Family: Asteraceae

Origin, Description & Uses
Hairy fleabane (Erigeron bonariensis, also known as Conyza bonariensis) is a fast-growing annual herb native to South America. It is now widely distributed in tropical and subtropical regions around the world, including across the Hawaiian Islands. This species typically grows upright, producing slender stems covered in fine hairs and narrow leaves, with small, tufted flower heads that range from white to pale purple. Hairy fleabane commonly colonizes disturbed areas such as roadsides, agricultural lands, and open fields. While not widely cultivated as an ornamental, it has occasionally been used in traditional herbal practices and is sometimes considered a minor component of ruderal vegetation.

Risks & Threats
Hairy fleabane is naturalized throughout Hawaiʻi and possesses traits that are cause for concern. It produces large quantities of wind-dispersed seeds, allowing it to spread rapidly and establish dense populations in disturbed and natural areas alike. This aggressive growth can outcompete native vegetation, alter plant community structure, and interfere with agricultural productivity. In addition, it has shown the ability to develop resistance to herbicides in other regions, making management more difficult. Because of these characteristics, it could detrimentally impact tropical island ecosystems.

High Risk Traits:

• Broad climate suitability
  
• Thrives in tropical climates
  
• Widely naturalized
  
• Crop weed (esp. no-till crops)
  
• Other Erigeron and Conyza species are invasive
  
• May possess allelopathic properties
  
• May be an allergen to susceptible individuals
  
• Tolerates a wide range of soil conditions
  
• Able to form dense thickets
  
• Reproduces by seeds
  
• Hybridizes with other species
  
• Capable of self-pollination
  
• Annual to biennial (able to reproduce in one growing season)
  
• Seeds dispersed by wind, soil movement, water and human activities
  
• In rare instances, avian seed predators and mammals may internally disperse seeds
  
• Prolific seed production
  
• Seeds can remain viable in the soil for up to 3 years
  
• Herbicide resistance has developed in a number of locations

Low Risk Traits:

• Impacts to the natural environment and ecological processes has not been documented and may not be as significant as impacts to crops
  
• Unarmed (no spines, thorns or burrs)
  
• Palatable to browsing and grazing animals
  
• Not reported to spread vegetatively
  
• Minimum tillage provides effective control