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 Water lettuce (Pistia stratiotes) is a free-floating aquatic
plant, native to Asia, Africa and equatorial America. It is believed to have been
introduced into Australia as an ornamental aquarium plant. It is a declared
noxious weed in most Australian states and territories.
 IDENTIFICATION
As the
name suggests, the plant resembles a small, floating, open head of
lettuce. The aquatic
perennial is spongy and
consists of a floating rosette of pale green, fan-shaped leaves covered with
hairs. It has a tuft of unbranched, fibrous roots up to 80 cm long.
 THE PROBLEM
Once established, water lettuce can spread to form a dense, obstructive mat,
covering an entire body of water. Wetlands, lakes, reservoirs and
slow moving rivers/streams are most at risk from this weed, especially in the
warmer parts of the State. These large dense
floating mats can have negative impacts on native aquatic plants and animals.
They can also interfere with irrigation, boating and water sport activities.
Thick mats of water lettuce are also known to harbour disease-causing mosquitoes.
LEGAL REQUIREMENTS
Water lettuce is a declared CLASS 1 NOTIFIABLE NOXIOUS WEED throughout New South
Wales. Any findings must be reported to the local council within 3 days of
detection. It is also declared in Queensland.
OPTIMUM TIME TO TREAT
Plants can be retrieved from the water at any time of the year. Chemical
treatment not usually suitable during winter period.
CONTROL ALTERNATIVES
Non-chemical:
Physical removal is slow but very effective. Plants removed from the water will
dry out and die. Chemical: Herbicide include diquat, 2,4-D acid and
glyphosate 360 g/L of a type registered for use in waterways.
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North West Weeds
