Giant Hogweed
(Heracleum mantegazzianum)

Name and Family
History
Identification Guide
What it does in the ecosystem
Management
Map
Image Gallery
References

Name and Family

Giant Hogweed, Heracleum mantegazzianum, is a member of the carrot (Apiaceae) family.

History

Giant hogweed originates from Asia.
It was introduced to North America as an ornamental garden plant. It was favoured for its size and low-maintenance growth..
It is now found in many provinces throughout Canada and a number of US states.
There are only a few known infestations on PEI, and all are contained within private gardens.

Identification Guide

Giant hogweed has a several lookalikes that grow on PEI.
Native lookalikes include cow parsnip, seaside angelica, spotted water hemlock, and purple-stemmed angelica.
Invasive lookalikes include woodland angelica, wild chervil, and Queen Anne’s lace.
Grows much taller than the lookalikes, up to 5 m tall
Umbrella-shaped inflorescence can be up to 1.5m in diameter and blooms in June-August.
Stem is hollow and covered with coarse hairs and raised purple bumps (these look somewhat like pimples)
Leaves are deeply-lobed, have sharply-jagged edges and 3 leaflets
- These leaves look somewhat like giant, jagged-toothed maple leaves.
Seeds are oval-shaped with 4 dark lines

What it does in the ecosystem

Giant hogweed is one of the most hazardous invasive plants found on PEI. Its spread has negative ecological, economic, and health effects.
Giant hogweed certainly earns its name. Its colossal size, growing taller than humans, allows a single plant to occupy a large area, easily crowding out native species for space and light.
It can grow to form dense monoculture stands in several diverse habitats. It germinates earlier than most native plants, giving giant hogweed an advantage.
Giant hogweed goes to seed only once in its lifetime but produces anywhere from 20,000 to 100,000 seeds per plant.
Giant hogweed is an extremely invasive plant, with infestations causing significant reductions in local biodiversity.
Skin contact with the sap of giant hogweed can produce a nasty burn.
- A compound in the sap (furanocoumarins) reacts with light and skin to cause severe burns, blistering, and eventually dark scarring.
- The sap is most abundant in the lower stem but can be found in all plant parts. Extreme caution should be exercised if you are working near giant hogweed due to this health risk. Never touch the plant with bare skin or skin covered in absorbent fabric.
- Wildlife and livestock can also be subject to hogweed burns. This means that habitat and pastureland can be degraded in affected areas, as animals will have to avoid the giant hogweed.
- Burns can cause long-term sensitivity to sunlight in the affected area for several years after the initial burn.
- Purplish or white scars may form that last for many years.
All of these undesirable characteristics create a significant economic impact for control and awareness.
Removal will require the purchase of costly protective equipment, and giant hogweed infestation may result in reduced property values. Early detection and management of this plant is ideal.
Giant Hogweed is generally found along roadsides, in ditches, along streambanks and in disturbed waste areas.

Management

Personal protection:

When controlling giant hogweed, the following should be worn:
- Tyvek coverall
  - Alternatively, two layers of non-absorbent clothing that completely covers the skin.
- Face shield
- Waterproof gloves
- Sunscreen
- Rubber boots (steel-toe if possible)
- Non-absorbent long-sleeve shirt, and long pants (synthetic fabrics).
Tape any gaps in clothing with waterproof tape.
You should have a water source nearby to wash your skin in case of accidental contact with the plant.

General considerations

Due to the inherent dangers of managing giant hogweed, it is important that you consult with a professional before beginning removal work. The PEIISC is very eager to know about any outbreaks of giant hogweed on PEI, and we would be happy to provide guidance to on controlling this species.
Before beginning management, make sure it is indeed giant hogweed you are dealing with.
- The plant has many native look-a-likes including cow parsnip, purple-stemmed angelica, and seaside angelica.
- Woodland angelica, common valerian, and wild chervil are lookalikes that are also invasive.
- Some people even confuse giant hogweed with Queen Anne’s lace, even though it is much, much smaller.
- All of these lookalikes pose hazards to humans in some degree.
Begin management early in the spring when plants are relatively small, preferably in May to early June.
- This will also allow you to manage the plant before it flowers or gets too large, as smaller plants are easier to manage.
If managing after flowers have formed, carefully cut and remove seed heads and place them in a clear plastic bag to prevent accidental dispersal of seeds that may have formed. You may need to place the bag over the seed head before making the cut to prevent seed dispersal.

Manual control

Giant hogweed outbreaks can be managed by manually digging up the plant.
The goal is to remove the entire plant, including the whole root system, to prevent regeneration from left-behind roots.
Using a shovel, dig into the ground a few inches away from the base of the stem.
- Dig straight down, burying the whole shovel head into the ground.
- Lift the dirt carefully to avoid breaking the roots.
- You can wiggle the plant while moving the shovel back and forth, and the plant should come out of the ground without much breakage.
- If the root crown is broken off, it is important to dig it out, as the plant will otherwise resprout.

Mechanical control

Mechanical controls such as trimming with mowers or string trimmers are not recommended for giant hogweed management, as these practices can spread the sap unnecessarily, creating a health risk.

Chemical control

The PEIISC does not provide advice on chemical control methods at this time.
If using chemical controls, it is imperative that all local legislation and manufacturer’s instructions be followed during application.
Chemical treatment should never be applied nearby a watercourse, as this is unlawful on PEI and can cause unintended ecological damage.

Buffer zone work

When managing invasive species around a watercourse, one must obtain a Watercourse, Wetland and Buffer Zone Activity Permit from the Department of Environment, Energy, and Climate Action.
This permit should be applied for a minimum of six weeks before work commences.

Cleanup, follow-up, and disposal

Sometimes, the most dangerous part of giant hogweed management can be disposal.
- The plants may need to be compacted and broken when fitting them into the disposal container/bag. Compaction and breakage can cause spraying and release of sap, leading to a higher risk of injury
- Do not let your guard down during this stage. You may be itching to get off your gear at this point, but this is not a good idea.
- Make sure your face (and all other body parts) is completely protected. Tuck down your face shield even though it may fog up.
All contaminated equipment must be cleaned thoroughly using soapy water to remove sap and plant parts before leaving the site.
Use all PPE when cleaning and be careful not to touch any contaminated equipment with bare skin.
Collect and bag all plant parts in clear plastic bags, and allow the bagged material to stay outside to get strong sun exposure for a week.
- Leave bags open in a place free from human and wildlife traffic to allow moisture to escape.
All bags should be double bagged, marked as “invasive species” or “giant hogweed”, and properly disposed of in your black waste cart or at a Waste Watch Drop-off Centre.
- Double-bagging will help prevent waste handlers from being exposed to toxins during processing.
- Up to two additional bags can be placed beside the waste cart for collection if your bin is full.
- Never place invasive plants into the compost. This may allow them to become established in the compost heap.
Loads larger than what will fit in a ½ ton truck will require a special permit to be obtained. Reach out to the PEIISC if you would like specific disposal advice.
It will be necessary to return to the site regularly to manage any new growth that may arise.
Replanting the site with native vegetation after you’ve started to deplete the seed bank of giant hogweed can help to regenerate the area.