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Aquatic Weed Management: Biological and Physical

Aquatic Weed Management: Biological and Physical

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Aquatic Weed Management: Biological and Physical

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  1. Aquatic Weed Management:Biological and Physical Gary Burtle University of Georgia

  2. Aquatic Weed Control • Types of control • Physical – Pond design or weed removal • Chemical - Herbicide • Biological – Grass Carp, beetles, wasps, viruses

  3. Pond Design • Eliminate shallow areas • Survey water line before construction • Reduce water outflow • Build out of channel or divert water • Three sides open to wind • Clear timber inside and out of pond • Trees in pond are substrate for weeds • Minimum 3 feet deep in dry weather

  4. Grass Carp Stocking In Georgia • Use only Triploid Grass Carp • Stock at 5-10 per acre before weeds start to grow • Use 20 to 40 per acre for existing weed problems • Use 50 or more per acre if algae is a problem (copper resistant species) • Use spillway fences

  5. Grass Carp Size at Stocking • For new ponds can use 3-5 inch carp ($2 to $5.00 each) • For ponds with large bass and weed infestations use 1 pound carp ($9.00 to $15.00 each)

  6. One Pound and 14 inches

  7. Limits of Grass Carp • Effective for about 6 years • Large carp do not eat aggressively • Grazing is a slow control method • Heavy grass carp stocking can interfere with bream spawning activity

  8. Grass Carp Feeding • Weed is sucked into the mouth • Must be soft enough to swallow • Teeth are in the throat • Grass carp cannot “bite off” stems

  9. A Comparison  of Fish Populations Before and After Extensive Grass Carp Stocking • Almost no effect upon total standing crop, shad biomass, numbers of catchable largemouth bass, sunfish, and crappie, or numbers of young-of-the-year sunfish and bass. • Improve the condition factor of largemouth bass, bluegill, and redear sunfish.

  10. Lake Conroe Debate • Stocked Grass Carp to remove hydrilla • 1980 to 1983 most hydrilla eaten • 1983 to 1986 increase productivity • 1986 nutrients back to pre-1980 • 1988 to 1993 catch per unit effort increases

  11. Lake Conroe Now • Return of aquatic macrophytes • Bass fishermen seem to like it • Say larger bass are present • Home owners want more grass carp • Access to lake front is degraded • Hydrilla is coming back at the expense of the natives that were planted

  12. What is Real • Macrophytes are reduced in the presence of grass carp • Grass carp have a 5 to 6 year useful life • Release of plant nutrients is short term • Management of pond or lake productivity involves more than macrophyte removal

  13. Short Term GC Effect on Bream • 19 month trial, in ¼ acre ponds • Initial 1,500 bluegill, 100 bass/acre • 52% reduction in bluegill standing crop • No reduction in bass standing crop • What does this mean?

  14. Grass Carp and Pond Fish • Grass carp may disturb bream spawning in shallow ponds • Reduced weeds as cover allows bass predation of bream • Grass carp do not eat a significant amount of fish, if any • Grass carp will eat fish food pellets

  15. Grass Carp • Spillway barriers • 2 inch spacing between bars • Keep debris removed • High enough to prevent overflow

  16. Spillway Barriers

  17. Other biological controls • Usually for large-scale projects • Alligator weed flea beetle, thrips and stem borer • Water hyacinth weevils, moth • Water lettuce weevils, moth • Hydrilla weevils, leaf mining flies, moth

  18. Alligatorweed Flea Beetle • Pre release, 1963, 97,000 acres of problem alligatorweed • 1981, less than 1,000 problem acres of alligatorweed • Source: Dept of Entomology, Texas A&M

  19. Drawdown in Winter • Drop pond water level to expose shallow areas (large pond option) • November, December, January • Do not do this in warm weather • Can apply herbicides to exposed plants • Dichlobenil • Rodeo • Galleon

  20. Resistant to Drawdown • Bladderwort, Hydrilla, Illinois pondweed, Chara, Variable leaf milfoil • Have drought resistant seeds, rhizomes, etc. • Alligatorweed, Arrowhead, Bulrush, Maidencane, Pickerelweed, Smartweed, Spikerush, Water Hyacinth • Marginal or floating plants

  21. Effects of Summer Drawdown

  22. Mechanical removal • Works when: • Pond is small • Start early • On small lake frontage • For boat paths • Does not work when seeds and cuttings spread around pond

  23. Reducing Light Availability • Chemical dyes • Work but also limit fish food organisms • Shade cloth • 50 to 75% shade needed • Fertilization of “bloom” • Pond must be 3-4 feet deep at minimum

  24. Why Use Barriers? • Non-chemical • For small area control • For use in multi-owner lakes • For use in slow moving waters

  25. Some Disadvantages • Placement is difficult unless water is removed from the area • Sediment accumulation must be removed by routine maintenance • Initial cost is considerable • May float, bubble, or tear • Inhibits benthic organisms

  26. Types of barriers • Sand-gravel • Polyethylene • Polypropylene • Synthetic rubber • Burlap • Fiberglass screen • Polyester

  27. Costs • Synthetic woven material • 300’ x 15’ = $350 ($0.07/sq ft) • Burlap • $0.15-$0.25/sq ft • Installation • $0.25 to 0.50/sq ft

  28. AquaScreen • Woven • 7’ x 100’ weighs 34 lb • 15’ x 360’ weighs 250 lb • Weight with sand bags • Seven year lifespan • www.awc-america.com

  29. Divers Installing AquaScreen

  30. Hydrilla Barrier • Synthetic fiber, biodegradable (nursery supply type) • Or black plastic with 1/8” holes every 24” • Anchor with long pieces of rebar laid lengthwise • Hold down with L-shaped hooks • Sandbags slide on steep slopes

  31. Hydrilla in foreground, dock and beach are clear over barrier

  32. Sand and Stone Anchoring

  33. The “Bloom” • Algae, phytoplankton, that shade the pond bottom by absorbing light • Established by using a fertilization program • Not always possible

  34. Low oxygen levels (organic) Use the correct amount of fertilzer Prepare for low oxygen regardless of schedule Costs of either the product (inorganic) or transportation (organic) Greater variation in daily oxygen and pH levels Increased aquatic vegetation Stock grass carp Concerns Related to Fertilization

  35. Integrated Aquatic Plant Management • Identify intended uses and plants that hinder these uses • Understand the plant ecologies • Set management goals • Consider management methods • Develop an Action Plan • Use a long term education program

  36. Conclusion • Combine biological, mechanical, and chemical control • Use only labeled chemicals • Use the Extension tools