Eichornia crassipes - Water Hyacinth - A Probem Aquatic Plant in the Western USA

Water Hyacinth Flowers

The Western Aquatic Plant Management Society

Description and Variation

Water hyacinth is a member of the pickerelweed family (Pontederiaceae).

Water hyacinth are distinctive-looking plants.

They are floating plants with 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 hang 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.
The fruit is a three-celled capsule containing many minute, ribbed seeds.

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.

Economic Importance

Water hyacinth is listed as one of the most productive plants on earth and is considered one of the world's worst aquatic plants. It forms dense mats that interfere with navigation, recreation, irrigation, and power generation. These mats competitively exclude native submersed and floating-leaved plants. Low oxygen conditions develop beneath water hyacinth mats and the dense floating mats impede water flow and create good breeding conditions for mosquitoes. Water hyacinth in Florida

Water hyacinths are a severe environmental and economic problem in all of the gulf coast states and in many other areas of the world with a sub-tropical or tropical climate. This species has rapidly spread throughout inland and coastal freshwater bays, lakes, and marshes in the United States and in other countries.

With the increasing popularity of water gardening and home ponds, water hyacinth is now sold by many western nurseries for its unusual appearance, attractive flowers, and ability to remove nutrients from the water. Water hyacinth is thought to be cold-sensitive and unable to survive temperatures below 20 degrees F. However, water hyacinth should never be deliberately introduced to lakes, rivers, streams, or drainage ditches.

Geographic Distribution

Water hyacinth originated in tropical South America, but has become naturalized in many warm areas of the world: Central America, North America (California and southern states), Africa, India, Asia, Australia, and New Zealand.

Habitat

Water hyacinths grow over a wide variety of wetland types from lakes, streams, ponds, waterways, ditches, and backwater areas. Water hyacinths obtain their nutrients directly from the water and have been used in wastewater treatment facilities. They prefer and grow most prolifically in nutrient-enriched waters. New plant populations often form from rooted parent plants and wind movements and currents help contribute to their wide distribution. Linked plants form dense rafts in the water and mud.

The fibrous root system of water hyacinth provides nesting habitat for invertebrates and insects. Leaf blades and petioles are occasionally used by coots. However, whatever benefits this plant provides to wildlife are greatly overshadowed by the environmental invasiveness of this noxious species.

History hyacinth_flower.jpg (28813 bytes)

It is believed that the water hyacinth was introduced first into the United States at the World's Industrial and Cotton Centennial Exposition of 1884-1885 in Louisiana. A Florida visitor to the Exposition apparently returned home with water hyacinth plants and subsequently released them into the St. Johns River. From there water hyacinth plants rapidly spread to neighboring states.

Growth and Development

The following is a description of the water hyacinth life cycle in the southern United States (Vicksburg, Mississippi). In spring overwintering plants (old stem bases) initiate growth by producing daughter plants. These plants slowly increase in number and size during the spring and summer until the maximum biomass is reached in September. As the plants become crowded, many of the lower leaves die back due to shading. Water hyacinths are in full bloom in late summer and early fall. (Florida plant managers report that water hyacinths flower year-round). Seeds form in the submerged, withered flower. By late fall some of the old leaves start dying and by January most plants have senescensed.

Colonization of a new site begins with small plants at low plant densities. These plants increase in number and density without increasing in size until they produce a new mat. As a mature dense mat is formed, individual plant size continues to increase, but density decreases as the result of intraspecific competition.

Reproduction

Water hyacinth reproduces sexually by seeds and vegetatively by budding and stolen production. Daughter plants sprout from the stolons and doubling times have been reported of 6-18 days. The seeds can germinate in a few days or remain dormant for 15-20 years. They usually sink and remain dormant until periods of stress (droughts). Upon reflooding, the seeds often germinate and renew the growth cycle.

Response to Herbicides

The use of herbicides to control water hyacinth is common. Westerdahl and Getsinger report excellent control of water hyacinth by the use of the aquatic herbicides 2,4-D, diquat, and a combination of diquat and complexed copper. Fair control of water hyacinth is obtained with endothall dipotassium salt, endothall dipotassium salt and complexed copper, endothall dimethylalkylamine salts, and glyphostate.

Response to Mechanical Methods

Mechanical controls such as harvesting have been used for nearly 100 years in Florida, but are ineffective for large scale control, very expensive, and cannot keep pace with the rapid plant growth in large water systems.

Biocontrol Potentials

Three insects have been released for the biological control of water hyacinth. These include two weevil species (Neochetina spp.) and a moth (Sameodes albiguttalis). Unfortunately large scale reductions in water hyacinth populations did not occur. Instead insect predation reduced plant height, decreased the number of seeds produced, and decreased the seasonal growth of the plants. This, in turn, allowed better boat access into plant mats, reduced use of herbicides, and resulted in less plant problems. In Louisiana, the seasonal growth of water hyacinth was reduced from a high of over 400,000 hectares per year to lows of only about 80,000 hectares.

References

Grodowitz, M.J. 1998. An Active Approach to the Use of Insect Biological Control for the Management of Non-Naive Aquatic Plants. Journal of Aquatic Plant Management. 36:57-61.

Westerdahl, H.E. and K.D. Getsinger, eds. 1988. Aquatic plant identification and herbicide use guide, volume II: Aquatic plants and susceptibility to herbicides. Technical report A-88-9. Department of the Army, Waterways Experiment Station, Corps of Engineers, Vicksburg, MS.