Environment Waikato has found infestations of an aggressive water weed on eight properties at Te Kowhai, this week’s Biosecurity Committee meeting was told.

Senegal tea, a native of central and South America and was brought to New Zealand as an ornamental plant for ponds and aquariums. Only a few isolated infestations were known in the Waikato and all had eradication programmes underway.

Biosecurity officer Wendy Mead said the plant was extremely aggressive and inhabited wetlands and still or flowing water, forming dense floating mats which quickly covered water and smothering submerged native plants. It could also change habitats and displace traditional Maori food sources and interfere with boating and other water uses.

The new infestation was discovered through a landowner seeing publicity about alligator weed spreading and reporting what they thought was alligator weed in their stream. The plant had spread from an artificial pond which had previously been a wholesale nursery, and many other exotic plants were growing. Where a digger had been used to clear a drain the Senegal tea plants were actively growing on the ground.

The infestation was sprayed and effectively controlled where access was good but was not effective where access was difficult and where rain disrupted the operation. A second spray was done in late January and effectively stopped the plant seeding this year, but ongoing effort would be needed to reduce the infestation and eradicate it, she said.