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New Hampshire Department of Environmental Services
PUBLIC GOVERNMENT BUSINESS A to Z LIST

Plant Control Techniques
Hand Pulling (physical)
Effectiveness: Removes a few individual plants at time
Specificity to Target: High
Advantages: Good for localized areas/ few plants.
Plants physically removed from waterbody
Disadvantages: Labor intensive Good for small infestations only.
Not practical when plant growth is dense
Cost*: Labor Costs vary depending upon contractor costs or staff time
Mechanical Harvesting (physical)
Effectiveness: Removes large amounts of vegetation at a time
Specificity to Target: Not Specific
Advantages: Rapidly removes vegetation from area
Plants physically removed from waterbody
Disadvantages: Fragments plants which could cause regrowth
Removes beneficial native vegetation.
Could increase turbidity, ultimately affecting other aquatic life
Does not remove rooting systems
Cost*: Ranges widely depending on plant density, location, disposal, etc.
Generally $350-$1500 per acre
Hydro-raking (Physical)
Effectiveness: Removes large amounts of vegetation at a time
Specificity to Target: Not specific
Advantages: Rapidly removes vegetation

Removes rooting systems to prevent rapid regrowth.

Plants removed from waterbody

Disadvantages: Fragments plants

Could increase turbidity, ultimately affecting other aquatic life

Removes beneficial native vegetation

Cost*: Ranges widely depending on plant density, location, disposal.

Generally $350-$2500 per acre

Benthic Barrier permeable non-permeable (Physical)
Effectiveness: Used for very small infestations
Specificity to Target: Specific to area where barrier is located Impacts all plants under barrier
Advantages: Compresses plants to sediments and prevents likelihood of fragmentation by wind, wave, or anthropogenic means
Disadvantages: Labor intensive

Must frequently be cleaned/re-staked

Plants not physically removed from waterbody

May cause sediment/water anoxia

May impact non-target species such as fish, invertebrates, and others

Cost*: $0.60-$1.22 per square foot
or
($25,000-$50,000 per acre)
Chemical Treatment
Effectiveness: Herbicides which are taken up by root systems (systemic herbicides) more effective than contact herbicides
Specificity to Target: Most chemicals have target species for which they are most effective

Varying application rates can increase target specificity

Advantages: Chemical has potential to eliminate exotic plant infestation if done at correct time, and if correct concentration is used

Relatively rapid effect

Longer time span of control than other types of control techniques

Disadvantages: Addition of chemical to waterbody

May impact non-target species if not applied according to label restrictions

Could be environmentally damaging if not applied per label restrictions

Cost*: Varies with chemical and size of treatment area

Could range from $200-$1000 per acre.

Drawdown (Habitat manipulation)
Effectiveness: Somewhat effective if repeated frequently

More effective if drawdown maintained for long time period

Specificity to Target: Not specific
Advantages: Could control density of vegetation due to plant die off from dessication or freezing

Winter drawdowns favorable

Disadvantages: Impacts non-target plants

Impacts fish, amphibians, insects, and other aquatic organisms

Devastating to entire waterbody ecology

Cost*: Low cost if dam or other means of drawing down water is available
Dredging (Habitat manipulation)
Effectiveness: Effective in removing plants from localized area where dredge takes place
Specificity to Target: Not specific
Advantages: Completely removes plant material

Removes nutrient laden sediments

Removes seed bank

Disadvantages: Devastating to entire system.

Impacts non-target plants and animals

Could cause excessive turbidity

Must wait for waterbody to be filled again

Cost*: $16,000-32,000 per acre

Previously used and successful in one lake in New Hampshire (Milville Lake)

Biological Controls
Effectiveness: Effective against target plants
Specificity to Target: Specific
Advantages: Insects, bacteria, or viruses used in this method are typically specific to target plant. Their life cycles revolve around particular plant species

Does not affect other non-target species

Disadvantages: May cause decline in oxygen as plant material decays

Many biological controls are themselves exotic

Still experimental

Cost*: Cost of insects

Monitoring cost high

* Costs are averages determined from data obtained from "Draft Generic Environmental Impact Report" for Massachusetts, and from Aquatic Control Technology, Inc. Fact Sheet.




NH Department of Environmental Services | 29 Hazen Drive | PO Box 95 | Concord, NH 03302-0095
(603) 271-3503 | TDD Access: Relay NH 1-800-735-2964 | Hours: M-F, 8am-4pm

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