Family: Asteraceae

Ageratum conyzoides, commonly known as billygoat-weed, maile hohono, or whiteweed, is a fast-growing annual herb native to tropical regions of the Americas. It is widely distributed across the tropics and subtropics and has become invasive in many parts of the world. This plant produces clusters of small, fluffy, bluish-purple to white flowers and emits a strong odor when crushed. In Hawaiʻi, it is sometimes called maile hohono (“foul-smelling maile”) because its scent is unpleasant compared to the fragrant native maile vine. Ageratum conyzoides reproduces readily from its abundant seeds, which are dispersed by wind, animals, and human activity, allowing it to quickly colonize disturbed areas, roadsides, and pastures.

This species is considered a serious agricultural weed because it competes aggressively with crops and pasture grasses, reduces yields, and can harbor pests and plant pathogens. In natural areas, billygoat-weed has the potential to displace native vegetation and alter ecosystems by forming dense stands that exclude other plants. Its rapid spread and adaptability make it difficult to manage once established. While sometimes used in traditional medicine or as an ornamental, the negative impacts of Ageratum conyzoides far outweigh its limited benefits in Hawaiʻi.

High Risk Traits:

• Broad climate suitability and elevation range exceeds 1000 m, demonstrating environmental versatility
  
• Thrives in tropical climates
  
• Widely naturalized, including all main Hawaiian Islands
  
• Disturbance-adapted weed of crops
  
• Environmental weed
  
• Other Ageratum species are invasive
  
• Allelopathic
  
• Unpalatable and toxic to animals
  
• Toxic and allergenic to people
  
• Alternate host of crop pests and pathogens
  
• Tolerates shade
  
• Tolerates many soil types
  
• Forms dense stands in crop lands
  
• Reproduces by seeds and vegetatively
  
• Self-compatible
  
• Reaches maturity rapidly (as early as 2 months from seed)
  
• Seeds dispersed by wind, water, and attached to on the hairs of livestock and wild animals, clothes and agricultural machinery
  
• Prolific seed production

Low Risk Traits:

• Unarmed (no spines, thorns or burrs)
  
• Used medicinally
  
• Seeds are non-dormant and might not form a long-lived seed bank
  
• Controlled effectively by mechanical and chemical means