When property owners think of invasive weeds, Japanese Knotweed is often the first and only culprit that comes to mind. While its destructive potential is well-documented, a recent presentation by the Property Care Association (PCA) sheds light on a family of plants that pose a more direct and severe threat to our health: Umbellifers.

Robert Mitchell, our respected expert in the field, warns that while knotweed can damage property, certain members of the Umbellifer family, which includes common plants from the carrot family, can cause serious physical harm. “Japanese Knotweed does not put you in hospital,” Mitchell states starkly in his presentation, “some Umbellifers will and some can kill.”

This crucial distinction highlights a significant gap in public awareness. Many of these invasive plants are often mistaken for harmless native wildflowers like Cow Parsley, but the consequences of misidentification can be severe.

The Hazardous Duo: Giant Hogweed and Hemlock

Two of the most notorious Umbellifers found across the UK are Giant Hogweed and Hemlock. Understanding the unique dangers each presents is vital for the safety of your family, pets, and employees.

• Giant Hogweed (Heracleum mantegazzianum): This towering plant is phototoxic. Its sap contains chemicals that, when exposed to sunlight, can cause severe blistering, burns, and painful skin inflammation. These injuries can lead to recurring blisters and permanent scarring. Even a small amount of sap in the eyes can cause temporary or permanent blindness.
• Hemlock (Conium maculatum): Known historically as the poison that killed Socrates, every part of the Hemlock plant is highly toxic if ingested. It contains potent alkaloids that affect the nervous system, potentially leading to respiratory failure and death in both humans and livestock.

The Cost of Delay is More Than Just Financial

Allowing these invasive species to establish a foothold on your property leads to an exponential increase in both risk and removal cost. As demonstrated in the PCA’s presentation, the growth and cost of managing an infestation follows a steep curve. The longer you wait, the more expensive and complex the problem becomes.

These plants spread relentlessly. A single Giant Hogweed plant, for instance, can produce tens of thousands of seeds each year, which can easily disperse to neighbouring land.This not only increases the contaminated area but can also lead to disputes and potential legal issues with neighbours. Furthermore, dense infestations degrade the natural environment, reducing biodiversity and the amenity value of your land.

How to Spot the Threat

Correct identification is the first step in managing these hazardous plants, but it can be challenging as many Umbellifers look alike. If you suspect you have one of these plants, do not touch it. Here are some key features to look for from a safe distance:

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Image showing Giant Hogweed in seed.

Image showing giant flower head (umbel) of Giant Hogweed. NB PPE.

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Winter stem of Giant Hogweed

Giant Hogweed

• Gigantic Size: Can grow up to 5 metres tall.
• Spotted Stem: The hollow, ridged stem is covered in stiff white hairs and distinctive purple or reddish blotches.
• Huge Leaves: The leaves are enormous, deeply incised, and can measure up to 1.5 metres wide.
• Massive Flowers: Features large, umbrella-shaped clusters of white flowers that can span up to 80cm across

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Hemlock stem showing the distinctive purple speckling

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Hemlock

• Tall Growth: Typically grows up to 2.5 metres.
• Spotted, Smooth Stem: The hollow green stem is hairless and marked with purple speckles.
• Fern-like Leaves: Its leaves are fine and feathery, similar in appearance to parsley.
• Distinctive Smell: The plant often has an unpleasant, mouse-like odour.

Professional Intervention is Essential

Given the serious health risks and the difficulty of correct identification, tackling these invasive weeds is not a DIY job. As a member of the Property Care Association (PCA), we are held to the highest standards of technical competence and safety.Our accredited specialists can:

• Accurately identify the species on your property.
• Safely and effectively eradicate the infestation using professional methods.
• Provide guidance on preventing future growth and ensuring the safety of your property.

If you have spotted a plant you suspect could be Giant Hogweed, Hemlock, or another invasive weed, your safety is paramount. Contact us today for a professional survey and expert advice. Don’t wait for the problem to grow.

The post Beyond Knotweed: The Dangerous Weeds Lurking in Your Garden appeared first on Conservation Land Services.

1. Understanding Giant Hogweed
2. The Impact of Giant Hogweed in the UK
3. Identifying Giant Hogweed
4. Safety Precautions When Dealing with Giant Hogweed
5. Step-by-Step Guide to Control Giant Hogweed
6. Preventing Future Giant Hogweed Growth
7. Conclusion

Understanding Giant Hogweed

Giant Hogweed (Heracleum mantegazzianum) is a non-native, invasive plant species that originated from the Caucasus Mountain region between Eastern Europe and Western Asia. It was introduced to the UK in the 19th century as an ornamental and architectural plant due to its impressive size and striking appearance. However, its rapid growth and aggressive spread soon led to its classification as a harmful invasive species. This towering plant, capable of reaching heights of up to 5 metres, poses serious threats to both human health and local biodiversity.

Giant Hogweed is a member of the Apiaceae family, which also includes carrots, parsley, and celery. It is a biennial or perennial plant, meaning it takes two years to complete its life cycle or can live for several years. In its first year, Giant Hogweed grows as a rosette of leaves close to the ground. In its second year, it produces a tall, hollow stem with large, deeply lobed leaves and umbrella-shaped white flower clusters.

The Impact of Giant Hogweed in the UK

The introduction of Giant Hogweed to the UK has had significant environmental and health impacts. Its rapid growth and aggressive spread allow it to outcompete native plant species for resources such as light, water, and nutrients. This can lead to a decrease in biodiversity and disrupt local ecosystems.

Moreover, Giant Hogweed poses a serious health risk to humans. The plant’s sap contains a toxic compound called furanocoumarin, which can cause a condition known as phytophotodermatitis. When the sap comes into contact with skin and is exposed to sunlight, it can cause severe skin irritations, blisters, and burns. These reactions can occur within 15 minutes of exposure and may last for several months.

Furthermore, Giant Hogweed can also impact land use and property values. Its presence can make areas unsafe for recreational activities and reduce the aesthetic appeal of gardens and parks. The cost of controlling and removing Giant Hogweed can also be substantial, placing a financial burden on landowners and local authorities.

In response to these impacts, it is crucial for UK residents to understand the importance of controlling Giant Hogweed and take necessary actions to prevent its spread.

Identifying Giant Hogweed

Example of a Giant Hogweed leaf.

An example of Giant Hogweed with Common Hogweed in the foreground

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Image showing giant flower head (umbel) of Giant Hogweed. NB PPE.

Image showing Giant Hogweed in seed.

Winter stem of Giant Hogweed

Before you can control Giant Hogweed, it’s crucial to identify it correctly. Look for large, umbrella-shaped white flower clusters, purple-spotted stems, and deeply lobed leaves that can reach up to 1.5 metres in width. Here’s a seasonal guide to help you identify this invasive species throughout the year:

• Spring: In early spring, Giant Hogweed emerges as a rosette of deeply lobed, dark green leaves. These leaves can be up to 1.5 metres in width and have a shiny, waxy appearance. The stems are purple-spotted and covered in coarse white hairs.
• Summer: As summer approaches, the plant begins to bolt, producing a tall, hollow stem that can reach up to 5 metres in height. The stem is stout and rigid, with purple blotches and bristly hairs. In late summer, the plant produces large, umbrella-shaped white flower clusters that can be up to 80 cm in width.
• Autumn: After flowering, the plant produces numerous green, ribbed seeds that turn brown as they mature. These seeds are held in flattened clusters that can be up to 15 cm in width. The plant begins to die back in late autumn, leaving behind a hollow stem and a large rosette of leaves.
• Winter: In winter, Giant Hogweed dies back almost entirely, leaving only a large, fleshy taproot in the ground. This taproot can be up to 50 cm long and 8 cm in diameter. It is cream-coloured with a brown, corky exterior.

Giant Hogweed can be easily confused with other, less harmful plants, such as Cow Parsley and Hogweed. If you’re unsure about the identification, it’s best to seek advice from a professional or your local council before taking any action.

Safety Precautions When Dealing with Giant Hogweed

When dealing with Giant Hogweed, safety is paramount. Always wear protective clothing, including gloves, long-sleeved shirts, and trousers. Avoid contact with the plant’s sap and wash thoroughly if any contact occurs.

Step-by-Step Guide to Control Giant Hogweed

Controlling Giant Hogweed can be a challenging and potentially hazardous task, often best left to professionals. Here’s a step-by-step guide emphasising the use of professional services and noting the potential adverse effects of chemical control methods.

Identify the Problem 

Correctly identify Giant Hogweed on your property. If you’re unsure, consult with a professional who can confirm the identification.

Assess the Situation

Determine the extent of the infestation. For large or widespread infestations, it’s highly recommended to seek professional assistance.

Hire a Professional

Look for a reputable, licensed contractor experienced in controlling invasive species. They will have the necessary equipment, knowledge, and safety measures to effectively and safely manage Giant Hogweed.

Chemical Control Methods

While herbicides can be effective, they should be used with caution due to their potential environmental impacts. Herbicides can harm non-target species and contaminate water bodies if not used correctly. Therefore, it’s best to have a professional apply these chemicals.

Non-Chemical Control Methods

These methods, such as cutting or digging out the plant, can be labour-intensive and must be done carefully to prevent regrowth. Always dispose of plant parts responsibly to prevent further spread.

Monitor and Follow-up

Regularly monitor the treated area for signs of regrowth. If Giant Hogweed reappears, contact your professional service to discuss further treatment options.

Educate Others

Share your experiences and knowledge about Giant Hogweed with your community. Education is a powerful tool in preventing the spread of this invasive species.

Preventing Future Giant Hogweed Growth

Preventing the spread and future growth of Giant Hogweed is as important as controlling existing infestations. Here are some expanded steps to help ensure this invasive species doesn’t return to your property:

Regular Monitoring

Regularly inspect your property, especially areas prone to Giant Hogweed growth such as riverbanks, ditches, and waste grounds. Early detection can make control efforts easier and more effective.

Proper Disposal

If you’ve removed Giant Hogweed from your property, ensure all plant parts are disposed of properly. Do not compost these parts as they can still produce viable seeds. Instead, seal them in heavy-duty plastic bags and send them to a landfill or incinerate them where local regulations permit.

Avoid Seed Spread

Giant Hogweed produces a large number of seeds that can remain viable in the soil for several years. Avoid activities that can disturb the soil and bring these seeds to the surface, such as digging or tilling.

Maintain Healthy Ecosystems

A healthy, diverse ecosystem is more resistant to invasive species. Encourage the growth of native plant species to outcompete any potential Giant Hogweed seedlings.

Control Waterways

Giant Hogweed often spreads through waterways. If you live near a river or stream, consider installing barriers to prevent the movement of seeds downstream.

Educate Others

Share your knowledge about Giant Hogweed with your community. Teach them how to identify the plant, the dangers it poses, and how to prevent its spread.

Report Sightings

If you spot Giant Hogweed in a new area, report it to your local council or invasive species management agency. Early detection and reporting can prevent new infestations from becoming established.

1. PlantTracker: This is a citizen science project where you can report sightings of various invasive plant species, including Giant Hogweed. You can submit your findings through their website or mobile app. Website: PlantTracker
2. The Non-Native Species Secretariat (NNSS): The NNSS is a UK government initiative that provides a reporting system for invasive species. You can report Giant Hogweed sightings through their online reporting form. Website: NNSS Reporting Form
3. Your Local Council: Many local councils in the UK have their own systems for reporting invasive species. You can usually find this information on your council’s website. If you’re unsure who your local council is, you can find out using the following link: Website: Find your local council
4. The Wildlife Trusts: Some local Wildlife Trusts also accept reports of invasive species. You can find your local Wildlife Trust using the following link: Website: Find your local Wildlife Trust

By following these steps, you can significantly reduce the risk of future Giant Hogweed growth on your property and in your community.

Conclusion

Controlling Giant Hogweed is a responsibility shared by all UK residents. By understanding this invasive species, taking necessary safety precautions, and following effective control methods, we can protect our local biodiversity and ensure the safety of our communities.

Because giant hogweed can cause severe burns, removal is best left to professionals. See our giant hogweed identification and removal service.

The post How to Control Giant Hogweed: A Step-by-Step Guide appeared first on Conservation Land Services.

In a word, yes. This particular invasive weed species to the UK (originally native to Central Asia) can cause some nasty burns and even blistering, but what is not very well known is that it will continue to cause severe blistering in the following season and sometimes the season afterwards. That is, let’s say you touched it in 2022 and had blistering, unless you cover your skin up, even though you do not touch it in 2023, you will also have blistering in 2023 and sometimes even in 2024.but what makes (Heracleum mantegazzianum) Giant Hogweed Poisonous?

Giant Hogweed sap and phototoxicity

The sap of the Giant Hogweed plant can produce a mild rash to watery blisters and possible chronic dermatitis, all of which may require hospital treatment. It prevents the skin from protecting itself from sunlight which leads to a very bad sunburn. 

The Giant Hogweed sap contains a family of compounds known as furanocoumarins (referred to as furocoumarins), it’s these photosensitizing furanocoumarins, on contact with human skin in conjunction with sunlight, that can cause phytophotodermatitis.

These compounds are found throughout the entire plant: the flowers, the stems, the roots and seeds. The most concentration of the sap can be found in the leaves.

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The phototoxic effects of the sap’s compounds are due to their interaction with DNA when they absorb UV light of a specific wavelength. UV radiation with a wavelength between 320-380 nanometres can trigger the effects of furanocoumarins.

Furanocoumarins interact with the bases that help hold DNA strands together and ultimately this can cause cell death and results in the characteristic skin reddening and blisters.

Safety Precautions and the need for protective clothing

The correct type of protective clothing should be worn when handling Giant Hogweed due to its potentially dangerous effects on human skin. It is important to consider that absorbent fabrics can soak up sap and allow the transfer of sap onto skin and cotton and linen fibers can be penetrated by plant hairs.

• Prevent UV sunlight from reaching skin by wearing long waterproof gloves, long sleeves, pants, boots, and eye protection.; synthetic water-resistant materials.
• Do not touch the plant with bare skin.
• Apply sunblock before beginning work.
• Do not touch your face or rub your eyes if there is a chance you have any sap on your hands or the outside of your protective clothing.
• Do not use a “weed-whacker” or brush cutter as sap may splatter as stems are cut and can splash three to four feet.
• Launder clothes that may have contacted plants.
• Wash equipment with water immediately after use.

How to treat exposure to Giant Hogweed Sap on skin or eyes

It’s advisable to seek medical treatment if any skin inflammation subsequently occurs from contact with Giant Hogweed.

Giant Hogweed leaves contain more sap in June and the concentration of the active compounds will vary between plants. 

Initial exposure to the sap is completely painless and the reaction is activated by ultraviolet radiation which can begin 15 minutes after contact and will peak 30 minutes to 2 hours after exposure. Heat and moisture (sweat or dew) can worsen the skin reaction.

When coming into contact with Giant hogweed sap, wash the affected area thoroughly with soap and water immediately and keep the exposed area out of sunlight for 48 hours. If sap goes in your eyes, rinse them with water and wear sunglasses.

If a reaction has occurred, the area of skin may be sensitive to sunlight for a few years and you may want to apply sunblock or keep the affected area covered from the sun when possible.

Should you become exposed or if reactions do occur then seek medical attention.

Giant Hogweed UK Hotspots Map

There has been rapid spread of Giant Hogweed across the UK despite the implementation of control measures.

The Botanical Society of Britain and Ireland’s database provides access to the millions of botanical records collated by the society. The data is used to generate the distribution maps is available for academic research and other specialist uses from the BSBI’s network of county recorders, local groups and taxonomic experts. Here is the UK Giant Hogweed Hotspot map.

What not to do with Giant Hogweed

In the UK it is illegal to plant or facilitate the spread of Giant Hogweed and councils take active measures to remove it when its presence is reported. Increasing numbers of articles citing cases of Giant Hogweed burns have been appearing in recent years.

Giant Hogweed is listed on Schedule 9 of the Wildlife and Countryside Act (1981), the same as Japanese Knotweed (Reynoutria japonica) and so is one of the listed non-native invasive species, which requires the landowner to prevent the spread beyond the boundaries of the property into neighbouring land.

Don’t whack, smash or cut the stems of the Giant Hogweed as the sap may splash on unprotected areas of yours or others skin.

Contact a professional service to treat and dispose of the invasive weed safely if it has been identified.

Sources

National Library of Medicine

NHS Highlands

Compound Chem – Explorations of everyday chemical compounds

Botanical Society of Britain and Ireland – UK Hotspot map

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