Hydrilla verticillata The fight for control

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Hydrilla verticillataThe fight for control

• Carey Minteer
• Department of Biological Sciences
• University of Arkansas

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Methods

• Mechanical
• Chemical
• Biological

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Mechanical

• Can be used for smaller populations
• Clear boat ways
• Obvious problems

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Chemical

• Flouridone- only chemical approved by the USEPA.
• Inhibits the phytoene desaturase (PDS) enzyme
• Rate limiting enzyme in carotenoid biosynthesis

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Effects

• Causes photobleaching of green tissues (Böger and
  Sandman, 1998)
• H. verticillata is controlled in large bodies of
  water by sustaining a concentration of 4-12 µg/L
  for several weeks

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Problems

• Expensive
• Hard to maintain proper concentration for proper
  amount of time
• Resistance

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Resistance

• It is considered unlikely in higher plants that
  resistance can occur in the absence of sexual
  reproduction (Hill, 1982).
• However, three biotypes of resistant H.
  verticillata have been found (Michel et. al,
  2004).

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BiologicalThe Fungus and the Fly

• Mycoleptodiscus terrestris (Gerd.) Ostazeki
• Hydrellia pakistanae Deonier

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The Fungus

• Mycoleptodisus terrestris (Gerd.) Ostazeski
• Collected from hydrilla growing in Lake Houston,
  TX in 1987 (Joye, 1990 and Shearer, 1996)
• Currently undergoing evaluation

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Effects

• Fungus can greatly reduce hydrilla biomass.
• After inoculation disease symptoms appear in 5-7
  days.
• Interveinal chlorosis is followed by a complete
  loss of color.
• Plants begin to disintegrate within 10-14 days.
  (Shearer, 1996)

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The Fly

• Hydrellia pakistanae Doenier- Asian hydrilla leaf
  mining fly
• First released in the US on Lake Patrick, FL in
  1987 (Buckingham et al, 1989)
• 750,000 larvae have been released in Lake
  Ouachita.
• 250,000 larvae have been released in Degray lake.

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Biology

• Small, about 2 mm in length.
• Live almost exclusively on or near H.
  verticillata infestations.
• Not strong flyers and appear to hop along the
  water surface (Deonier, 1971)
• Eggs are laid on H. verticillata
• Females lay eggs one at a time, but can produce
  several hundred eggs during her reproductive
  period (Buckingham et al, 1989)

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Biology

• Eggs hatch in 3-4 days depending on temperature.
• Larvae tunnel or mine hydrilla leaves, where they
  feed and destroy 9-12 leaves during the three
  larval stages.
• Total development takes 20-35 days (Buckingham et
  al, 1989)

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Effects

• Reduction in leaf area
• Reduces photosynthetic area and therfore reduces
  vigor and competitiveness (Doyle et al, 2002)
• Damage to canopy leaves approached 100 when
  infested with 4000 larva per m2 (Wheeler and
  Center, 2001)

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Effects

• Under field conditions 20 leaf damage was shown
  when larval levels reached 2320 larvae per kg of
  Hydrilla tissue (Grodwitz et al, 1997).
• 50-75 surface canopy leaf damage when immature
  fly levels were greater than 6000 immature flies
  per kg of H. verticillata.
• Leads to a 30 reduction in biomass, relative to
  controls.
• 15-40 damage with 2000-4000 immature flies per
  kg (Doyle et al, 2002)

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Problems

• Parasitic wasp, Trichopria columbiana, which
  could keep H. pakistanae from establishing.
• Field populations have rarely achieved the
  densities necessary to produce extensive damage
  to H. verticillata.
• Biocontrol agents are unlikely to eradicate
  invasive pests.
• Biological control agents reduce plant vigor and
  competitiveness, rather than cause direct
  mortality (Crawley, 1989)

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Literature Cited

• Böger, P. and G. Sandman.1998 Carotenoid
  biosynthesis inhibitor herbicides- mode of
  action and resistance mechanisms. Pesticide
  Outlook, 929-35.
• Crawley,M.J.,1989. Insect herbiours and plant
  population dynamics. Annual Review. Entomol.
  34531-564.
• Doyle,R.D., M.J. Grodowitz, R.M. Smart, and C.
  Owens. 2002. Impact of herbivory byHydrellia
  pakistanae on growth and photosynthetic
  potential of Hydrilla verticillata.
• Grodowitz,M.J., T.D. Center, A.F. Confrancesco,
  J.E. Freeman. 1997. Release and establishment of
  Hydrellia pakistanea for the biological control
  of the submersed aquatic plant Hydrilla
  verticillata in the United States. Bio. Control.
  915-23.
• Hill, RJ. 1982. Taxonomy and biological
  considerations of herbicide- resistant and
  herbicide-tolerant biotypes. In Herbicide
  resistance in Plants. Pp 81-98. Wiley and Sons,
  Inc., New York, NY
• Joye, G.F. 1990. Biocontrol of Hydrilla
  verticillata with the endemic fungus
  Macrophomina phaseolina. Plant Disease
  741035-1036.
• Shearer,J.F. 1996. Field and laboratory studies
  of the fungus Mycolptodiscus terrestris as a
  potential agent for management of the submersed
  aquatic macrophyte Hydrilla erticillata.
  Technical reportA-96-3. U.S. Army Engineer
  Waterways Experiment Station. Vicksburg, MS.