Alligator Weed

Family:
Amaranthaceae
Origin:
South America

General description

Emergent aquatic or terrestrial perennial herb. Stems are hollow and buoyant. Leaves are opposite, < 10 x 4 cm and waxy. Flowers are white, clover-like and borne on stalks.

What you need to know

To help protect our environment:

  • You must not breed, distribute, release or sell alligator weed. As alligator weed is a National Pest Plant Accord species, these restrictions apply within the Auckland region and across the whole of New Zealand.
  • You must not plant alligator weed within the Auckland region.
  • You must destroy any alligator weed on land that you occupy if it has been planted in breach of the above rules and you are directed to do so by an authorised person.

If you see alligator weed anywhere on Aotea/Great Barrier Island group, please report it to Auckland Council at pestfree@aucklandcouncil.govt.nz.

Still or slow-moving water bodies, pasture, cropland, gardens.

Vegetative spread from stem nodes and root fragments, dispersed by water movement. Human-mediated dispersal through movement of contaminated soil and machinery, deliberate plantings.

Alters aquatic habitat structure and invertebrate community composition, reduces native plant cover and diversity in wetlands and water body margins. Displaces valuable pasture species, blocks drainage channels and exacerbates flooding on farmland.

Site Management

Follow up treated areas 3 times per year. Encourage natural regeneration of native plants or replant treated areas where possible after 2-3 treatments to establish dense ground cover and minimise reinvasion.

Recommended approaches

Do not attempt to undertake control of this species on Aotea/Great Barrier Island group. Please report to Auckland Council if seen on Aotea/Great Barrier Island group.

Physical control

Method: Dig out or cover terrestrial sites with black plastic or weedmat for 6 to 12 months

Plant parts requiring disposal: Stems and roots

Disposal options: Compost stems and roots in a composting weed bag or remove to greenwaste or landfill

Biocontrol

Check for the presence of biocontrol agents:
  • Alligator weed flea beetle (Agasicles hygrophila)
  • Alligator weed stem borer (Arcola malloi)

Community agrichemical control recommendations

Basic Growsafe certified
For small infestations on terrestrial sites:
Foliar spray with 0.5g metsulfuron-methyl per 1L of water
For small infestations on aquatic sites:
Foliar spray with 20ml glyphosate green per 1 L of water

Certified Handler/Experienced agrichemical user
For medium to large infestations on terrestrial sites:
Foliar spray with 5g metsulfuron-methyl per 10L of water and 20ml penetrant
Foliar spray with 200ml glyphosate green per 10L of water
Foliar spray with 200ml glyphosate green per 10L of water

CAUTION: When using any herbicide or pesticide please read the label thoroughly to ensure that all instructions and safety requirements are followed.

Similar species

Senegal tea
Gymnocoronis spilanthoides

Senegal tea has serrated and wavy leaf margins. Its stems are solid as opposed to the hollow stems of alligator weed. Its flowers are clustered rather than singular.

water primrose
Ludwigia peploides ssp. montevidensis

Water primrose has alternate leaves. On its stem there are two swollen stipules at base of leaves. It has bright yellow flowers.

RPMP status


Aotea (Exclusion)
Parkland with Significant Ecological Areas (Site-led)
Whole region (Sustained Control)
National Pest Plant Accord Species
Waitākere
Alligator weed - Main species image