Family: Poaceae

Origin, Description & Uses:
Urochloa decumbens, commonly known as signal grass or Surinam grass, is a perennial grass native to Africa. It was introduced to many tropical and subtropical regions as a valuable forage grass because of its vigorous growth, tolerance of grazing, and ability to establish on poor soils. It has also been widely planted for erosion control on slopes and disturbed areas. Signal grass has since spread beyond cultivation and is now naturalized on Kauaʻi, Maui, and Hawaiʻi Island, with populations considered potentially naturalizing on Oʻahu and Kahoʻolawe.

Risks & Threats:
Although useful as a pasture species, Urochloa decumbens is naturalized in Hawaiʻi and possesses traits that are cause for concern. Its rapid growth, abundant seed production, and ability to persist under grazing allow it to spread into disturbed sites and surrounding natural areas, where it can form dense stands that displace native vegetation and alter tropical island ecosystems. Because this species is already established in parts of the state, landowners and land managers should avoid planting it in areas where it is not yet widely established and take steps to prevent its further spread. When selecting grasses for landscaping, erosion control, or pasture, choose a low-risk or native alternative whenever suitable options are available.

High Risk Traits:

• Broad climate suitability
  
• Thrives and spreads in regions with tropical climates
  
• Naturalized on Kauai, Oahu, Molokai, Kahoolawe, Hawaii (Hawaiian Islands) and elsewhere
  
• A weed of gardens, parks, roadsides, disturbed sites, waste areas, creek-banks (i.e., riparian areas), open woodlands and plantation crops
  
• An environmental weed, impacting native vegetation in Brazil and Australia
  
• Other Urochloa species are invasive
  
• Allelopathic
  
• Potentially toxic or harmful to grazing animals under certain growing conditions
  
• Tolerates many soil types
  
• Forms a dense cover that can exclude other vegetation
  
• Reproduces by seeds and stolons
  
• Apomictic
  
• Seeds dispersed by water, animals, as a produce contaminant, by ants, and intentional cultivation
  
• Prolific seed production
  
• Tolerates heavy grazing and fire

Low Risk Traits:

• Despite naturalization, negative impacts have not been reported from the Hawaiian Islands to date
  
• Unarmed (no spines, thorns, or burrs)
  
• Palatable to grazing animals
  
• Seeds lose viability after 5 months (do not form a persistent seed bank)
  
• Herbicides may provide effective control