Identification: This bunch grass has narrow, deep green leaves and flowering stalks that grow up to 4 m (13 ft) tall. The FLOWER STALKS tower THREE TIMES HIGHER THAN the FOLIAGE and bear LARGE FLOWER PLUMES 300 - 600 mm (24 - 31 in) long and a cream to pinkish color. Young, non-flowering pampas plants can be distinguished by their curling, CORKSCREW SHAPED LEAVES.
Impacts: Seeds can remain viable for at least six years. Plants crowd out native plants, impede access, damage grazing lands, and create fire hazards. The invasive nature of C. selloana was historically not recognized in Hawai‘i because only female plants were cultivated and sold. This species generally requires cross-pollination between male and female plants to produce viable seeds. The introduction and spread of male plants has caused an explosion of this species in California and New Zealand. Maui is set up for a similar situation.
Dispersal Mechanism: Pampas seeds are spread by wind traveling up to twenty miles away from the parent plant. Humans also disperse seeds with contaminated gear. Flower plumes are sold for dried flower arrangements. Pampas grass is currently being managed on Maui where wildland naturalized populations have established from residential plantings. All known populations have been removed from Kauai and Lanai. Please help spread the word about this pest plant and report all new locations.

More information about this pest 

Pampas grass look-alikes:

Native Hawaiian sedges (family Cyperaceae):
Some of the native Hawaiian sedges can be confused with young pampas grass. Native Hawaiian sedges do not produce corkscrew leaves, the saw-like sharp leaf edge, tall flowering stalks, and large showy seed plumes like pampas grass.