Water hyacinth

Eichhornia crassipes

Background

Identification

• Free-floating on surface of water, bushy, fibrous roots, often in large mats measuring tens or hundreds of feet in diameter. Can appear to be rooted in mud.
• Round or oval shiny green leaves, 3 to 8 in. across; buoyant bulbs at base of leaf stalk.
• Pale blue, purple to whitish flower with 6 petals.

Identification key in: Hickman, J. ed. 1993. The Jepson Manual: Higher Plants of California. University of California Press.

Growth and spread

• Multiplies and spreads rapidly; in ideal conditions grows faster than any other known plant. New individuals can sprout from pieces of runners, and in as little as a week the number of individuals can double. Also reproduces by seed. Seeds typically sink into sediment and can remain viable for 15 to 20 years.
• Obtains nutrients directly from the water.
• Stout leaves act as sails, aiding rapid spread.

Habitat

• Native to Central/South America; released into the St. Johns River, Florida about 1885.
• Local distribution includes freshwater and brackish ponds and sloughs of the Delta and North Bay. Mats of hyacinth are seen floating downstream at certain times of year.

Impacts

• Dense contiguous mats create navigation and safety concerns in waterways, harbors, and marinas.
• Interferes with irrigation and power generation by clogging pumps and siphons.
• Can completely exclude native floating and submerged vegetation, shade habitat, change water temperature.
• Can deplete dissolved oxygen.

Prevention and Control

Prevention

• Invasive plant awareness and regular monitoring is critical to identify and stop a new invasion before it takes off.
• Inform the public and any boat launch area staff of the need to remove all plant debris from boats and equipment at the ramp area after each use. The California Department of Boating and Waterways (CDBW) has developed educational resources for boaters (CDBW 2003b).
• Inform the public to never dump aquarium contents into a natural water body; legislation to ban the sale of hyacinth as an aquarium or pond plant may reduce its spread.

Manual or mechanical control

(Huff 2000)

• Mechanical removal—may be successful for small, isolated areas, such as ponds and lakes; to eliminate the risk of resprouts, all plant fragments must be removed.
• Estimated costs: harvesting costs range from $500-800 per acre, with additional costs for mobilization and equipment ($35,000-110,000) (WSDE 2001); there may be additional fees for disposal of plant material.
• Floating barriers—used to contain plant within an area.
• Suction Dredging—efforts have included drying and burning of removed plant material.
• Estimated costs: vary depending on plant density, equipment used, and transport fees for the removal of dredged material; costs for contract divers and dive tenders range from $1,200-2,400 per day, with additional fees for dredged material removal (Gibbons et al. 1999).
• Manual removal—may be useful for small areas, but is time and labor intensive.
• Estimated costs: vary depending on if volunteers conduct removal and on the plant density; if divers and dive tenders need to be contracted, costs may range from $500-2,400 per day (Gibbons et al. 1999). There may be additional fees for disposal of plant material.

Biological control

• CDFA tested water hyacinth-eating weevils (Neochetina spp.) and a moth ( Sameodes albiguttalis) at selected sites in the Delta, but results were less successful than expected, in part due to colder winter temperatures (CDBW 2003a; Huff 2000; WAPMS 2003).

Chemical control

• Application of herbicides—CDBW applies glyphosate (Rodeo®) and 2,4-D in the Sacramento-San Joaquin Delta and tributaries (Godfrey 2000).
• Estimated costs: vary depending on size of treatment area, scale of treatment, and herbicide dosage; costs per acre for materials and application by a contractor are approximately $250 for glyphosate and may range from $700-1,000 for 2,4-D. It is recommended to contract a licensed professional for herbicide applications (Gibbons et al. 1999).

Integrated control

• For control of larger infestations, mechanical removal prior to growth period, followed by herbicide application is effective (Huff 2000).

References and more information