If you’re out driving in the UK at this time of year you may have noticed the massive Jurassic Park like plants which are infesting the verges and in some places infringing on the carriageways of many of our roads. This is Heracleum mantegazzianum more commonly called Giant Hogweed
Giant Hogweed (as seen above) isn’t just a spectacular plant it’s a very real risk to human health. The sap of this plant will “burn” your skin on contact and can blind you if it gets into your eyes. Damaging the plant by breaking stems or leaves will release the sap and the fine hairs on the stem and leaves of the plant will deliver the sap in the same way as a stinging nettle. So simply brushing past a plant with your bare skin could be sufficient to cause problems.
The “burn” effect is caused by severe irritation which results in photosensitivity, this will make the affected area extremely painful, with blistering occurring 24-48 hours after exposure and will probably result in dense pigmentation (purple scars). The effects of the photosensitivity may persist for years afterwards causing exposure to sunlight to be very painful.
So what can you do? Well firstly don’t just go out with the secateurs and set about it, I cannot stress strongly enough the risks of getting the sap of this plant on your skin. If you notice this plant on your property you actually do not have a legal duty to deal with it unless it is spreading from your property onto someone else’s or your local authority deem that it represents a risk to the public, in which case you may be served with an enforcement notice.
However, as with all invasive species early action is to be recommended, it’s only going to get worse if you ignore it. If there are no flowerheads then you probably do have some time to plan your response because the plants typically grow for 2-3 years prior to flowering but a smaller plant is always going to be easier to deal with and you really don’t want to allow that plant to reach maturity. If you’re looking out of your window at a plant with impressive white flowerheads just now then you have a few weeks or less to take action before those pretty flowers turn to seeds. When this happens the plant will release a vast number of seeds, in the order of 50,000 seeds can be expected from a single large plant. This is particularly problematic because while it’s rare in the environment for seeds to remain viable for this length of time, under controlled conditions these seeds can remain viable for up to 15 years. Seeds will be distributed by wind and any nearby water courses. So containing it on your property is, in practice very difficult and early intervention could save you a considerable amount of trouble and money.
Giant Hogweed can be controlled by physically destroying the root or treating with herbicides. Herbicides have been found to be most effective when applied early in the growing season and if treating mechanically it is essential to destroy the root. Damaging the rest of the plant only slows it down rather than killing it. So cutting must be done to a depth of around 15cms below ground surface. Obviously herbicides must be applied by a suitably qualified person and we cannot stress highly enough how nasty exposure to the sap of this plant so DO NOT attempt to hack it to bits or dig it up without suitable protective clothing. So, if in doubt talk to an experienced professional.
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