Hogweed: Why councils and transport managers should be concerned


The health dangers of giant hogweed - an impressive and seemingly innocent-looking plant - have only just come to public attention, while the impact of this invasive non-native species on transport infrastructure managers and local authorities has not yet been widely explored.

Giant Hogweed, sometimes known as giant cow parsnip or hogsbane, can grow up to five metres tall. The sap is toxic and can cause very severe burns and scars. It is mostly found growing alongside footpaths and riverbanks but it is spreading aggressively and now is the time to begin addressing this emerging issue.

Why is this plant, with its impressive umbel of white flowers and thick, bristly, purple-speckled stems, causing such a stir among transport infrastructure managers and local authorities?

Hogweed: Pretty but painful

Along with the more widely known Japanese knotweed, giant hogweed has become a growing problem for a number of reasons. One is that fast-moving vehicles can inadvertently transport seeds, allowing the plant to spread quickly. Trains, lorries and buses can pull seeds along in their slipstream, spreading them across transport corridors and into adjacent habitats, such as the gardens of nearby houses. Many homes and properties on busy transport routes, like the North Circular Road in London, have already been affected.

Local authorities also play a huge role due to the prevalence of invasive species in public spaces, like parks and playing fields, and the perception that it is the council’s duty to tackle the issue.

Property owners close to railway lines, busy roads and local authority land are understandably concerned about the growth of giant hogweed on their land. Besides the potential health risks, there is also concern that the presence of giant hogweed could affect property values in the same way that Japanese knotweed, a similarly invasive plant, has.

The legislation is exactly the same for both plants and homeowners are likely to seek out those whom they believe are responsible. The Wildlife and Countryside Act holds these individuals criminally liable if it is proven they have intentionally contributed to the introduction or spread of non-native species.

Offences may include moving soil that contains the plant to a new location, and in the case of transport managers, non-compliance with the reformed Anti-Social Behaviour, Crime and Policing Act 2014. Under the act’s reformed measures, those failing to address the problems created by plants like giant hogweed could face community protection notices or fines of up to £20,000, which can, if ignored, result in far greater than the cost of tackling the problem before it escalates further.

In January 2015, the new European Union Invasive Alien Species Regulation came into effect, allowing the government to impose Control Orders if transport managers and local authorities fail to manage certain types of invasive plants in a timely fashion. Control Orders issued by government agencies can demand the removal of high-risk invasive weed species from specified areas. A list of these high-risk species has yet to be finalised. Transport managers and local authorities may also be sued under Common Law if one of their employees or a member of the public is injured by giant hogweed on their land.

As a result of these recent developments, there has been a noticeable increase in the number of transport and local authority professionals wanting to better understand the implications of giant hogweed.

So, how should transport infrastructure managers and local authorities tackle the problem? Controlling the plant can be expensive and a ‘scattergun’ approach would drain resources without guaranteeing an immediate and sustainable solution. Therefore, it is important that managers have a good, focused strategy in place for dealing with the plant as effectively and efficiently as possible.

The strategy and implementation plan should include measures such as making sure managers identify where giant hogweed is growing on land or infrastructure. For local authorities, this should include parks and parts of council land, as well as non-council areas from where giant hogweed has spread to council land. Some of this information is available through local environmental records centres and in their growing database of invasive non-native species records.

As soon as a giant hogweed location is identified, measures should be taken to address the problem immediately. Staff working on sites containing giant hogweed should be made aware of the potential risks and what to do in case of contact. Managers should make sure that nylon fencing is erected around giant hogweed plants, coupled with clear signage to minimise the risk of contact between the plant and the public. Managers can also contact local media and use other communication channels to raise awareness of the risk and explain what actions to take if contact is made with the plant, particularly in areas with high levels of infestation.

The next stage is to determine how the giant hogweed was able to invade the site and to take measures to prevent further invasion. This often necessitates collaborating with neighbours to come up with a coordinated package for controlling the offending plants, e.g., along a stream or river. A cooperative approach has been proven to be more successful than a litigious one.

Methods for controlling giant hogweed vary based on factors including available staff and money as well as the target date for control. It is essential to undertake an informed risk assessment and to devise a safe system for work to be performed before any action is taken.

First, stop the plants from producing seeds — and with 5,000 seeds or more coming from a single flower head, this is a priority. Seeds already present in the soil bank can be eliminated by excavating and disposing affected soil, but this can be very expensive. Plants and seedlings can be killed quickly and cheaply by using a herbicide application of glyphosate or, in the case of mature plants, by cutting the parsnip-like tap root. Follow-up monitoring and further control measures are essential if giant hogweed is to be completely removed. The cost of such a programme is reasonable, especially considering the cost implications for transport infrastructure managers and local authorities should someone be injured. A fast, thorough approach is the safest, most effective way to address the issue.

The Property Care Association’s (PCA’s) website lists a range of companies also dealing with invasive plants.

The PCA is running a training workshop for local authorities on invasive plant management, including giant hogweed and Japanese knotweed, on 7 October 2015.

Article by Max Wade, technical director (Ecology) at AECOM and chairman of the Property Care Association’s Invasive Weed Control Group, and Dr Mark Fennell, principal ecologist at AECOM

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