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Species
Information
- hydrilla
(waterthyme)
- Hydrilla
verticillata (L.
f.) Royle
- USDA
Symbol: HYVE3
- Oregon
Noxious Weed Designation: A
- Pictures
ALERT: PLEASE CALL 1-866-INVADER IF YOU SUSPECT YOU HAVE FOUND THIS SPECIES
Identification:
Perennial aquatic plant. Grows rooted to the bottom with long stems that reach water’s surface. Can be monoecious or dioecious. Leaves are 1/16 to 1/8 in wide, 1/4 to 3/4 in long and occur in whorls of five. Small, axillary leaf scales are found next to the stem and inserted at the base of the leaf, a character that distinguishes hydrilla from other family members. The nut- like turions (tubers) are a key identifying feature. Egeria densa is similar in appearence but has leaves in whorls of four and does not have turions. This species is not yet known to occur in Oregon, but does occur in Washington and California.
Impacts: Hydrilla is the most serious threat to aquatic ecosystems in temperate climate zones. Dense stands of hydrilla provide poor habitat for fish and other wildlife altering water quality by raising pH, decreasing oxygen, and increasing temperature. Stagnant water created by mats provides good breeding grounds for mosquitoes. Hydrilla interferes with recreational activities such as swimming, boating, fishing, and water skiing and will clog irrigation ditches and intake pipes.
Biological
Controls: Biological control agents are not used on "A" listed weeds in Oregon. If this weed is found in the state it will be managed for eradication or containment. Four approved biological control agents are available for control of hydrilla, but none of them are established in surrounding Pacific Northwest states.
Oregon
Maps of Hydrilla Distribution
Links:
USDA
Plants Database information on hydrilla
GRIN
Database information on hydrilla
Oregon Department
of Agriculture information on hydrilla
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