Alligator weed found in Tauranga wetland

Bay of Plenty Regional Council and Tauranga City Council staff are working together to remove and control an infestation of the aggressive aquatic pest plant alligator weed from a Tauranga wetland.

Alligator weed (Alternanthera philoxeroides), which also grows on land, was discovered by a regional council biosecurity officer during a routine pest plant inspection of a Tauranga City Council wetland. The plant is scattered over about 1.5 hectares of pond edges and adjacent land sites.

Regional Council Manager Land Resources (Western) Robyn Skelton said the weed can grow easily from a small stem or fragment, and because of this, it is often spread within and between waterways.

“It may well have been brought to the site as a result of someone dumping the contents of a fish bowl or on contaminated machinery,” Ms Skelton said.

She said that if alligator weed established in the Bay of Plenty it could seriously impact on farming activities and block waterways. “So we have to be very careful.”

The affected pond is in Gordon Carmichael Reserve near the outdoor classroom platform and playground. The rest of the reserve’s waterways appear to be clear.

Graeme Dohnt, Tauranga City Council Drainage Services Manager said the area of infestation will be dealt with by agrichemical application and excavator.

“We may need to quarantine the pond and its surrounds by fencing it off from the public.”

Mr Dohnt asks if anyone has any clue as to where the infestation may have come from to contact the regional or city council.

A native of South America, alligator weed is easily recognised by its white, papery, clover-like flowers. Its leaves are shaped like teardrops and grow in tiers opposite each other along hollow stems. It is an aquatic perennial that forms dense floating mats on slow moving water bodies. It can hinder access to water bodies and increase the risk of flooding. As in this case, it may also establish as a terrestrial plant, invading pasture and cropping land. It can form a dense tangle of roots up to one metre deep.

Alligator weed is already widespread in Northland and has been discovered in Auckland and the Waikato. The Bay of Plenty hosts a handful of land-based sites, including one near Edgecumbe, all of which are under intensive long-term control programmes.

Ms Skelton said alligator weed is very difficult to control because of its extensive and deep root systems.

“We will be monitoring and carrying out regular control work on this new site for some years to come,” she said.