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Alligator weed is a perennial amphibious (aquatic and terrestrial) plant. It is typically bottom-rooted at the margins with floating mats which spread across the water surface, or can be deep-rooted in wet soils. The stems are hollow and buoyant; leaves are green, hairless, waxy, with a conspicuous midrib (4 x 10cm long). The flowers resemble those of white clover but are smaller and each cluster is produced on a long stalk.
Alligator weed prefers temperate climates and is found in still or slow-moving water bodies, including lakes, streams and drainage channels (also tolerating brackish water). Terrestrial habitats including pasture, cropland and gardens.
Alligator weed is very hardy and is a strong competitor, tolerating a wide range of environmental conditions and disturbance regimes, and is resistant to flooding/submergence. It prefers full sun but is more shade tolerant than typical pasture grasses, therefore may be advantaged by slight shading. Alligator weed doesn’t set viable seed in New Zealand. It reproduces vegetatively from stem nodes and root fragments with are easily spread.
Freshwater weeds are difficult to eradicate once established, but are possible to control. Before you start thooughly check the waterway's adjacent areas and inflows to see if the infestation has spread.
As most aquatic weeds grow from fragments, start control at the upstream end of the infestation. In narrow waterways you can reduce the growth of aquatic weeds with riparian planting to reduce light levels.
Land sites (do not use these chemicals over water)
Biocontrol for aquatic infestations has been released and is established in Norhtland.