Scientific name: Ageratina riparia
- Bushy, woody, many-stemmed, colony-forming perennial with fibrous woody stock
- Stems usually covered in hairs, become woody with age, and have branches in opposite pairs.
- Mistflower has purple coloured upper stems
- Flower and leaf stalks densely covered in pale hairs without glands
- Leaves are lance-shaped, coarsely segmented and in opposite pairs along the stems
- Branches occasionally die back in winter
- Between August and January plants bear clusters of small white flowers, each 4-5 mm across, followed by black, 5-angled, 2 mm long hairy seeds
- Like Mexican devil, mistflower is poisonous so is usually ignored by livestock.
- Mistflower originally came from the Americas; mistflower from Mexico and the West Indies and Mexican devil from South America
- It was first recorded here in 1931, probably introduced as attractive garden plants
- Mistflower forms very dense colonies in damp forest margins and clearings, in waste places, on damp banks and along stream sides. It is especially common in North Auckland but also found south of Auckland, and in Lower Hutt and Wellington City
- Seeds have a small pappus and can be spread by air currents and by water. They can also be moved by animals or when soil is transferred from place to place
- It is a perennial plant with fibrous roots.
- Mistflower has apparently been used as a tanning agent and in the past as an ornamental garden plant
- In some countries it has been considered useful for providing some protection from erosion.
Impact on the natural environment
- Mistflower become important invasive weeds in many parts of the world
- It forms dense colonies that prevent the establishment of seedlings of native plant species. It replaces more useful plants on the edges of waterways and can impede drainage.
Impact on stock
- Mistflower is poisonous to livestock.
- Small infestations can be dug or pulled out, leaving the roots exposed so they dry out.
- Mistflower is readily controlled by a number of herbicides but as they frequently grow in areas where access and use of spray equipment is a problem, chemical control is often not an option.
- Weed wiping with glyphosate or metsulfuron-methyl is effective at any time of the year
- Spraying in the summer months with glyphosate plus penetrant is effective
- Spraying with metsulfuron-methyl is also effective, but in winter is more effective if a penetrant is added. Spraying should be done lightly so that none of the spray runs off the treated plants
- They are also readily controlled in pasture with 2,4-D ester, triclopyr and picloram. Note however that these herbicides are also damaging to clovers to a lesser or greater extent
- ALWAYS READ PRODUCT LABELS BEFORE APPLYING: Consult your farm consultant, industry rep or the New Zealand Agrichemical Manual for more information about chemical control.
- Mistflower has been successfully controlled by the introduction of two biocontrol agents that had been very successful in controlling the same weed in Hawaii
- The white smut fungus Entyloma ageratinae was released in New Zealand in 1991, and the gall fly Procecidochares alani in 2001. Between them they have severely reduced the incidence of mistflower
- Native plant species have recovered following effective control of mistflower.