Considered very invasive and is on the Hawaii State Noxious Weed List.
- A grass that can grow up to 20 ft. tall
- Looks a little like sugarcane, but leaves are shorter and alternately arranged along stem
- Flowers are long, dense, and plume like
- Native to the Mediterranean region, introduced to Hawaii as an ornamental
- Grows well along rivers, streams, and ditch channels, where masses of plant material choke drainages and cause flooding
- Crowds out native vegetation
- Thick growth reduces habitat for wildlife
- Fire hazard when dry
- Spreads easily by root and stem fragments floating downstream and taking root
- Also spreads in dry areas when dirt containing root pieces are moved (e.g. in topsoil or on heavy equipment such as bulldozers)
- Kauai: Eight known populations, mostly on the West side. KISC is working to control these populations and encourages landowners to replace these with non-invasive alternates.
- Oahu: Several ornamental plantings. Not currently an OISC target.
- Maui: Most populations are found in areas where rapid spread is unlikely, areas such as yards, open lots and dry streambeds. However, there is a strong possibility of this plant spreading to ideal habitat such as Kealia or Kanaha Ponds if people plant it nearby, or through the movement of dirt containing root parts, or by flooding of infested streambeds.
- Molokai: Two known populations on south side have been controlled by MoMISC. Monitoring and maintenance is ongoing.
- Lanai: Presence/absence unknown
- Kahoolawe: None known
- Big Island: BIISC has no control efforts for giant reed and little is known about its distribution on the Big Island.