Mistflower is an aggressive ground cover species that forms dense mats of growth on forest floors and along stream sides. It prefers a damp, shady environment and in these areas it can impede the growth of native ground cover species and prevent the establishment of many native seedlings. If uncontrolled this plant pest can completely dominate native vegetation and modify the composition of native forest and stream side environments. Mistflower (Ageratina riparia) is a native of Central America and was introduced to New Zealand as an ornamental plant in the 1930s.
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What it looks like
Mistflower is an erect or sprawling perennial herb, which may grow up to one, or occasionally two metres tall with numerous purple stems.
Leaves: Oval, about 7cm long and 2cm wide. Serrated on the upper edges.
Flowers: White and grow in small clusters off long stems.
Seeds: Dark brown to black with fine white hairs on the tips. Each plant can produce 10,000 to 100,000 seeds which are dispersed by wind or water.
Mistflower inhabits forest margins, clearings, waste lands, damp banks, wetlands, damp forests and especially streamsides. Small slips on river and stream edges are especially vulnerable.
Where you can find it
There are known sites of mistflower on the northern end of the Coromandel Peninsula, the border area of the Coromandel, and Kaimai Ranges, and in the Hauraki District.
Responsibility for control
Our Regional Pest Management Strategy aims to control known sites and prevent further establishment of this plant pest, using two biological control agents:
- mistflower fungus
- mistfower gall fly.
The sale, propagation or distribution of mistflower is prohibited.
Biological control involves the importation of insects or fungi that feed on these plants in their native countries. A national Biological Control Programme is run by Manaaki Whenua – Landcare Research.
Waikato Regional Council supports the national programme, and maintains a local Biological Control Programme for the Waikato region.
A biological control project for mistflower is being jointly funded by the Auckland, Northland and Waikato (Waikato Regional Council) Regional Councils and the Department of Conservation. For up-to-date information on this project, contact your Biosecurity Plant Pest Contractor.
Mistflower can be controlled mechanically, however it is essential the plants are replaced with suitable species (for example, native twining legume species) soon after removal as re-infestations will occur.
Individual plants can be grubbed or hoed, larger infestations can be removed by slashing or ploughing. In difficult terrain, mechanical control is best combined with chemical treatment.
Mistflower can be resistant to repeated use of herbicides. Information about possible herbicides suitable for your situation can be obtained from your Biosecurity Plant Pest Contractor.
For further information and advice contact your local Biosecurity Plant Pest Contractor.
Other pest plant publications.
- Visit our Waikato Regional Pest Management Strategy
- 'What makes a pest a pest? - A guide to Waikatos pest management future' Pick up, download or order for free from our offices.
- 'Plant me instead - Plants to use in place of common pest plants'. Pick up or order for free from our offices.
- Download the National Pest Plant Accord.
- 'Poisonous plants and fungi in New Zealand - A guide for parents, schools and child minders'. Pick up or order for $15 from our offices.