Hydrilla verticillata
(L. f.) Royle (Hydrilla ) |
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Family: Hydrocharitaceae (Tape-Grass Family) Synonym(s): Duration: Perennial Habit: Submerged aquatic
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Description: Hydrilla is a submersed typically rooted perennial plant that can form monospecific stands with dense mats at the surface. Its heavily branched stems can grow up to 9 m (30 ft) long. Leaves are simple and arranged in whorls of 4-8 leaves around the stem. The leaves are small, 2-4 mm (0.1-0.2 in) wide and 6-20 mm (0.2-0.8 in) long, and pointed. The finely serrated edges and typically 1-4 small bumps or teeth along the underside midrib are diagnostic. The whitish or translucent 3-petaled-&-3-sepaled flowers are tiny, only 1.5-3.0 mm (0.0625-0.125 in) in diameter, and float on threadlike stalks that are up to 10 cm (4 in) long. History: Hydrilla was first introduced into North America in the mid to late fifties by the aquarium trade. California officials have also traced hydrilla infestations to shipments of mail order waterlilies. Once introduced and established, hydrilla is easily spread through boating and fishing activities and by waterfowl. Hydrilla tubers are readily consumed and regurgitated tubers have been shown to be viable. Biology & Spread: In Texas, only the female dioecious form (plants with only single-sex flowers) is found and, consequently, seeds are not produced. Hydrilla produces tubers, which facilitate overwintering, as well as turions that can remain viable in the sediment for up to four years. Ecological Threat: Hydrilla forms monospecific stands, often outcompeting and replacing native submersed vegetation. Dense underwater stands of hydrilla raise water pH and temperature, and lower dissolved oxygen. While the number of fish is often increased, large fish may become rarer. Hydrilla infestations can promote mosquito habitat. This invasive plant has the potential to affect power generation and agricultural irrigation by blocking intakes and impedes water flow. US Habitat: Hydrilla is found in lakes, rivers, reservoirs, ponds, and ditches. It tends to form monospecific stands that can cover hundreds of acres. Hydrilla can be found in depths of greater than 20 feet where water clarity is good. Increased water clarity in lakes with invasive zebra mussels (Dreissena polymorpha) can allow hydrilla to grow to greater depths, exacerbating infestations. Distribution
Resembles/Alternatives: Native Texas alternatives include Management: Scientific research and 30 years of practical experience by aquatic plant managers using herbicides, biological agents, mechanical removal, and physical habitat manipulation have produced relatively successful management programs in Florida and other states. However, in spite of long-term intensive management efforts, hydrilla is still a major weed problem in the states where it has become well-established. Physical removal of hydrilla can be effective in small areas such as boat slips but treatments with herbicides are necessary to control extensive infestations. Care should be taken during physical removal; fragmentation promotes spread. Water drawdowns can be effective for management. Because hydrilla is prohibited in Texas, a permit may be required for physical removal. A nuisance aquatic vegetation treatment proposal is required for chemical, physical, or biological control of any aquatic plant species on a public water body. USE PESTICIDES WISELY: ALWAYS READ THE ENTIRE PESTICIDE LABEL CAREFULLY, FOLLOW ALL MIXING AND APPLICATION INSTRUCTIONS AND WEAR ALL RECOMMENDED PERSONAL PROTECTIVE GEAR AND CLOTHING. CONTACT YOUR STATE DEPARTMENT OF AGRICULTURE FOR ANY ADDITIONAL PESTICIDE USE REQUIREMENTS, RESTRICTIONS OR RECOMMENDATIONS. MENTION OF PESTICIDE PRODUCTS ON THIS WEB SITE DOES NOT CONSTITUTE ENDORSEMENT OF ANY MATERIAL. Listing Source
Text References
Data Source Last Updated: 2019-08-30 by Monica McGaritty, TPWD |
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