Scientific name: Ageratina adenophora
- 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.
- Mexican devil has upper stems, flower and leaf stalks densely covered in stalked glandular (sticky) hairs
- Leaves are diamond-shaped, with irregularly round-toothed edges, and in opposite pairs along the stems
- From August to December the flowers appear in dense clusters, each flower 5-7 mm across, followed by 5-angled black seeds about 1.8 mm long
- Like mistflower it is poisonous and usually avoided by livestock.
- Mexican devil 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
- It is commonly found in forest margins and clearings, waste places, scrubland and along stream sides, but rarely in swamps. It is common north of Auckland and found in areas south of Auckland, especially on the Coromandel Peninsula.
- 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 plants with fibrous roots.
- In some countries Mexican devil has been considered useful for providing some protection from erosion.
Impact on the natural environment
- Mexican devil has 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
- It is poisonous to livestock. It has been reported that Mexican devil has caused lung lesions in horses.
- Small infestations can be dug or pulled out, leaving the roots exposed so they dry out.
- Mexican devil 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
- It is 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.
- The gall fly Procecidochares utilis has been introduced as a biocontrol agent for Mexican devil, but this insect has been found to be parasitised, which has reduced its potential value as a biocontrol agent.