Identification:
Giant reed has naturalized on Maui, but is currently only known to grow in a few locations on Molokai (see Maui map  and Molokai map.) This large, clump forming grass grows up to 8 m (16 ft) tall. HOLLOW STEMS. STIFF LEAVES with small hairs on margins which are felt when the leaf is rubbed in the wrong direction. LONG LEAVES grow to up to 70 cm (2 ft) long in an alternate pattern in a SINGLE PLANE. LARGE PLUME SHAPED FLOWERS up to (1 m) 3 ft in length develop between March and September. Forms thick masses of scaly rhizomes (horizontal underground roots.) Grows in wet areas.

Characteristics:
More information about this pest 

Giant reed look-alikes:

Sugar Cane (Saccharum officinarum:
The tall grass (3 - 5 m) is grown as a crop on Maui. The stalk of this grass grows to 3 - 5 m (10 - 16 ft) tall with a SOLID STEM. Sap of plant sweet to taste.

Elephant Grass or Napier Grass (Pennisetum purpureum):
This tall grass is commonly found growing on roadsides and waterways around Maui County. Grows in large clumps with stems up 3.6 m (12 ft) tall. Older stems appear woody. Younger growth will often have blue to purple colored nodes. This grass produces tan bottle-brush-like flowers, much smaller than the giant reed. Leaves grow up to 50 cm (20 in) long and have rough edges which are felt when the leaf is rubbed in the wrong direction. LEAF MIDRIB strongly ridged.