Dr. Leonie Richardson

1
Presentation Title
The Great Japanese Knotweed Debate

• Dr. Leonie Richardson
• Science Shops Wales

2
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

3
Identification and Biology

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

4
Identification and Biology

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

5
Growth and Dispersal

• Vigorously competitive tolerant of a wide range
  of conditions (soil type, pH, salinity,
  temperature)
• 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
  plants
• Dispersal occurs primarily via watercourses,
  transport routes, waste land, and human activity
• No natural competitors

6
Problems

• 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

7
Control Methods

• Can be controlled but requires labour,
  persistence and a good understanding of available
  methods
• 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
  1991
• 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

8
Control Methods1. Dig and Dump

• Digging 3 m deep 7m beyond periphery
• Digging can not be carried out within 10 m of a
  watercourse
• 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

9
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
10
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
  required

11
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)

12
Control Methods5. Chemical Treatment

• Main herbicides in UK are Picloram, 2,4-D,
  Glyphosate, Imazapyr and Triclopyr
• Selection based on site location and future
  land-use
• 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
  yrs)

13
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
14
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

15
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
  treatment
• Effects on health and persistence are widely
  disputed

16
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)

17
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
  considered
• Rigorous testing in secure quarantine according
  to international protocols
• Negligible risk to UK species

18
Control Methods6. Biological Control
Stem boring Weevil Lixus sp.
Leaf-spot fungus Microsphaerella sp.

• Sap-sucking plant louse (Psyllid) Alphalara sp.

19
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
  treatment
• Compulsory Digging prior to membrane
  installation
• Dividing the land and using different techniques
  in different areas

20
Control Methods8. Do nothing

• No costs involved
• No chemicals involved
• Knotweed spread will continue unchecked
• Associated problems remain

21
Costs

• 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
  present
• Arbitrary costs based on 1500 m x 8 m 12,000 m2

22
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

23
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

24
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 /
  hour)
• 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

25
Aman Valley CostsGrazing

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

26
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
  324,000
• Quote from EcoControl Solutions, Cardiff for
  12,000 m2 140,000
• Advice from Invasive Plant Company, Manchester
  suggests above figures are realistic

27
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
  effectiveness
• Unable to provide generic evidence-based
  management guidelines
• Study recommends further long-term research,
  monitoring, replication and investigation

28
Presentation Title

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