What does it look like?
Mist flower is an erect or sprawling, many‑stemmed herb or subshrub that grows about 0.5–1.5 metres tall. It has a perennial fibrous root system. Stems are usually purple, covered in purple‑striped, non‑sticky hairs, and become woody as the plant ages. The stems branch in opposite pairs and may die back in winter.
The willow‑like leaves grow in opposite pairs and are 60–100 mm long and 15–25 mm wide. They are coarsely serrated, except near the base. Small white flowers form in clusters from August to January, followed by black, five‑angled seeds about 2 mm long. Mist flower can be confused with a similar species, Mexican devil (Ageratina adenophora).
It grows very densely and overtops groundcovers, is long-lived, quick-maturing, and produces a large number of highly viable, well-dispersed (probably short-lived) seed. Drooping stems can also take root in wet sites wherever they touch the ground. Tolerates deep shade and damp, damage and grazing, salt, and most soil types, but is limited by dry conditions and frost. Poisonous, so usually shunned by livestock.
It grows in damp forest and margins, intact or disturbed bush, light gaps, shrublands, wetlands, streamsides, river systems, inshore and offshore islands, slips, alluvial flats, coastal and estuarine areas, and occasionally places where low growing epiphytes would usually grow.
Why is it a problem?
Mist flower forms very dense colonies, preventing the seedlings of native species from establishing in a wide range of habitats, especially riparian areas. It invades strips along waterbodies, replacing vulnerable species, causes sediment buildup in streams, impeding flow, degrading habitats, and causing flooding, and can also cause instability on steep sites.
Seed is spread long distances by wind and is also spread by water. Seed sources include roadsides, rivers, quarries, plantation forest, and reverting pasture.
Control methods
Physical control
Dig or pull-out small infestations (summer): Expose roots. These will resprout if roots (occasionally even stems) touch damp soil and/or seed bank reinfests bared ground.
Herbicide control
Spray (spring-summer) using glyphosate (20ml/L + penetrant). Or,
Spray (spring-summer) using metsulfuron-methyl 600g/kg (20g/100 L (spraygun) or 3g/10L (knapsack)). Add penetrant in winter. Spray lightly, not to run off. Avoid water contamination.
CAUTION: When using any herbicide or pesticide, PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and safety requirements are followed.
Biological control
Biocontrol of mist flower has been hugely successful in New Zealand. Two biocontrol agents used successfully in Hawaii were chosen for New Zealand: mist flower fungus (Entyloma ageratinae), released 1998; and mist flower gall fly (Procecidochares alani), released 2001.
More information
Also known as Mistweed, it looks similar to Mexican devil (Ageratina adenophora).
Related links
