Annex B - Additional Research Data

Aquatic plants scientists call water hyacinth (Eichornia crassipes and several related species) the worst aquatic plant in the world! It is native to South America but has been naturalized in most of the southern United States and in many of the world's subtropical and tropical climates. Water hyacinth plants have tremendous growth and reproductive rates and the free-floating mats cause substantial problems. Plant managers and waterfront residents spend millions of dollars per year in the United States for its management.

Water hyacinth is a popular water garden plant because of the beauty of its large, purple to violet flowers and its interesting floating vegetation. Many plant nurseries and big box stores sell it in Washington as an ornamental pond plant each spring and summer. Although weed scientists believe that water hyacinth cannot survive Washington's winters, its presence as an ornamental makes it possible for escape and growth in the wild. Water hyacinth can survive freezing conditions in other states where it is established and it may be possible for this plant to overwinter during a mild western Washington winter.

Growth Habit
Water hyacinth is a free-floating plant that gets its nutrients from the water from dangling roots. The plant reproduces by seeds and vegetatively through daughter plants that form on rhizomes and produce dense plant beds. In one study, two plants produced 1,200 daughter plants in four months. By this mechanism, water hyacinth can form impenetrable mats of floating vegetation. Individual plants break off the mat and can be dispersed by wind and water currents. A single plant can produce as many as 5,000 seeds and waterfowl eat and transport seeds to new locations. Seedlings are common on mud banks exposed by low water levels.

Management
Plant managers control water hyacinth by many methods including harvesting, application of aquatic herbicides, and biological control agents. In Washington, the best way to manage water hyacinth is to prevent it from ever becoming established. If you purchase water hyacinth at a local nursery, do not dispose of excess plants by throwing them into a lake, river, stream, or drainage ditch. A number of water hyacinth plants have been found in drainage ditches in the Longview/Kelso area in southwestern Washington. Drainage ditch managers believe that somebody with a nearby ornamental pond disposes of excess plants by throwing them into the drainage canals. University arboretum staff discovered a large infestation of water hyacinth in a backwater area on Lake Washington where somebody had either deliberately wanted to introduce water hyacinth plants or used the arboretum as a convenient place to dump excess plants. In both instances, managers immediately hand removed all water hyacinth plants from these water bodies.
Help prevent introduction of water hyacinth into Washington waters by:
  • Disposing of all excess plants on a compost heap and away from water.
  • Only planting water hyacinth into ornamental ponds and not natural water bodies. This is asking for trouble
Identification
Water hyacinth is distinctive.
  • They are floating plants with a round to oval, shiny green leaves up-to-ten inches in diameter, although smaller leaves are common.
  • Leaves are held upright so they act like sails.
  • The leaf stalk is thick and spongy and helps to keep the plant buoyant
  • A mass of fine roots hangs in the water underneath the plant
  • The flowers are large (2-3 inches) and attractive. They are blue-purple or lilac-colored with a yellow spot
Another tropical floating-leaved nursery plant, called water lettuce, may be mistaken for water hyacinth. However; water lettuce doesn't have showy flowers and has large ribbed leaves. Water lettuce is much less cold-tolerant than water hyacinth and is not thought able to survive in cold climates


Citation: Water Hyacinth (Eichhornia crassipes). (n.d.). Retrieved from http://www.ecy.wa.gov/programs/wq/plants/weeds/hyacinth.html

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