| Identification
Hydrilla is a
submersed plant with long slender stems. Hydrilla’s leaves are
small and grow in whorls of 4 to 8 around the stem. Leaves are small,
linear, and pointed with serrate edges. Hydrilla produces small white
flowers on the stalks.
Biology
Hydrilla is capable
of growing in virtually any water body, including lakes, streams,
ponds, and canals. While it generally grows submerged, it often forms
dense mats at the surface which are very detrimental to the ecosystem.
The plant reproduces by stem fragments carried by people or boats.
Seeds and capsules can also disperse through water or be carried by
animals. Due to these highly specialized growth habits, hydrilla has
spread rapidly along the coastal United States.
Hydrilla provides
habitat for black bass and forage fish so sport fishermen appreciate
the plant. However, in high densities the plant can interfere with
navigation. Consequently, it is a challenge to manage this plant in
a way to satisfy all demands.
History
Hydrilla verticillata
is a plant native to the warmer parts of Asia. Hydrilla first appeared
in the United States in Florida in 1960. Since then hydrilla has spread
west as far as California and north as far as Delaware. Due to its
rapid spread throughout the United States, has become a serious problem
weed. The plant is capable of displacing native plants, impacting
water quality, and interfering with various water usages, both economical
and recreational.
Foreign exploration
for insects as biological control agents were conducted by Balciunas
(1982, 1983, 1984, 1985) and Balciunas and Dray (1985). Five candidate
species were investigated in subsequent quarantine studies (Balciunas
1987; Balciunas and Center 1988; and Balciunas, Center, and Dray 1989).
The species that have been released in the U. S. are: hydrilla tuber
weevil, Bagous affinis; and two hydrilla leaf-mining flies,
Hydrellia balciunasi and Hydrellia pakistanae (Buckingham
1990; Center et al. 1991).
Biological Control Agents
Literature
Buckingham, G.
R. 1988. Reunion in Florida – Hydrilla, a weevil, and
a fly. Aquatics 10(1): 19-25, illus.
Balciunas, J.
K. 1982. Overseas searches for insects for control of aquatic plants.
Pages 141-145 in Proceedings, 16th Annual Aquatic Plant
Control Research Program and Operations Review. Miscellaneous Paper
A-82-3. US Army Engineer Waterways Experiment Station. Vicksburg,
MS.
Balciunas, J.
K. 1983. Overseas searches for insects on hydrilla in Southeast Asia
and Australia. Pages 104-114 in Proceedings, 17th Annual
Aquatic Plant Control Research Program and Operations Review. Miscellaneous
Paper A-83-9. US Army Engineer Waterways Experiment Station. Vicksburg,
MS.
Balciunas, J.
K. 1984. Overseas searches of biocontrol agents for hydrilla. Pages
76-84 in Proceedings, 18th Annual Aquatic Plant Control
Research Program and Operations Review. Miscellaneous Paper A-84-4.
US Army Engineer Waterways Experiment Station. Vicksburg, MS.
Balciunas, J.
K. 1985. Final report on overseas surveys (1981-1983) for insects
to control hydrilla. Technical Report A-85-4. US Army Engineer Waterways
Experiment Station. Vicksburg, MS.
Balciunas, J.
K. 1987. Australian insects to control hydrilla. Pages 57-66 in Proceedings,
21th Annual Aquatic Plant Control Research Program and
Operations Review. Miscellaneous Paper A-87-2. US Army Engineer Waterways
Experiment Station. Vicksburg, MS.
Balciunas, J.
K., and F. A. Dray. 1985. The search for insects to control U. S.
hydrilla populations. Pages 75-78 in Proceedings, 19th
Annual Aquatic Plant Control Research Program and Operations Review.
Miscellaneous Paper A-85-4. US Army Engineer Waterways Experiment
Station. Vicksburg, MS.
Balciunas, J.
K., and T. D. Center. 1988. Australian insects to control hydrilla,
an update. Pages 312-319 in Proceedings, 22th Annual Aquatic
Plant Control Research Program and Operations Review. Miscellaneous
Paper A-88-5. US Army Engineer Waterways Experiment Station. Vicksburg,
MS.
Balciunas, J.
K., T. D. Center, and F. A. Dray, Jr. 1989. Testing suitability of
Australian bioagents for control of Hydrilla verticillata. Pages 24-27
in Proceedings, 23th Annual Aquatic Plant Control Research
Program and Operations Review. Miscellaneous Paper A-89-1. US Army
Engineer Waterways Experiment Station. Vicksburg, MS.
Buckingham, G.
R. 1990. Quarantine work – Insect biocontrol for hydrilla. Pages
28-33 in Proceedings, 23th Annual Aquatic Plant Control
Research Program and Operations Review. Miscellaneous Paper A-89-1.
US Army Engineer Waterways Experiment Station. Vicksburg, MS.
Center, T. D.,
F. A. Dray, Jr., and W. C. Durden. 1991. Release and Establishment
of Insect Biocontrol Agents for Hydrilla Control. Waterways Experiment
Station, MP A-91-3.
Westbrook, R.
1998. Invasive plants, changing the landscape of America: Fact book.
Federal Interagency Committee for the Management of Noxious and Exotic
Weeds (FICMNEW), Washington, D. C. 109 pp.
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