Non-native Invasive Freshwater Plants

Water Hyacinth (Eichornia crassipes)

Technical Information

Description

Water hyacinth (Eichornia crassipes) is a member of the pickerelweed family (Pontederiaceae). The plants vary in size from a few centimeters to over a meter in height. The glossy green, leathery leaf blades are up to 20 cm long and 5-15 cm wide and are attached to petioles that are often spongy-inflated. Numerous dark, branched, fibrous roots dangle in the water from the underside of the plant. The inflorescence is a loose terminal spike with showy light-blue to violet flowers (flowers occasionally white). Each flower has 6 bluish-purple petals joined at the base to form a short tube. One petal bears a yellow spot. The fruit is a three-celled capsule containing many minute, ribbed seeds.

Economic Importance

Water hyacinth is listed as one of the most productive plants on earth and is considered the world's worst aquatic plant. 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 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 Washington 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. While there is no direct evidence that water hyacinth can over winter in the wild in Washington, it should never be deliberately introduced to lakes, rivers, streams, or drainage ditches. If a cold-resistant ecotype should develop, the species may become capable of surviving western Washington winters. Because water hyacinth reproduces sexually by seeds, the chances are higher of developing a cold-tolerant ecotype than if it reproduced only vegetatively.

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. We have no evidence that water hyacinth has established in the wild in Washington, although it is being sold at most aquatic plant nurseries. In 2000 a site was discovered in southeastern Washington where hyacinth had over wintered. However, the site consisted of small ponds that were receiving waters from an industrial process. Company officials indicated that the water temperatures remained warm throughout the winter. 

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.

In the Pacific Northwest, water hyacinth is planted outdoors in ponds and in aquaria, but it is not considered winter hardy, except under special conditions. 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

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 it spread 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 reports 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 senescenced. 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 or diquat.

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.

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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.

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