CONTROLLING
INVASIVE PLANTS
IN THE
TWEED CATCHMENT
THE TWEED INVASIVES PROJECT
CONTENTS
1
INTRODUCTION
2
JAPANESE KNOTWEED
4
GIANT HOGWEED
6
HOW TO PREVENT THE
SPREAD OF INVASIVE PLANTS
7
NON-CHEMICAL CONTROL
8
CHEMICAL CONTROL
10
POST CONTROL ACTION
10
HEALTH AND SAFETY
REMINDER
11
OTHER INVASIVES
12
THE TWEED INVASIVES
PARTNERSHIP
13
FURTHER INFORMATION
Acknowledgments
Layout, format and material based on the Environment
Agency’s “Guidance for the control of invasive plants near
watercourses” leaflet. 1996. Thanks to Caroline Drewett –
Medway Invasives, Max Wade – Ecoscope, Lois Child –
Loughborough University and James MacFarlane –
Cornwall Japanese Knotweed Forum.
Photographs supplied by:
Loughborough University
Cornwall Knotweed Forum
Kent County Council
Tweed Forum
INTRODUCTION
Foreign plants have been present in the Tweed catchment
since the 19th century when they were introduced through
botanical garden collections or via accidental importation
with other goods. Many introduced plant species did not
cope well in the climate of Northern Britain, however a few
did and have gone on to aggressively colonise areas of
the Tweed. In the absence of natural predators invasive
species grow unchecked in their new environment and are
able to out-compete native plant species, disturbing the
natural ecology of the area and in some cases posing a
threat to human health and river flooding. The two most
serious and widely distributed invasive plant species in the
Tweed catchment are Giant Hogweed and Japanese
Knotweed, which are commonly found along
watercourses, hedgerows and road verges.
Invasive species are primarily a problem because they:
• Grow extremely densely and shade out native plants
• Provide poor habitat for insects, fish, birds and
mammals
• Increase the risk of river bank erosion when they die
back in the autumn
• Can create a potential flood risk if dead stems fall into
and clog up watercourses
Additionally:
• Giant Hogweed poses a very serious threat to human
health as the leaves and stem contain a poisonous sap.
• Japanese Knotweed has a very aggressive root system
that can cause extensive damage to paths, walls, pipes
and houses.
This leaflet gives general guidance on how to control
Giant Hogweed and Japanese Knotweed and applies to a
range of habitats including gardens, recreational areas and
farmland; however additional care should be taken when
attempting to control invasives near water courses,
wetlands, on river banks or roadsides. A license is required
from SEPA or the Environment Agency if spraying is to be
carried out near water (see below). If you are in any doubt
contact the Tweed Invasives Officer.
1
JAPANESE KNOTWEED
Fallopia Japonica
Ecology
As the name suggests Japanese Knotweed is native to
Asia and was introduced to Britain in the 19th century as an
ornamental plant. Once introduced the plant’s fast, tall
growth, densely packed stems and thick rhizome root
system meant that it quickly started to out compete our
native flora. It is most commonly found along river banks
woodlands, grasslands and coastal areas; however it will
grow just about anywhere, even through walls, concrete
and tarmac.
Japanese Knotweed sprouts in early spring producing
succulent red-stemmed shoots which will grow quickly to
reach a height of up to 1.5m (4-5 feet) by May and as tall
as 3m (9-10 feet) by late summer. In late summer cream
coloured flowers are produced but these produce sterile
seeds in Britain. The leaves die back after the first heavy
frost in autumn, leaving the tall, hollow, tan coloured
stems standing over winter. The fallen stems and leaves,
which breakdown very slowly, quickly form a thick mat
covering the ground, preventing native plant seeds
reaching the ground and germinating. Japanese
Knotweed has an extensive rhizome root network that can
stretch out up to 7m (23 feet) from the edge of the plants
and over 2m (6 feet) deep and it is from these very hardy
roots that new shoots come up each year. The rhizome
root system is very hard to kill and even when physically
removed from the ground sections as small as 1cm (1/2
inch) can re-grow to form a new plant.
It is very easy to miss Japanese Knotweed at first, as it can
look like many other plants, especially in its earliest growth
phases. Experience in England and Wales has resulted in
Japanese Knotweed being given the title of the most
invasive plant in Britain, it is therefore vital that it is
prevented from getting more firmly established in the
Tweed catchment.
2
Identification
Spring
• Red, succulent shoots appear early
Summer/Autumn
• The stems are green with red flecks and can
grow up to 3m (9-10 feet)
• Heart-shaped leaves up to 12cm (5 inches) long
grow alternately up the hollow stems
• Creamy flower clusters are produced in the late
summer
Autumn/winter
• Plants die back after the first heavy frost, leaving
tall, hollow, tan coloured stems
• Early autumn before the first frost is the best time
to spray
3
GIANT HOGWEED
Heracleum mantegazzianum
Ecology
Giant Hogweed originates from the Caucasus
mountains between Russia and Turkey, and was
introduced as a popular wetland ornamental plant in
the 19th century but it quickly spread as its large
flower-heads produced thousands of small, light seeds
that are easily spread by wind, water as well as by
humans along roads, paths and deliberate planting.
Giant Hogweed is a perennial, growing up from a
single large tap root to a height of 5m (16 feet) and
with leaves of 1m (3 feet). The plant can take several
years to grow to maturity where upon it flowers,
producing up to 50,000 seeds before it dies; the dead
plants can be clearly seen each winter along river
banks, roadsides and even through woodland.
Health Hazards
Their large size and hollow stems mean that Giant
Hogweed is often very attractive to children who use
them as pea shooters and telescopes however the
stems, leaves and sap contain a poison that can result
in serious blistering that reacts badly when exposed to
sunlight. The reaction to the poison can occur up to
48 hours after contact, after only very slight contact,
even through light summer clothing. All blistering
should be treated as a burn and in servere cases
medical advice should be sought as untreated
blistering can lead to permanent skin damage
resulting in discolouration that is sensitive to sun
light and recurrent dermatitis.
4
Identification
Spring
• Dark green, spiky leaves start
growing very early in March/April,
reaching a height of 30-50cm (1215 inches)
Summer
• The large hollow stems are
ribbed and green in colour with
red-purple blotches
• The large, white flower-heads can
be up to 50cm (15 inches) across
Autumn/Winter
• Some immature plants may die
back but many will keep some
colour in their leaves right
through the winter
• Mature, flowering plants will die,
leaving seed-heads with up to
50,000 seeds
Health Hazards
Examples of blistering caused by Giant Hogweed:
• Contact with the poisonous sap on the leaves
and stems of Giant Hogweed can lead to severe
chemical burns, which untreated can lead to
long-term skin damage
• Treat as normal burns, seek medical advice if the
burns are bad or persist
5
HOW TO PREVENT THE
SPREAD OF INVASIVE PLANTS
There are several ways in which the spread of invasives
can be prevented, these include:
• Starting control work as soon as possible
• Where invasives are established along watercourses
ensure work is carried out from the most upstream area.
• If a new area is invaded ensure the plants are controlled
before they are allowed to get established
• Ensure that no seeds or plant segments are removed
from infested areas
• Do not dump cut stems or spread soil containing seeds
or roots of invasive species; just a few seeds or root
segments can cause new areas to become infected
• If in doubt call the Tweed Invasives Officer
6
CONTROL
Non-Chemical Control
Non-chemical control of Japanese Knotweed is virtually
impossible as a means of eradicating the plant, although it
can limit further growth. Grazing can limit the growth and
spread of Japanese Knotweed, however it will often
persist in small pockets that animals cannot access acting
as points of re-introduction after grazing. Cutting and
digging are also means of limiting Japanese Knotweed’s
growth and spread but due to the plant’s ability to regrow from very small segments of either root or stem,
even sections that appear dead, this is not advised. One
of the main means for this plant’s distribution throughout
the UK has been through the cutting and disposal of
plants e.g. strimming waste being taken along roads to
dumps/compost heaps, and through the transportation of
soil with root sections in.
Giant Hogweed can be more successfully controlled using
non-chemical methods than Japanese Knotweed,
although it presents additional problems as great care
must be taken to avoid contact with the poisonous sap.
Grazing using cattle and sheep can be a very effective
means of controlling Giant Hogweed on agricultural land,
especially on steep river cliffs and small, difficult to access
areas along river banks. Best results can be obtained by
placing a small number of livestock in small sections of
infested areas and moving them on as they eat the Giant
Hogweed. Note: riverbanks are not always suitable for
cattle especially if prone to erosion, also note that pigs
should not be used to graze Giant Hogweed as they can
suffer the same burns as humans. Cutting can be effective
for controlling Giant Hogweed although great care should
be taken, ensuring that all bare skin is well covered to
prevent contact with sap which can seep through normal
clothing. Cut plants can often re-grow; to ensure plants
are killed the main tap root should be dug up and cut at
least 6cm (3 inches) below the ground.
7
CONTROL
Chemical Control
Chemical control, i.e. herbicide spraying, is the only sure
means of killing Japanese Knotweed and is also the best
means of killing Giant Hogweed, although it should be
undertaken with great care, ensuring that only the target
species are sprayed and that all safety guidelines are
followed.
Glyphosate-based herbicides are the best for killing both
invasives species as it works by being absorbed through
the plant’s growing leaves and being transported down to
the roots where it blocks the plant’s vital enzyme systems,
thus killing the plants from the roots. Because of the way
glyphosate works it also kills most other types of plants
and therefore should be used carefully and sparingly on
the target species only. Glyphosate is commonly available
for domestic use under the names Roundup and
Tumbleweed, however always read the label before use
and follow the instructions carefully.
Glyphosate is a very safe herbicide and breaks down
quickly in soil and water, however every care should be
taken to avoid contact with the skin and for anything other
than domestic use i.e. other than in gardens, certification
is required and a license is required from SEPA or the
Environment Agency if spraying is to be carried out near
water.
SEPA Offices
Burnbrae
Mossilee Road
Galashiels
TD1 1NF
01896 754797
8
Tyneside House
Skinnerburn Road
Newcastle Business Park
Newcastle Upon Tyne
NE4 7AR
0191 203 4000
CONTROL
Glyphosate Application
Glyphosate can be applied in a number of ways but the
best results are obtained by applying the glyphosate to
the new growth points of the invasives as these areas will
translocate the glyphosate to the roots most effectively.
Glyphosate herbicides can be applied using a weed-wiper
that smears the herbicide directly onto the target plants,
thus avoiding spray-drift and the killing of non-target
species. Spraying is the easiest and most common means
of herbicide application, however care should be taken to
avoid spray-drift and drips killing non-target plants (e.g.
lawns!). After treatment plants may take 2-6 weeks to show
any visible signs of die-back and re-spraying should not be
considered before 6 weeks.
Key Points
1. If you are using agricultural herbicides, spraying on
property that is not your own or are being contracted to
spray, certification is required; this can be arranged
through the Tweed Invasives Officer – this is not
required for domestic use in gardens
2. Always ensure that you comply with all the product
label instructions and do not be tempted to use
stronger dilutions than recommended as this can lead
to environmental pollution, chemical hazards and it also
simply wastes valuable herbicide
3. Always check the weather before applying herbicides as
glyphosate is best applied to dry leaves and can be
washed off by rain, therefore a dry spell of an absolute
minimum of 6 hours is required after spraying and
preferably much more
4. Act responsibly; always discard empty packaging
responsibly and where possible avoid carrying and/or
diluting more herbicide than you require for the job in
hand
5. If in doubt, contact the Tweed Invasives Officer
9
POST CONTROL CARE
Replanting
Once invasive plants have been controlled native plants
should be planted to help reduce the risk of re-infestation,
help prevent soil and bank erosion and to encourage local
wildlife. Suitable species for replanting include native
grass and sedge seeds reflecting the local flora, bramble,
hawthorn, blackthorn and dog rose, and small trees such
as willow and alder.
Health and Safety Reminder
When carrying out activities near rivers, streams or other
water bodies for either work or recreation extra
precautions should always be taken, for example:
• Avoid steep, wet or unstable banks
• Avoid rivers and streams during flood periods
• Watch out for hidden hazards on the banks and in the
water’s margins such as fallen branches, uneven ground
and holes
• Wear the appropriate protective clothing for the task in
hand and the weather conditions
• Avoid going to such areas on your own, so in the event
of any difficulties someone is available to help or raise
the alarm – carry a basic first aid kit
• Observe a strict code of personal hygiene of washing
hands before eating, drinking or smoking
10
Other Invasives
Himalayan Balsam
Impatiens glandulifera
• Very wide spread
throughout the Tweed
• Purplish-pink to light pink
flowers are carried on
succulent pinky-red stems,
with long narrow green
leaves with a red midrib
• The best means of control
is to cut back or remove
flower heads before
germination in late July to
early August
Snowberry
Symphoricarpos albus
• A garden plant that has
gained a foot hold along
hedgerows, river banks and
woodland margins
• A shrub that produces
distinctive juicy, white
berries
Australian Stonecrop
Crassula helmsii
• Can be found in a range of
habitats from damp areas
to deeper pools, prefers
still water, and can grow in
shade and sunlight
• Chokes water courses, outcompetes native plants and
is not edible to native
wildlife
11
THE TWEED INVASIVES
PARTNERSHIP
The work of the Tweed Invasives Project is supported in a
number of ways, by a number of different organisations,
without whom the project would not be able to run. The
following organisations have supported the project, with
many offering practical help and guidance along the way:
(SCOTLAND) LIMITED
The most important partners in this project however are
you, the people of the Tweed catchment, as it is going to
take the vigilance and efforts of everyone to combat the
spread of invasives and the threat they pose to our native
flora and fauna.
12
FURTHER INFORMATION
The Tweed Forum Invasives web site should have
everything you need to know about invasive species within
the catchment - http://www.tweedforum.com/projects/inv
for more information regarding Giant Hogweed and
Japanese Knotweed and how to control them you might
also try the following publications and web sites:
“Guidance for the control of invasive plants near
watercourse”. Available from the Environment Agency,
see web site for details:
http://www.environment-agency.gov.uk/
http://www.ex.ac.uk/knotweed/
http://www.explore-swansea.co.uk/jknotweed.htm
http://www.ecy.wa.gov/programs/wq/plants/weeds/
aqua012.html
http://dnr.metrokc.gov/wlr/LANDS/weeds/hogweed.htm
http://www.cabi-bioscience.org/html/
japanese_knotweed_alliance.htm
If you cannot find the information you are after, or if you
would like to become more actively involved please feel
free to contact Tim Barratt, the Tweed Invasives Officer,
either via email at [email protected] or using the
details below:
Tim Barratt
Tweed Invasives Officer
Tweed Forum
South Court
Drygrange Steading
Melrose
Roxburghshire
TD6 9DJ
Scotland
Tel: 01896 849723
Fax: 01896 849129
13
Technical information correct at time of publication
(February 2003).
The Tweed Forum accepts no responsibility for any loss,
damage or injury arising from the interpretation or use of
information, or reliance upon views contained within.
Produced by the Tweed Forum. For more information
please contact:
Tim Barratt
Tweed Invasives Officer
Tweed Forum
South Court
Drygrange Steading
Melrose
Roxburghshire
TD6 9DJ
Scotland
email: [email protected]
Tel: 01896 849723
Fax: 01896 849129
Or visit our web site:
http://www.tweedforum.com/projects/inv