Nonindigenous Aquatic and Semi-Aquatic Plants in Freshwater Systems

Nonindigenous Aquatic Plants

Napier Grass, Elephant Grass (Pennisetum purpureum) Schumach.

Napier grass or elephant grass (Fig. 17) is semi-aquatic and native to the warm climates of Africa but is now common worldwide between latitudes 23 N and 23 S (Holm et al. 1977). It is extensively grown for forage in Central America (Gould 1968) and for this purpose was introduced in Texas and in southern Florida (Schardt and Schmitz 1990).

Napier grass is now established throughout southern Florida, especially along canal and ditch banks and in other disturbed areas. It is less common in central to northern Florida because it is susceptible to freezes. Napier grass populations were in 13 public lakes and rivers during 1990, covered 9 ha, and ranked 102nd in abundance of all observed aquatic species (Schardt and Schmitz 1990).

Napier grass is a large, upright perennial that grows to a height of approximately 4 m (Godfrey and Wooten 1979). It is a rapid colonizer of disturbed areas and prospers in a broad range of conditions. It tolerates periods of inundation and drought and fire, although it grows best in rich, well-drained soils (Schardt and Schmitz 1990). It is a forage plant of considerable importance in some parts of the world (Bajaj and Dhanju 1980) but also one of the world's worst weeds (Holm et al. 1977). Dense, impenetrable forests can quickly form after Napier grass gains a foothold. Napier grass is rarely a problem along lake and river shores but causes difficulties for flood control, especially in southern Florida. Plants block access to waterways, reduce water flow, and can overgrow pumping stations. Biological controls for napier grass are unknown in Florida. Mowers and draglines are used for mechanical control. The herbicide glyphosate provides acceptable control in aquatic sites (Schardt and Schmitz 1990).