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Dr. Leonie Richardson


Rhizomes capable of extending up to 7 m and to a depth of 3 m ... Rhizome is broken up to stimulate growth rendering plant more susceptible to ... – PowerPoint PPT presentation

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Title: Dr. Leonie Richardson

Presentation Title
The Great Japanese Knotweed Debate
  • Dr. Leonie Richardson
  • Science Shops Wales

Introductory History
  • Native to East Asia
  • Introduced to UK mid 19th Century as an
    ornamental plant and for fodder
  • International Union for Conservation of Nature
    Top 100 list of invasive species
  • Distinct British female clone, Fallopia japonica
    var. Japonica

Identification and Biology
  • Young shoots appear MarchApril green/red stems
    with red speckles
  • Branching, hollow, bamboo like stems up to 3 m
  • Extends by rhizomes (horizontal underground
    stems) woody with orange-coloured centres

Identification and Biology
  • Oval shaped, smooth edged, alternate leaves (515
  • Many small (3 mm) green / white flowers arranged
    in dense clusters August - October
  • Few seeds produced from hybrid unions low
  • Old growth dies back dormant over winter
  • Dead stems and leaf litter prevent establishment
    of native seeds

Growth and Dispersal
  • Vigorously competitive tolerant of a wide range
    of conditions (soil type, pH, salinity,
  • Rhizomes capable of extending up to 7 m and to a
    depth of 3 m
  • Shoots can grow up to 8 cm/day due to nutrients
    stored in extensive rhizome system
  • Very small fragments (0.7 g) give rise to new
  • Dispersal occurs primarily via watercourses,
    transport routes, waste land, and human activity
  • No natural competitors

  • Damage to paving, tarmac, walls, flood defences,
    archaeological sites
  • Reduction of biodiversity
  • Restriction of access to river banks / footpaths
  • Risk of soil erosion and bank instability
    following removal
  • Increased risk of flooding
  • Aesthetically displeasing

Control Methods
  • Can be controlled but requires labour,
    persistence and a good understanding of available
  • Early identification and action is preferable
  • Infested soil can not be removed from site except
    to landfill license requirements
  • All knotweed and knotweed contaminated soil
    classed as controlled waste under Environmental
    Protection Act (1990) Duty of Care Regulations
  • It is an offence to plant or cause knotweed to
    spread under Wildlife and Countryside Act, 1981
  • 5 k fine and/or 6 months imprisonment

Control Methods1. Dig and Dump
  • Digging 3 m deep 7m beyond periphery
  • Digging can not be carried out within 10 m of a
  • Burning of material prior to burial is permitted
    under an exemption from Schedule 30 of Waste
    Management Regulations 1994
  • Do not burn actively growing plants
  • Required on-site burial depth is 10 m
  • Required land-fill burial depth is 5 m

Control Methods2. Root Barrier Membrane
  • Root barrier membrane may be installed prior to
    engineered surfaces e.g. tarmac / buildings
  • Membrane should be large securely sealed
    durable UV resistant
  • Membrane should be placed 2 m or deeper to
    minimise damage from burrowing animals

Cell formation using the Dendro-Scott root
barrier membrane
Preventing horizontal spread using vertical root
barrier membrane
Control Methods3. Mowing or Pulling
  • Mowing every 4 weeks or more during the growing
    season will slow or halt rhizomes
  • First cut when first shoots appear last cut
    before Autumn die-back
  • Pulled material should be dried and burned /
    buried at the earliest opportunity
  • Labour intensive small areas / young stands only
  • Mowing may encourage spread collecting box

Control Methods4. Grazing
  • Formerly used as stock feed palatable to cattle,
    goats, horses and donkeys
  • Introduce animals early in growing season after
    June, stems may be too woody
  • Later introductions require pre-cutting to
    encourage tender, palatable shoots
  • Limited control, no eradication care and
    containment of livestock land ownership
  • Palatable to humans source of Vitamin A/C,
    potassium, phosphorous, zinc, manganese,
    resveratrol (which lowers cholesterol) and emodin
    (natural laxative)

Control Methods5. Chemical Treatment
  • Main herbicides in UK are Picloram, 2,4-D,
    Glyphosate, Imazapyr and Triclopyr
  • Selection based on site location and future
  • Treatment must be carried out by a qualified
    person under National Proficiency Tests Council
  • Environment Agency approval required if site is
    near a watercourse
  • Techniques Spraying / Injection
  • Herbicides most efficient near flowering stage
  • Avoid treating during flowering stage to protect
    pollinating insects
  • Most are ineffective during winter
  • Chemical treatment usually requires 3 years
  • May force knotweed into dormancy (rhizomes gt 20

Control Methods5.1 Picloram
  • Persistent in soil for up to 2 years
  • Can not be used near water
  • Selective herbicide affecting broad leaved
    species, but has little effect on grasses
  • May be chosen if not replanting or only grass
    sward is to be maintained
  • Can be applied to the soil during winter

Post-treatment reaction to Picloram
Regrowth after Picloram treatment
Control Methods5.2 2,4-D
  • 2,4-Dichlorophenoxyacetic Acid
  • Selective herbicide affecting broad leaved
    species, but has little effect on grasses
  • Approved for use near water
  • Soil persistence up to 1 month
  • Replanting usually possible after 12 months
  • Possible human carcinogen

Control Methods5.3 Glyphosate
  • Tradename formerly Roundup under Monsanto
  • Method of choice for knotweed control in Rhondda
    Cynon Taff County Borough Council
  • Total herbicide harms all green plant tissue
  • Has little or no soil persistence
  • Approved for use on or near watercourses
  • Low toxicity / environmentally safe
  • Replanting usually possible immediately after
  • Effects on health and persistence are widely

Control Methods6. Biological Control
  • Not yet introduced
  • Natural population control
  • Single clone renders plant more susceptible
  • Low costs following initial research phase
  • No threat to human health, crop production or
    beneficial organisms
  • Relatively long time-scale (510 years)

Control Methods6. Biological Control
  • CABI Bioscience and Leicester University 2nd
    phase of research, 4 year programme
  • 3 potential agents identified
  • Only natural, knotweed specific enemies
  • Rigorous testing in secure quarantine according
    to international protocols
  • Negligible risk to UK species

Control Methods6. Biological Control
Stem boring Weevil Lixus sp.
Leaf-spot fungus Microsphaerella sp.
  • Sap-sucking plant louse (Psyllid) Alphalara sp.

Control Methods7. Combined Treatment
  • Combining digging and herbicide spraying may
    reduce time required for herbicide control
  • Pre-treatment digging to 50 cm often advised
    prior to herbicide application
  • Rhizome is broken up to stimulate growth
    rendering plant more susceptible to herbicide
  • Compulsory Digging prior to membrane
  • Dividing the land and using different techniques
    in different areas

Control Methods8. Do nothing
  • No costs involved
  • No chemicals involved
  • Knotweed spread will continue unchecked
  • Associated problems remain

  • Estimated cost of controlling Japanese Knotweed
    in UK is 1.5 bn
  • At the current rate of treatment (2 ha/yr) the
    infestation will take gt50 years without
    accounting for its rapid spread
  • Worst case scenario is a 1 m2 patch costing
    54,000 to eradicate prior to building
  • Aman Valley Greatest concentration of Japanese
    Knotweed is along a 1.5 km stretch of road
    (Foundry View Incline Row), where the plant
    spreads 4 m either side of the road, following
    the river
  • Likely to be additional patches of knotweed
  • Arbitrary costs based on 1500 m x 8 m 12,000 m2

Aman Valley CostsDig and Dump
  • Digger driver 250 / day
  • 5 weeks? 6250
  • Landscaping costs 8 / m2 96,000
  • Excavation 12,000 m2 to 3 m depth 36,000 m3
    72,000 tonnes
  • Landfill tax is 32 / tonne 2,304,000
  • NB. This amount can be reduced
  • Additional costs associated with licensed
    transport / papers
  • Possible landfill tax exemption only until
    December 2008

Aman Valley CostsRoot Barrier Membrane
  • Membrane costs and installation 63 / m2
  • Additional costs associated with landscaping 8
    / m2
  • Total cost for 12,000 m2 852,000
  • NB. Additional costs associated with cutting of
    site prior to membrane installation

Aman Valley CostsPulling / Mowing
  • Studies show that it takes up to 2 h to remove a
    1m2 area
  • Cost for pulling 137,520 (minimum wage 5.73 /
  • Repeated 4 times / year for 3 years 1,650,240
  • Mowing would be quicker and therefore cheaper,
    though additional costs incurred through tractor
    hire / fuel / maintenance
  • Additional costs associated with removal / burial
    of knotweed

Aman Valley CostsGrazing
  • 12,000 m2 3 acres
  • 6 goats per acre 18 goats
  • Cost of goats?
  • Land ownership winter feed nutritional
  • Grazing every year for 3 years
  • Livestock fencing labour 6 / m
  • 3016 m 18,096

Aman Valley CostsChemical Herbicide Control
  • Spraying costs are 1/m2 8/m2 landscaping
  • 12,000 m2 would cost 108,000 / year to treat
    with herbicide
  • Treatment would continue for a minimum of 3 years
  • Quote from EcoControl Solutions, Cardiff for
    12,000 m2 140,000
  • Advice from Invasive Plant Company, Manchester
    suggests above figures are realistic

Treatment Effectiveness
  • Recent investigation into effectiveness of
    Knotweed control by Centre for Evidence-Based
    Conservation (Kabat et al. 2006)
  • 6 techniques assessed Glyphosate and Imazapyr
    used alone / combination cutting alone cutting
    and filling stem with Glyphosate cutting and
    spraying regrowth with Glyphosate
  • No techniques resulted in eradication
  • All showed significant short-term reduction
    except cutting alone
  • Lack of robust evidence for long-term
  • Unable to provide generic evidence-based
    management guidelines
  • Study recommends further long-term research,
    monitoring, replication and investigation

Presentation Title
  • What do you think is the best method of control?
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