Japanese Knotweed Management and Remediation

Transcription

1 Japanese Knotweed Management and Remediation

2 JAPANESE KNOTWEED - OVERVIEW

3 JAPANESE KNOTWEED - OVERVIEW o a large, herbaceous perennial plant, native to eastern Asia in Japan, China and Korea. o first introduced to Britain by the Victorians as an ornamental plant - and was actually awarded a gold medal at a prestigious flower show. o Wildlife and Countryside Act Listed under Schedule 9, Section 14 of the Act, it is an offence to plant or otherwise cause the species to grow in the wild.

4 Why is it so bad? o Perennial and extremely invasive. It thrives on disturbance. o Native environment comprises of harsh infertile soil. o Aggressive growth rate. o No natural predators. o Control and eradication can take up funds within a project or increase timescales for completion.

5 Why is it not so bad? o Fixed location; o Does not spread aggressively without human interaction; o Can reduce cost of buying land; o Multiple methods of control solution; o Will grow where it is easiest to grow does not grow through concrete / floors for fun; o Is NOT the end of the world.

6 Interesting Knotweed facts o Flowers are a valuable resource of nectar for bees; o Early shoots are edible tastes like rhubarb; o Has herbal applications contains high levels of resveratrol (a phytoalexin antibiotic for plant defence system) and emodine (a mild laxative); o The rhizome can produce a yellow dye; o The plant can adapt to any form of soil type regardless of conditions. o Almost every plant outside Japan is derived from the same mother plant. In total biomass terms, this clone is probably the biggest female in the world.

7 IDENTIFYING JAPANESE KNOTWEED Growing season begins in at the end of March and closes at the end of October in general this is dependant of the climate during the year.

8 When is Knotweed Identified Infestations of Japanese Knotweed should be picked up during the following surveys: o Phase 1 Environmental Desk Study o Ecological Walkover protected species survey, biodiversity survey, etc. For suspected infestations you should not be paying for a specialist to visit site reports are a waste of money as well.

9 Early stages March onwards o Red bulbs form that progress to - o Red / green vertical shoots. o Can be thick like asparagus or thin. o Plant achieving height over lateral extent. o Predation will result in bonsai growth. o These can occur throughout the growing season.

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14 Growing and Mature Plants - May onwards. o Plants can extend in excess of 3m. o Red speckled stems (sometimes not). o Distinctive spade shaped leaves in defined pattern. o Hollow stems, easy to break. o Stems split into a series of nodes. o Small white flowers appear late summer.

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19 Winter Evidence o Plants die at the growing season rhizome still active. o Canes are a visible remnant brown / deep red. o Easily broken. o Can be confused with other plants easily, scale and features are a give away.

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23 Rhizome systems o Very difficult to differentiate between rhizomes in similar plant. o Dark brown exterior. o Orange / white in colour within interior. o Snaps rather than tears. o New roots are white. o Does not smell.

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26 ONCE JAPANESE KNOTWEED IS IDENTIFIED. Once Japanese Knotweed is positively identified on a site, the following should be assessed: o Where is the knotweed? o What type of infestation is it? o What is the risk to the site? o Why is it there?

27 Knotweed Location o Boundaries of site? Interior of the site? o Next to buildings? Under structures / concrete? o Within stockpiles? The location of knotweed will help identify the following: o Why it is where it is. o Indication of cost / timescale. o Indication of overall risk / difficulty to eradicate.

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34 Type of growth o Knotweed is only spread through soil disturbance but the rhizome system will extend with time. o Identify if the knotweed is an established system or a pocket of aggravated growth. o Assess the location and characteristics of the plant.

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38 What is the risk? o Proposed Development? o Difficult location? o Off-site impact? o Widespread or localised? o Timescales? o IMPORTANTLY what will happen if eradication is not successful?

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40 Why is it there? o Demolition? o Fly tipping? o Migration from adjacent site? o Stockpiled materials? These questions provide data to begin a site specific approach to management.

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45 I have Japanese Knotweed on my Site! o Assess the cost implications; o Assess the time implications; o Assess the residual risk to the site; o Determine method of control; o Select a Contractor;

46 Cost and Time Implications o Knotweed eradication programs are either time consuming or can be expensive. o Quickest solution, to remove off site, often costs the most. o Cheapest option often takes the longest. o Realistic budget considerations. o If development is not to take place, longer term solutions are better.

47 Assessing residual risk o Plant movement through infested areas; o Proposed development; o Large quantities of soil movement; o Time of year; o Herbicide treatment does not remove roots; o Adjacent off site?

48 METHODS OF CONTROL AND UNDERTAKING WORKS

49 Methods of Control o Herbicidal Treatment; o Ex situ removal; o Burial; o Root Barrier Membranes o Process removal; o Combined methodology approach.

50 Herbicide Treatment o Can take many growing seasons to complete; o Does not remove rhizome material; o Inexpensive; o Restricted by local environment; o Various herbicides available (glyphosate or picloram); o Plants can adapt if not fully killed; o Can blight the soil; o Injection preferable over spraying; o Cheapest option.

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54 Ex-situ removal (Dig and Dump) o Quickest solution; o Can promote spread of knotweed; o Must be properly managed; o Waste must be removed as controlled o Costs dependant on lab analysis; o Can be expensive if reduced volume removal not undertaken; o Success dependant on contractor skill / experience; o Duty of care must be in place; o Time of year when undertaken.

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57 Process Removal o Soils excavated and processed to either kill or remove rhizome material from site won soil then reused. o Expensive to undertake; o Same risks as ex situ removal; o High risk approach rhizome extremely difficult to remove or kill; o Dependent on geology and hydrology;

58 Burial of rhizome material o As per dig and dump but soils buried onsite within a cell defined by a root barrier membrane. o Same risks as ex situ removal; o Scale of burial often restrictive; o Dependent on geology and hydrology;

59 Root Barrier Membranes o Only used in specific situations; o Can be vertical or horizontal; o Typically to segregate the site from an adjacent infestation; o Must be installed correctly; o Is area of site to be developed and puncture membrane? o Inexpensive; o Difficult to tie-into development scheme affixing to fences, etc.

60 Combined Methodology o Common approach; o Site specific approach and balances cost / time implications; o Typically ex-situ removal and herbicidal treatment; o E.g. Ex situ removal on site, root barrier membrane installed along boundary and herbicide treatment on adjacent land.

61 The Psyllid, Aphalara itadori o Biological control within the UK as introduced species; o First time approved within the European Union; o Advice was sought within the industry in an open consultation; o Tests undertaken on knotweed and 90 other similar plant types; o All those that fed on other plants did not develop into adults o Is a parasite parasites tend not to kill the host. o Inexact control at best.

62 Undertaking works - There is Knotweed on an adjacent site o How close is it? o Inform the owners; o Factor into type of control and eradication; o Be co-operative and constructive; o Most developers pay for some kind of herbicidal treatment to adjacent sites to mitigate residual risk; o Do not alarm to neighbour this creates problems.

63 Knotweed Management Plans o Determined by the EA Code of Practice o Serves as a proposed plan of works, record of works undertaken and overall objectives to be achieved; o Serves as duty of care; o Contains records of herbicide treatments; o Serves as validation document, verification and closeout report;

64 Selecting a Contractor o Will they visit the site for free prior to quoting? o Have they quoted for a Knotweed Management Plan? o Acceptable methodology proposed? o Correct herbicides used? o As part of a bulk scheme of works or separate contractor? o Understand the potential risks of undertaking works? o Have access to the proposed development and site history and are able to make judgements about the source of infestations.

65 What to watch out for o Too good to be true herbicidal treatment claims! o Warranties that are unacceptable; o Term and conditions of quotation; o Charges for reports that are not required; o Guarantees that are a false economy. o Does the contractor understand the risks posed by what they are proposing to undertake? o E.g. 3k for one year treatment with 10 year guarantee. Equates to 3 years at 1k per day!

66 Any Questions?