hogweed is an invasive non-native plant species that is invading
streamside (riparian) areas throughout North America and Europe.
Creek likely has the oldest population of giant hogweed in western
Canada and it is considered the epicenter of invasion on southeastern
hogweed plants can grow up to 5 m tall and produce up to 120,000
seeds upon flowering.
hogweed is a human health hazard. Contact with sap in the presence
of sunlight can cause skin blisters (contact dermatitis).
Invasive Alien Plants Program (IAPP), a program of B.C. Ministry
of Forests & Range, has developed a management
strategy to manage giant hogweed in the French Creek watershed
in association with landowners and interested groups.
hogweed is an invasive plant that is considered both a public health
and environmental hazard. It is common in streamside areas of French
Creek from Coombs to the stream mouth (see map). It was introduced
into the French Creek watershed before the early 1960s. French Creek
likely has the oldest population of giant hogweed in western Canada
and it is considered the epicenter of hogweed invasion on southeastern
Vancouver Island. Giant hogweed is now found from Sooke to Courtenay.
It is also found in the Lower Fraser Valley, particularly North
and West Vancouver.
of giant hogweed in North Vancouver (left) and at Vanier Park
in Vancouver (right)
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and Identification of Giant Hogweed
hogweed (Heracleum mantegazzianum) is a member of the Carrot
Family which originated in the Caucasus Mountains in west central
Asia. In its native habitat it is found in subalpine meadows and
forest edges. It is related to native cow-parsnip (Heracleum
maximum) which occurs in streamside areas, moist forests, and
subalpine meadows throughout BC.
hogweed is identified by its large size (3–5 m tall when flowering),
serrated leaf pattern, and seed morphology. It is sometimes confused
with native cow-parsnip or seaside angelica (Angelica lucida)
although the similarities are superficial. To view a detailed presentation
on how to identify giant hogweed, click
more photos and identification resources for giant hogweed, visit
identifying features of giant hogweed: 1) deeply lobed and toothed
(serrated) leaves; 2) tall stems with extensive purple-reddish blotches;
and 3) seeds with blunt ends and oil ducts greater than 3/4 the
length of the seed.
key attributes of giant hogweed include:
hogweed disperses and establishes by seed. Pieces of roots, leaves,
and stems do not resprout like Japanese knotweed or English ivy.
Seeds are moved by wind (1–4 m) or longer distances by water
along watercourses, ditches, or storm pipes. Each plant can produce
thousands of seeds per plant (up to 120,000 (!) but more typically
establishment of new populations over longer distances is usually
by humans. Gardeners sometimes grow giant hogweed as a specimen
plant and it is suspected that giant hogweed was introduced to
French Creek as a garden introduction. As well, soil or plant
material contaminated with seed is sometimes used for roadfill
or other construction activities resulting in the establishment
of new populations. Small roadside populations are often established
from seeds blowing from trucks during transport of cut plants
or seed heads.
hogweed grows in a variety of soil types and vegetation communities
(forests, beaches, wetland margins) but prefers moist areas with
high-light levels such as streamside areas, forest edges, and
roadsides. It can grow and flower in forested areas but it is
typically smaller and produces fewer seeds.
hogweed grows for 3–5 years before flowering and dying in
the last year. During the first years of growth, it stores increasing
amounts of energy in its roots to put into development of the
flower stalk, flowers, and seeds. Many established populations
consist of plants of varying ages: small first year plants, larger
older plants, and fourth or fifth year plants in flower.
cutting the flower stalk at ground level can be used to kill giant
hogweed. However, it often it develops a secondary flower stalk
and inflorescence and there is also more chance of being exposed
to plant sap when working with larger plants. Removing the seed
head in the summer (June 30–July 15) can prevent the production
and dispersal of new seeds which is sometimes a useful short-term
hogweed seeds may remain in the ground more than five years although
most seeds germinate in the first two years. Control efforts must
include site monitoring to prevent hogweed re-establishment from
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of Giant Hogweed in French Creek
mapping (October 2007; Invasive Alien Plant Program) identified
53 sites in the French Creek watershed with giant hogweed.
All mapped sites are within 50 m of the mainstem of French
Creek. The giant hogweed population is found along approximately
14.4 km of stream channel. Four sites occurred in the lower
developed portion of the watershed (stream mouth to the
E&N rail corridor), ten sites between the E&N rail
corridor and Highway 19, 17 sites between Highway 19 and
Pacific Rim Highway, and 22 sites upstream of the Pacific
Rim Highway in the Coombs area.
Distribution of giant hogweed sites
in the French Creek watershed
(click on map to enlarge)
hogweed stands along French Creek
the overall number of sites increased with increasing distance upstream
from the stream mouth, the mean density of sites declined from 6–10
plants per square meter in the few sites near the mouth, to 2–5
plans per square meter in the Coombs area. It is also important
to note that the existing survey likely underestimates the distribution
of giant hogweed in the watershed. Small patches are likely to be
missed by surveys and it also suspected that more sites may occur
away from the stream corridor. We encourage landowners and stewards
to report new sites using available maps (see Getting
Involved for more information) or using the Report-A-Weed
online invasive plant reporting tool.
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and Safety Issues
hogweed sap contains chemicals which can cause severe dermatitis
(welts, rashes, and blistering, followed by pigmented scarring)
when they contact skin in the presence of sunlight (light-activated
phytodermatitis**). The chemicals, called furanocoumarins, are activated
by sunlight to become irritants. They are found in the leaves, stems,
flowers, and roots of giant hogweed, as well as other members of
the Carrot Family. Contact with plant sap can occur by brushing
against broken plant parts, handling plant material, or even by
touching tools or mowing equipment that was used for giant hogweed
control. Children playing with the large plants, or maintenance
workers or gardeners involved in vegetation control are most likely
to acquire dermatitis from giant hogweed.
are four main recommendations for minimizing the risk of being affected
by giant hogweed dermatitis when undertaking control activities:
protective clothing that covers all exposed skin and eyes when handling
giant hogweed. This includes gloves that are impermeable to plant
juices (thick latex gloves), coveralls or raingear, and a facemask
or safety goggles. WorkSafe BC has issued a Toxic
Plant Warning for workers who may come into contact with this
hogweed can cause severe dermatitis if sap contacts skin and then
is exposed to sunlight (left). Appropriate clothing and safety equipment
should be worn to minimize the risk of exposure (right).
control techniques that minimize the generation, dispersal, and
contact with plant sap. Use a long-handled shovel to cut plant roots,
or a long-handled sickle to cut flower heads. Do not use a brushcutter
or mower unless you have proper training and safety equipment because
they distribute plant sap to exposed surfaces.
you are exposed to giant hogweed sap, wash affected skin as soon
as possible with warm, soapy water or streamwater if you are a remote
area. Rinse eyes immediately. If you are unsure if all plant sap
is removed, keep the area of skin covered (no sunlight) until you
wash thoroughly. Consult a doctor if have extensive exposure to
giant hogweed sap or if develop blisters or other signs of dermatitis;
make sure you tell health care providers about your exposure to
giant hogweed sap.
all clothing and equipment thoroughly with soap and water after
contact with giant hogweed. Be careful not to redistribute plant
sap when washing clothing or equipment.
a WorkSafe BC video and download a Toxic Plant Warning brochure
on giant hogweed, visit the WorkSafe
from giant hogweed is sometimes referred to as phytophotodermatitis
because of the combination of plant sap (phyto) and sunlight (photo)
that is required. The reaction is caused by furanocoumarin chemicals
(psoralens) present in plant sap in combination with ultraviolet-A
light. Other plants in the Carrot Family can cause dermatitis including
celery, carrots, Queen Anne’s lace, and cow-parsnip. Furanocoumarins
are also present in grapefruit and limes.
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recommended control methods for landowners on private property is
manual cutting of the taproot in spring or early
summer or careful use of glyphosate, a herbicide commonly called
Roundup®. Root cutting is the preferred method in most sites
because of its effectiveness. As a secondary measure, the removal
of flowering heads in early to late summer (June 30–September
15) is recommended as a low effort method for preventing further
seed dispersal. However, removal of flowering heads does not kill
hogweed taproots should be cut at least 10 cm below the soil surface
using a sharp long-handled shovel or spade.
for manual root cutting
many members of the Carrot Family, giant hogweed has a deep taproot
that stores energy for annual growth or flowering. The root can
be 12 cm thick and 45 cm long. The large root also provides a buffer
against damage to the above-ground parts of the plant from mowing
or browsing. Giant hogweed can rapidly resprout forming leaves or
a new flower stalk after cutting the leaves and stem.
characteristic can also be exploited for control and we recommend
root cutting as the most effective method of killing small groups
(<100) of giant hogweed plants. The suggested method is to:
Wear protective clothing (see WorkSafe
BC Toxic Plant Warning) that covers exposed skin and glasses
or a face-shield to cover the face and eyes. Gloves are essential.
Using a sharp long-handled shovel or spade, sever the root about
10–15 cm below the soil surface. All plants should be
treated, not just large plants.
the above-ground part of the on-site to decompose unless there
is risk that people will touch them. If possible, do not handle
the plant at all and allow it to rot where it falls. If flowerheads
with developing seeds are present, remove the flowerheads, put
them in a plastic bag, and dispose of them in your household
Undertake one round of root cutting in early spring (April 1–May
15) and a second round in early-summer (June 15–July 15)
to treat any plants that were missed or have resprouted.
Wash any tools that have been in contact with plant sap.
Monitor the site annually for 3–5 years around June 15
to ensure that new seedlings are identified and removed (root
(left) and after (right) root cutting at a giant hogweed control
site in North Vancouver.
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Ministry of Forests & Range is looking for French Creek landowners
willing to participate in controlling giant hogweed in the French
Creek watershed. You can participate in the following ways:
Control giant hogweed on your property. Become familiar
with the methods and safety measures required to control giant hogweed
and conduct removals in late spring or early summer. For large stands
of hogweed, assistance may be available. Contact Jeff Hallworth
(Coastal Invasive Plant Specialist, B.C. Ministry of Forests &
Range) at 250-731-3087 for more information.
Map locations of giant hogweed in the French Creek watershed. Maps
are being mailed to property owners in areas currently known to
have the largest areas of hogweed. If you receive a package, please
record any hogweed locations on your property on the map provided
and return them as requested. If you have hogweed on your property
and did not receive a map, please contact us. Alternately, you can
allow B.C. Ministry of Forest & Range staff to access your property
during July–August 2009 to map any hogweed on your property.
Increase public awareness about giant hogweed in French Creek. Encourage
your neighbours and other landowners to participate in the program.
hogweed information packages will be mailed to select French Creek
landowners in early 2009. To request an information package, a map
of your property, or get involved, call Jeff Hallworth at 250-731-3087.
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Giant Hogweed Best Practice Manual: Guidelines for the management
and control of an invasive weed in Europe. Published by
Forest & Landscape Denmark (C. Nielsen, H.P. Ravn, W. Nentwig,
and M. Wade (eds.), 2005). Download
Plant Warning for Giant Hogweed. WorkSafe BC. Download
presentation on how to identify giant hogweed. Developed
by Nick Page (Raincoast Applied Ecology) for Greater Vancouver Invasive
Plant Council. Download
on Giant Hogweed. Produced by Invasive Plant Council of
Management Practices for Giant Hogweed. King Country Noxious
Weed Control Program, King County, Washington. Download
BC - Heracleum mantegazzianum. Electronic Atlas
of the Plants of British Columbia (www.eflora.bc.ca). by Brian Klinkenberg
(editor), Lab for Advanced Spatial Analysis, Department of Geography,
University of British Columbia, Vancouver. View
Alien Plants Program (IAPP). B.C. Ministry of Forests &
online invasive plant reporting tool. B.C. Ministry of
Forests & Range. Visit
Ornamentals - Giant Hogweed. B.C. Ministry of Agriculture
and Lands. Visit
Guide to Noxious Weeds and Other Selected Invasive Plants of British
Columbia. B.C. Ministry of Agriculture and Lands. Visit
Biology of Invasive Alien Plants in Canada, Giant Hogweed (Heracleum
mantegazzianum). Published in the Canadian Journal
of Plant Science 86 (by N.A. Page, R.E. Wall, S.J. Darbyshire, and
G.A. Mulligan, 2006). Download
mantegazzianum Sommier & Levier. From Biological
Flora of the British Isles series published in the Journal of Ecology
(by G.E.D. Tiley, F.S. Dodd, and P.M. Wade, 1996). Download
and Management of Giant Hogweed. Edited by P. Pyšek,
M.J.W. Cock, W. Nentwig, H.P. Ravn, 2007). Download
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more information on the French Creek Giant Hogweed Project, contact:
Coastal Invasive Plant Specialist
Ministry of Forests & Range
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French Creek Giant Hogweed Project is an initiative of the Invasive
Alien Plants Program (IAPP) of the B.C.
Ministry of Forests & Range with assistance from Raincoast
Applied Ecology. Website developed by Patrick Lilley and Nick
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2009 B.C. Ministry of Forests & Range