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Invasive plants in wetlands and their control . Neil Anderson University of Minnesota Early detection & rapid response. Early Detection: Surveillance Monitoring Control: Rapid response Goal: Prevent new introductions. Early detection: Assessment—vegetation surveys.

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invasive plants in wetlands and their control

Invasive plants in wetlandsand their control

Neil Anderson

University of Minnesota

early detection rapid response
Early detection & rapid response
  • Early Detection:
  • Surveillance
  • Monitoring
  • Control:
  • Rapid response
  • Goal: Prevent new introductions
early detection assessment vegetation surveys
Early detection:Assessment—vegetation surveys
  • Used for:
  • Monitoring for potential invasives
  • Assess effectiveness of vegetation management techniques used
  • Document rare/endangered species
  • Methods:
  • Garmin hand-held units (above-water)
  • Under-water technologies (Trimble units)
  • Cameras,
  • Geographic positioning system or GPS mapping with ESRI ArcGIS software
  • Positive plant identification

water quality surveys
Water quality surveys
  • One-time vs. scheduled monitoring
  • Types: in-lake, storm water, tributary sampling
  • On-site measurements: temperature, dissolved oxygen, water quality
  • Analysis laboratory: pH, total alkalinity, N/P series, turbidity, color, bacteria

bathymetric surveys
Bathymetric surveys
  • Map of water depths
  • Necessary for determining type(s) of control methods
  • e.g. for a drawdown – bathymetry map will calculate water volume and exposed area during drawdown
  • For chemical treatment: accurate water depths, volumetric data to calculate herbicide application amounts

wildlife habitat surveys
Wildlife habitat surveys
  • May be needed for permitting compliance
  • Regulatory agencies
control methods
Control Methods
  • Mechanical
  • Physical
  • Biological
  • Chemical
  • Site Modification
  • Disturbance Regime
  • Ecological Controls
  • Prevention
  • Education

Risky Business: Invasive species management on National Forests A review and summary of needed changes in current plans, policies and programs


mechanical methods
Mechanical methods
  • Hand-pulling
  • Special tools may be required, e.g. Weed Wrench (New Tribe, 5517 Riverbanks Rd., Grants Pass, OR 97527)
  • Use the best tool(s) for the species
hand pulling by divers
Hand pulling by divers
  • Used when plant density is low or intermixed invasive and desirable species
  • May be used with mechanical harvesting, if water edges are not deep enough for diving
effectiveness of hand pulling myriophyllum
Effectiveness of hand pullingMyriophyllum
  • 3-year study
  • While numbers of plants pulled were 3x greater each year, milfoil reproduction was exponential (10x greater/yr)


mechanical cutting harvesting
Mechanicalcutting, harvesting
  • Effective for "area selective" control of invasive aquatics: clearing or cutting through large populations
  • May enhance access for boating, fishing, swimming
  • Works for all plant species, but best for those with a dense surface canopy or those annuals with high seed production (Trapa, water chestnut).
  • Disadvantages?
mechanical raking hydro raking
Mechanical raking,Hydro raking
  • A floating barge with a ‘backhoe’, rake
  • Effective technique for selective removal of rooted vegetation
  • Can clear debris, e.g. muck, peat, decaying leaves
  • Hydraulic paddle wheel for propulsion
  • Can operate in water 0.3 m to ~4 m depths
  • Duration of control ranges for 1 season (Myriophyllum) to 2+ yrs or longer for deep rooted plants (Typha, Nelumbo)
dredging sediment excavation
Dredging(sediment excavation)
  • May provide years of benefit, if done correctly
  • Costly!
  • Significant ecosystem disturbances
  • Requires careful articulation of purpose
  • Sufficient deepening of area needed to preclude light requirements of rooted plants
  • Excavation should not expose inorganic substrates that prevent plant recolonization
physical methods
Physical methods
  • Hot water / steam treatment (“wet infra-red”)*
  • Removes waxy cuticles, causing quick death
  • Not plant specific
  • Enhanced with a surfactant
  • Temporary decrease for ~1 month

*Waipuna Int’l., Carrboro, N. Carolina, USA

fountains and aeration systems
Fountains and Aeration systems
  • Aeration, circulation of stagnant water
  • Suppresses algae
  • Enhance oxygen levels for fisheries
weed barriers
Weed barriers
  • Permeable or ‘Benthic’ barriers secured to lake bottom
  • Eliminates rooted plant growth
  • Effective, ~low cost weed control strategy for small beachfront areas
  • Lowering water levels
  • Requires water control structures to drop water levels for extended time periods
  • In winter, lowering the water level exposes the sediment to freezing, water loss
  • Best for species with no overwintering structures
  • Negative consequences?
chemical methods
Chemical methods
  • Herbicides
  • Broadleaf, grass
  • Selective, non-selective
  • Modes of action: inhibition of electron transport, growth regulation (auxin, cytokinin mimicry), amino acid synthesis inhibition, lipid synthesis inhibition, seedling growth inhibition, photosynthesis inhibition, cell membrane disruption, and pigment inhibition (Anderson, 1994)
  • General in specificity, side effects, application issues
  • Hazards
surfactants wetting agents
Surfactants, Wetting Agents
  • Primarily used as adjuvants with herbicides
  • Increase effectiveness of hot water treatments
  • May control weeds directly
  • (Havey, 1999).
biological controls
Biological controls
  • Seed bank control (Quarles, 1999, Luken, 1990, Luken, 1997)
  • Invasives often dominate seed banks
  • Factors affecting seed bank quantity, viability, quality:
  • (1) Local vegetation sources
  • (2) Seed germination rates
  • (3) Seed decay rate, physical destruction of seeds
  • (4) Seed predation
  • (5) Reseeding efforts
invertebrate biological controls
Invertebrate biological controls
  • Research and release of agents carries the risk that unintended hosts will be attacked and decimated
  • Not every native plant and growing environment can be tested.  Examples:
  • Natural insect enemies (Hobbs and Humphries, 1995)
  • Introduced invertebrate control species
  • Flea beetles (Aphthona spp.) reduces leafy spurge (Euphorbia esula)
  • Galerucella beetles control some populations of purple loosestrife (Lythrum salicaria)
  • Musk thistle (Carduus nutans) control with the head weevil, Rhinocyllus conicus
  • Genetically altered (transgenic or designer) insects may eventually be introduced for weed control
herbaceous fish insects
Herbaceous fish, insects
  • Herbaceous fish: control of nuisance plants, algae
  • Triploid (sterile) grass carp (nonselective)
  • Require permitting
  • Limited to ponds, small lakes where outflow can be blocked
  • Herbaceous insects: control invasive, submerged or emergent aquatic plants
  • Milfoil weevil (Euhrychiopsis lecontei)
  • Purple loosestrife beetle (Galerucella sp)
  • Mixed success
biocontrol disadvantages
Biocontrol disadvantages
  • Not risk-free, e.g., unanticipated host switching
  • Won’t establish or control target pest
  • Establishes but does not increase or spread on its own
  • Successful only 16-26% of the time
pond dyes
Pond dyes
  • Blue, black dyes
  • Alter sunlight penetration into a lake or pond
  • Reduces photosynthetic capacity of plants, algae
  • Not recommended for “natural” ponds
  • More suitable for contained, man-made ponds with little or no outflow (storm water detention ponds, reflecting pond, golf course pond, etc)
  • Break down over time
  • Periodic reapplication
  • Production of plant growth, germination inhibitors by plants (Aldrich, 1987; Harrison and Peterson, 1991)
  • Multiple benefits (Schmidt, 1980; Jarvis et. al., 1985)
  • Controlled allelopathy: possible through planting of allelopathic plants, application of allelopathic chemcals or genetically modifying a plant to produce allelopathic substances
genetic methods
Genetic methods
  • Hybridization - Invading species may evolve or adapt to a less (or more) pathogenic form over time
  • Well-adapted invading species are less lethal to their host ecosystem, e.g., a parasite that kills its host ecosystem is not likely to be successful
  • This effect represents an interaction between the newly invaded ecosystem as well as within the invading organism
  • Biologically engineered hybrids - Genetic engineering has the potential to change the fitness of invading species: lethal mutations, sterility
soil chemistry
Soil chemistry
  • Nutrient availability and cycling to manage invasives: tend to be less dependent on specific soil nutrients
  • Soil pH - high or low soil pH depending on species, e.g., blueberries and other Ericaceous species are acid-loving, whereas species such as some bluegrasses, junipers, etc. favor basic soils
  • Soil amendments can favor desirable species, affecting vegetation dominance
  • Timing of fertilization encourages certain species (Deal, 1966)
  • Amount, timing of shade
  • Duration
  • Impact
  • Effective vegetation management tool (Elmore, 1993b).
  • Straw mulch (6-8cm): 98% control of yellow star-thistle (Centaurea solstitialis) (Dremann 1996)
  • Other types:
  • Greenwaste materials, cover crops (Elmore, 1996; Weston, 1996)
  • Allelopathic mulching (Putnam and Weston, 1986; Altieri and Doll. 1978; Quarles, 1999).
prevention the most important tool
Prevention—the most important tool
  • Prioritize new invaders
  • Use signage along infested areas to avoid public transport
  • Seed transport: a primary cause of the spread of invaders. Prevented by
  • 1. Contaminated seeding mixtures (Quarles 1999); use only 100% noxious-weed free seed
  • 2. Avoid contaminated mulch
  • 3. Avoid contaminated topsoil (Quarles, 1999)
  • 4. Use quarantines and vehicle washing, e.g., of tractors, cattle and logging trucks that may have just passed through a weed-infested site and are planning to go to a new site
  • Eliminate the cause, not the symptoms, of the spread of invaders
  • A. Make a list of targeted user groups
  • B. Provide weed identification information distribution at central locations
  • C. Post public relations / media / local displays at central locations
  • D. Establish a weed sighting report form
  • E. Sponsor research projects that study invasive species (Morrison, 1997). Projects should include a set of study goals; replicate sampling; randomization; controls; preliminary sampling; and sampling authentication. Projects might include setting thresholds for measurement; coherent problem questions; area division; appropriate sample sizes; data distribution tests.
can invasive species be 100 controlled eliminated
Can invasive species be 100% controlled (eliminated)?
  • ~Yes! Early detection / rapid response
  • Mechanical control, e.g. hand-picking of snails and hand-pulling of weeds
  • Chemical control, e.g. using toxic baits against vertebrates and spraying insecticides against insect pests
  • Biopesticides, e.g. Bacillus thuringiensis (BT) sprayed against insect pests;sterile male releases, usually combined with chemical control
  • Habitat management, e.g. grazing and prescribed burning;hunting of invasive vertebrates.
  • No! Phalaris arundinacea—virtually impossible

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