Alligator weed

• This vigorous perennial weed grows both in water and on land.
• Stems are hollow.
• Leaves are dark green with a distinct midrib, 2–12cm long, 0.5–4cm wide, and arranged in opposite pairs along the stem.
• There is no leaf stalk.
• Flowers are white, paper-like and ball-shaped. They are on short stalks 2–7cm long.

3D Model

• View the 3D model to help you identify this plant. You can magnify the image and manipulate the view to inspect the plant from every angle.

• Optimum growth occurs in fresh water with a high nutrient level.
• Can tolerate brackish water.
• Can establish in semi-aquatic areas, in wetlands, on stream and creek banks, and on land.

• Visit Weeds Australia to view a distribution map (select the distribution tab).

• Forms new shoots in spring from nodes on existing stems.
• Does not produce viable seed.
• Regrows quickly from stems or underground rhizomes.
• Flowers around midsummer.

Environmental

• Poses an extreme threat to waterways and wetlands.
• Restricts water flow in creeks, channels and drains.
• Reduces water quality.
• Reduces water bird and fish activity.
• Kills fish and submerged native water plants.
• Replaces native wetland plants.

Economic

• Damages pumps and irrigation equipment.
• Poses an extreme threat to irrigated croplands.
• Increases water loss through evapotranspiration.

Social

• Impedes water sports and boating access.
• Endangers swimmers.
• Creates favourable habitat for mosquitoes.

• In water, stems break and float away to form new mats.
• Cuttings in soil or on equipment are spread when these are moved.

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

Mechanical control

• Successful mechanical removal of alligator weed is extremely difficult because the plant can re-establish from very small pieces.
• If care is not taken during mechanical control, spread is likely to occur by 2 methods:
  • re-establishment from stem fragments
  • spillage in transit or at dump sites.

Herbicide control

Biological control

Three biological control agents from South America have been introduced into New South Wales. Two of these insects are established and contribute to control of alligator weed growing in water but not on land:

• flea beetle (Agasicles hygrophila)
• stem-boring moth (Arcola malloi).

• Alligator weed is a category 3 restricted invasive plant under the Biosecurity Act 2014. You must not:
  • give it away
  • sell it
  • release it into the environment.
• You must take all reasonable and practical measures that are under your control to minimise the biosecurity risks associated with dealing with alligator weed. This is part of your general biosecurity obligation.
• 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 alligator weed. Some of these actions may be required under local laws. Contact your local government for more information.