Untangling the knot - Japanese Knotweed Removal by Environet

GNVH pages 51-66
10/3/09
10:51 am
Page 64
IMAGE: courtesy Musketeers Group
Untangling the knot
Japanese knotweed, first introduced into the UK as an ornamental plant, now plagues the environment and its removal can be costly
and time consuming. However, recent research into biocontrols by scientists at CABI have suggested that a sap-sucking psyllid insect
(Aphalara itadori) could successfully bring Japanese knotweed under control. The news has received a very mixed response from
those involved in the eradication and control of this most pernicious weed. sustain’ invited representatives from three leading
knotweed specialists to debate the issue: MAXIME JAY, Managing Director, Musketeers Group, CLIFFORD HARRIS, Director,
Herpetosure, and NIC SEAL, Director of Environet Consulting.
MUSKETEERS: Why do you feel so strongly against
using bio-control agents for the remediation of
Japanese knotweed? Surely you must see some
benefits from releasing bio-control agents?
HERPETOSURE: I am very cautious about making
further changes to the UK, as the introduction of
non-native species is the problem in the first place.
Developers typically need to eradicate infestations –
not just keep under control – so the bio-controls will
not, in many cases, be the right solution. I am
concerned that the introduction of further species
will potentially harm conservation in the long term if
the new species act differently as predicted.
ENVIRONET: We have concerns about the release of
other non-native species and are yet to be convinced
that this can be done safely without detriment to
other species within our environment. We accept the
excellent research being carried out by CABI and
agree that bio-control agents may control knotweed
– however Environet’s objective, particularly within a
development-site scenario, is eradication which will
PAGE 64 SUSTAIN’ v10 i01
not be achieved with bio-controls. Furthermore, if
Aphalara itadori, or indeed any other non-native
biological control agent, is released into the
environment, how can we be sure that it will only
feed off Japanese knotweed, and not any other
species of perhaps more commercial value, such as
crops, or biological value such as rare flora?
MUSKETEERS: There will always be risks associated
with the introduction of foreign species into a new
environment. We cannot afford to be complacent
about those risks and thus we ought initially to
invest in science. This is in order to understand and
evaluate those risks, providing mitigation measures
to palliate them so that we are able to take
appropriate decisions. With regard to the works
undertaken by CABI, two knotweed predators were
selected out of 226 insects and fungi. The psyllid
and the leaf mould were the only tested predators
that did not attack other plant species. However, the
predators were presented with only 79 different
plants. Although we are not experts in this specific
scientific area, we feel that 79 plants is not a
representative sample of our natural botanic heritage
and consequently further research is required before
a foreign predator is released in the UK.
HERPETOSURE: The new bio-controls may eat
away at the plants, but do they fully eradicate the
plants? If some of the plant is left insitu, the plant
will be viable in the future and therefore surely the
plant will still need to be properly removed later on?
MUSKETEERS: The introduction of a knotweed
predator and consequently the works undertaken by
CABI has never been about Japanese knotweed
‘eradication’ (otherwise the knotweed would have
disappeared from Japan a long time ago!!) but rather
Japanese knotweed ‘control’. The predator will only
attack the visible part of the knotweed thus
weakening, but not killing, the rhizomes. Sites
earmarked for development and contaminated with
Japanese knotweed will still require to be adequately
remediated even if the knotweed has already been
affected by predators. It is not developers that will
benefit from the successful introduction of predators
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but rather large landowners and conservationists
alike. The anticipated outcome should be a slow
down in the spread of Japanese knotweed.
ENVIRONET: Aphalara itadori may control knotweed
but will not eradicate it. It is unlikely therefore to be
the solution for knotweed-infested development
sites, especially with tight construction programmes.
In non-time critical situations it may provide an
element of control, as would a relatively inexpensive
herbicide-treatment programme. Do you not think
that the environmental risks of introducing another
non-native species to control one already causing
havoc in the UK outweigh the benefits, especially as
alternative herbicidal methods can be used
effectively and safely?
MUSKETEERS: Well, let’s examine the facts. The
most cost-effective technique to eradicate Japanese
knotweed is a herbicide-treatment programme.
DEFRA has estimated that the cost of dealing with
knotweed by spraying it would be around £1.5bn. In
addition, it was calculated using a Glyphosate-based
herbicide, which is considerably cheaper than the
more effective but expensive herbicides. We should
consequently expect the real cost of the eradication
of the knotweed to exceed well over the £1.5bn mark.
Even if we kept to a £1.5bn budget, who is going
to pay for this? It is obviously economically impossible
to achieve. Dramatic situations require drastic actions
and the insects would enable the control of the
knotweed without any cost implications.
Moreover, whilst it may be appropriate to spray the
knotweed in a few localised areas, we just do not
know what the impact could be for releasing herbicides
into the environment on a large/national scale.
IMAGE: courtesy Environet Consulting Ltd
PAGE 66 SUSTAIN’ v10 i01
Although far from being ideal, the introduction of
new species into our ecological heritage could
represent an attractive economical option for the
control of Japanese knotweed.
Since you disapprove of the use of bio-control
agents, what would you consider to be the most
cost-effective and practical approach for eradicating
Japanese knotweed?
ENVIRONET: For development sites with tight
programmes we advocate Environet’s Xtraction
method, whereby knotweed rhizome can be
removed from infested soil at a fraction of the cost
of ‘dig and dump’ without the use of any herbicide.
For non development sites, we accept that biocontrol may be appropriate, if, and only if, it can be
done without undue risk to other species within the
local environment.
HERPETOSURE: What about a systematic approach
of mass publicity to enable proper identification,
followed by a county by county eradication
programme? This would be long term, but more
realistic, as we have the means to eradicate
Japanese knotweed available today. Much knotweed
is spread by human beings, so if we can put in place
the right controls to prevent the spread of knotweed
by people, increase identification, and put in place
effective eradication strategies, we could take control
of this problem starting today
MUSKETEERS: Without the introduction of biocontrol agents, how do you see the state of
Japanese knotweed spread (along with its
economic/environment impact) across the UK within
the next 15 years?
ENVIRONET: Despite the efforts of many
organisations tackling the knotweed problem, we
believe it’s growing faster than it’s being killed. With
the current economic situation, less money is likely
to be spent on knotweed treatment over the coming
years so we’re sure the problem is only going to get
worse. But just because the UK has a large and
growing knotweed problem we caution against what
might seem like a cheap solution – the full effect of
bio-control agents will only become apparent after
release – let’s hope we don’t then need to start
looking for another bio-control agent to control the
one for knotweed.
HERPETOSURE: I feel that organisation and
commitment is the key to long-term success. If a
Nationwide programme was developed, invasive
weeds could be attacked in a methodical, coordinated manner and within ten years real results
could be achieved. I am very in favour of new
innovations, but I feel we should focus on utilising
the assets we have.
ENVIRONET CONSULTING LTD
tel: 01932 868700
www.environet-uk.co.uk
HERPETOSURE INVASIVE SOLUTIONS LTD
tel: 01664 444 660
www.herpetosure.com
MUSKETEERS GROUP LTD
tel: 01475 745390
www.musketeers-group.com