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Water Celery and Vietnamese Parsley

Water celery (Helosciadium nodiflorum) and Vietnamese parsley (Oenanthe javanica) – new additions to Tasman-Nelson Regional Pest Management Plan (RPMP).

Management category: Sustained control programme for whole region for both species. They are listed together for management purposes as the approach taken is the same for both plants.

Rationale for inclusion in the Tasman-Nelson RPMP

Water celery and Vietnamese parsley are in the early stages of naturalisation in Nelson City and Tasman District. While the abundance of both plants is relatively low there is a large invasion potential in regional waterways. Current infestations are beyond the eradication stage and ability. Trials to control incursions have been successful at reducing the size of infestatioins, buthave not yet proven to be able to eliminate them completely.

Both plants are best managed to reduce impacts on the biodiversity values of waterways, with obligations on occupiers ti undertake control. A ‘check, clean, dry’ tyoe rule, with awareness, will also help to reduce the soread and impacts beyond current areas.

Water celery smothering stream margins

Description and adverse effects

Water celery is an aquatic herb that appears to be reliant on human activity to disperse fragments. While not cultivated as a culinary herb it can be mistaken for watercress (Nasturtium officinale). It is widespread in the North Island, though rare in the South Island. It regrows readily from stem segments and prolific seed. It can have negative impacts on river recreational (fishing and swimming), infrastructural (drainage), and environmental (aquatic biodiversity) values by clogging small streams and waterways.

Vietnamese parsley in Poorman Valley Stream

Vietnamese parsley is an aquatic herb cultivated as an ornamental and culinary herb species. It was first recorded as successfully establishing in the wild in 2014. It regrows readily from stem segments. It impacts on river recreational (fishing and swimming), infrastructural (drainage), and environmental (aquatic biodiversity) values by clogging small streams and waterways.

Plan rules

Within the Tasman-Nelson region occupiers must:

  • Destroy any water celery and Vietnamese parsley on their land, on the written direction of an authorised person, on an annual basis, prior to the onset of flowering.
  • Remove all fragments of water celery and Vietnamese parsley from their places (i.e. machinery, equipment and craft that have been in contact with waterway vegetaton) when leaving infested waterways.

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