to: Brazil.

Established in: QLD.

Other names: Creeping Sensitive Plant, Nila Grass, Tropical Blackberry.

Best time to act: In Queensland, germination is greatest at the start of the wet season in November or December, and the main flowering and fruiting period is April to the end of June.

Identification

  • It may grow as a prostrate, erect or climbing shrub, and plants can reach 2 to 3 m tall, with stems recorded up to 6 m long.
  • Its much-branched stems have 4 or 5 angles and numerous backward-curving prickles, usually 3 to 6 mm long.
  • Bright green leaves are about 10 to 20 cm long, with 4 to 9 pairs of branchlets and 12 to 30 pairs of leaflets on each branchlet; the leaflets fold when touched and at night.
  • Pink or pinkish-violet flowers grow in globular heads about 12 mm across.
  • Flat, prickly-edged pods are 10 to 35 mm long and usually split into 3 to 5 one-seeded segments.
  • Look-alike: Giant Sensitive Plant (Mimosa pigra) is a larger, upright shrub, about 6 m high, with 6 to 19 pairs of leaf branchlets and larger pods containing 14 to 26 seeds; Creeping Sensitive Plant has 4 to 9 pairs of branchlets and pods with 3 to 5 seeds.
  • Look-alike: Common Sensitive Plant (Mimosa pudica) has leaf branchlets arising from one point rather than in opposite pairs, and its leaf stalks and axes lack prickles; Coffee Bush (Leucaena leucocephala) lacks prickles and sensitive leaves and has creamy-yellow flower heads.

Where it grows

In Australia it is confined to Queensland, especially high-rainfall coastal areas of northern Queensland from Ingham to Cooktown and around Mackay, with occurrences also in wetter parts of the south-east.

Why it matters

  • It grows faster than sugarcane and its long, spiny stems smother crops, reducing yields and fouling mechanical harvesters.
  • It is unpalatable to stock and its spiny stems can form tangled thickets in pastures.
  • Animals can become trapped in thickets and die, and people can be seriously injured.
  • A form, Mimosa diplotricha var. inversa, is eaten by cattle; it may be toxic to sheep, and a report from Flores suggests the plant is toxic to pigs.

How it spreads

  • When pods break up, seeds remain in fruit segments that float on water or attach to clothing and animals.
  • Seeds can also spread in contaminated hay and other agricultural produce, soil used for building and roadwork, and unclean machinery and vehicles.

Control options

  • Cultivation, or cutting and burning mature plants, is not easily effective because plants regrow rapidly from the crown and seeds readily germinate after aerial growth is removed.
  • Where access is possible, cultivate seedlings and regularly slash mature plants to prevent them seeding.
  • The sap-sucking bug Heteropsylla spinulosa is established in Australia and has been found to reduce plant vigour and seeding; a native fungus, Corynespora cassiicola, can cause defoliation and dieback in hot, humid conditions.
  • For chemical control, consult the Australian Pesticides and Veterinary Medicines Authority for registered herbicides.

Hygiene and washdown

  • Clean machinery and vehicles, and avoid moving contaminated soil, hay or other agricultural produce, because these can carry seeds.
  • Seeds can attach to clothing and animals, and seed-bearing fruit segments can float on water.
  • Inspect and clean vehicles, plant and footwear before leaving an infested area, paying attention to tyres, radiators, belly plates, tracks and floor mats.
  • Wash down at a designated bay where runoff is contained and can be monitored for seedlings.
  • Record each washdown so the client has evidence of clean entry and exit.

Classification by state

  • Australia (national): No national listing. Managed under state and territory law.
  • Queensland: Restricted matter, category 3. Do not give it away, sell or release it into the environment. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Not a priority weed. Not a state or regional priority weed in NSW. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Declared pest (C1), prohibited. C1 Exclusion: to be kept out of WA, or out of the parts of WA where it is not established. Report any sighting to DPIRD. It must not be brought into WA (prohibited organism).
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Declared weed. Weeds Australia lists it as a declared weed in the NT under the Weeds Management Act 2001. Check the NT declared weeds list for its class and what it requires.
  • Australian Capital Territory: Not declared. Not declared under the Biosecurity Act 2023 (ACT). A general biosecurity duty still applies.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

  • Queensland: Biosecurity Act 2014 (Qld), administered by Biosecurity Queensland (13 25 23)

Sources