DANGER - Giant Hogweed

It's been mentioned before on this forum, but I thought I would highlight teh dangers of giant hogweed again as it is very prolific on our river banks and around our countryside.

Click here for story.

I read this earlier, it's nasty stuff alright. I didn't know it harmed you through ultra violet light though, I just thought that the sap was corrosive.

If you know where there is some local to me then let me know, it would make a nice gift for my mother in law.

Naaaah, you want ricin, derived from the castor oil plant.......

Alexanders is another to watch out for, sun activated corrosive sap and a great indicator of global warming, is on the protected species list and stated as localy abundant but marching across the country and coming to a place near you soon.

Day of the Triffids?

The tees has forests of the stuff! All part of the summer fun trying to avoid it...


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Its not all bad. Once it is dead and dried it makes lovely kindling for the Kelly Kettle

aebitim said:

Alexanders is another to watch out for, sun activated corrosive sap and a great indicator of global warming, is on the protected species list and stated as localy abundant but marching across the country and coming to a place near you soon.

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Are you sure about this?
Might want to see this Alexanders, Smyrnium olusatrum Seeds
Never known any non-native plants to be put on the protected species list in the UK.
did you mean the Invasive Species List?

Matt you are 8 weeks late with this one mate. It's all dying back now. I did for the last remain plants on one of our club lengths Sunday. They had set seed and almost dead....well they are now!
Since the start of the season me and my fellow triffid killers have done for over a 1000 plants. With a 98% success rate of kill with no regrowth on one river and about 50% rate on another.

The 98% kill rate was achieved without resorting to the use of herbicides and solely done by cutting at the right time in the plants cycle.
This should not be done unless you know what you are doing and have the correct protective clothing on when doing the cutting and the right tools for the job.

zizea aurea

good thread this , I never took an interest in or was aware of any of these issues till I started reading this forum, cycling home the other day I passed a cordoned off area that has Japanese Knotweed - now I know what it means.

Also we had been raising sensitive plants at work ( new regime no plants allowed now ) as part of their lifecycle my mate has to boil the seeds to start them , I think this simulates the effect of a forest fire which means , to an extent , that the seeds are fire resistant ! In turn that reminded me of how its actually safer and more natural , in some parts of the States , to allow a small ground fire every couple of years rather than prevent any fires and inadvertently suffer a huge fire every 10 years or so.

Fascinating really how there is a symbiosis between lightning striking in a forest and the re-generation of plants.

I'm doing a lot of strimming and will often chop through a stand of Balsam to discover that I just sliced through a hogweed as well. The sap from these chopped plants is constantly spraying me in the face and on bare arms (in T-shirt weather). Am I at risk?

Geoff, is it giant hogweed or the more common, and much smaller strain?

The stuff we get on the tees grows taller than a man!


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we have one stretch in a small cub i,m in that has giant hogweed , there is a baliff that is a a conservationist and knows a great amount about this terror weed , he cuts it back and poisons the roots , but also some of the nasty stuff has touched his skin and has brought about big reddy brown stains of which i am told by him will never go away and all club members have been warned of the dangers. these stains are like large birthmarks and he is now stuck with them , so be warned people this is god awfull stuff to mess with.

I often have no option but to work my way through it sometimes on the river bank. With care, it's ok. I've not been caught by its sap. I can just see me one day falling down a rabbit hole and going face first into it knowing my luck


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geoffmaynard said:

I'm doing a lot of strimming and will often chop through a stand of Balsam to discover that I just sliced through a hogweed as well. The sap from these chopped plants is constantly spraying me in the face and on bare arms (in T-shirt weather). Am I at risk?

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YES Geoff you are! And Chubberbob is correct in what he says.

My advice to anyone strimming on the river is full Personal Protective Equipment including a plastic visored face mask and gloves. Not the meshed one that come as a package with the strimmer.
Risk assess the area to be strimmed first, by a walkover to make sure there is no Gt. Hogweed present. If present, leave a 3 M circle around it not strimmed. Yes the plant can have that much spread. Complete the strimming first then deal with the hogweed last still in full PPE.

Two ways of cutting hogweed, either using a very sharp sickle that will cut through it with one blow or a fold up pruning saw that will saw threw the main stalk.
1) First take off all the lower leaves to a height of about 3 ft so you can see the main stalk and swing or get in to saw it unhindered.
2) Cut the plant about 4 - 6 inches above the ground with one blow (sickle) or several pulls with the pruning saw. Despite the large diameter of the main stalk it cuts quite easily, unless you try to cut it where there’s a knot segment. So avoid cutting it at the knot.
We tend to leave the plant where it’s been cut rather than move it. By moving it there is the risk that you inadvertently get the sap on you and the very real risk of burns.

A warning notice on the car park gate is helpful that there is freshly cut Hogweed on the banks and it must be avoided.
Within 3-5 days the plant poses no risk to anyone.

Optimum time to cut it is a week or so after the flower head has bust into flower and before the seed forms and start to ripen.
The plant by this time has put all its energy into flower formation and has none left to regrow a new central stem.

Hogweed btw is a spring and very early summer plant and under normal conditions would be setting seed by mid July. It was very late this year.

Can I stress again it should not be touched unless you know what you are doing and you are wearing full PPE.

One last point as Knotweed has been mentioned, do not strim, cut or dig this stuff, as it will only encourage the plant to spread. It is an offence under the Wildlife and Countryside Act to do any of the above. The plant once cut is classed as Special Waste (TOXIC) and can only be dealt with by a specialist waste contractor for removal to a Special Waste site. Where it must be buried 10 metres deep.

It can be treated on site by a specialist herbicide contractor that holds all the spraying licences needed to do this.
Do not attempt to do this yourself or as a club as the fines are very high indeed, when you are caught.

Thanks for that Phil. Any advice about my main problem, Himalayan Balsam? I have acres of it.
More specifically, what's your take on Roundup Pro? There's a lot of conflicting advice online with a lot of highly respected Pros telling me there's no problem... and then there's the treehuggers and this:

The World According to Monsanto | Watch Free Documentary Online
Excellent viewing when you get an hour or so spare.

Bearing in mind that in my life time we have had expert scientific opinions telling us all kinds of reassuring rubbish (tobacco, thalidomide, climate change deniers etc) I'm trying to get as much experienced opinion as I can before I start spraying this stuff anywhere near a river.

Geoff here's the cover my bum line. You should not do any spraying in the open environment without holding a PA6a and if within a metre of the waters edge Pa6aw. Both of which are for handheld applicators with knapsack sprayer.

Chemical analysis used by the powers that be can detect pesticides (generic term for all cides) down to very minuscule quantities. Seem to remember the figure 50,000 ppm being mentioned.
I'll pm you privately re Roundup products.

Would I be right in thinking the acres of Balsam you're talking about are on the Wye? If so I'll stick some info in the pm for you that might help.

Balsam is an annual plant, therefore it needs the seed each year for the following year to continue to grow. The seed is said to be only viable for 12 months. Personally I think it longer than that up to 3 years.

We are currently running some tests on it to find out the best method of mechanically getting rid of it without having to resort to using pesticides.

It's said that if you pull it up and crush it, it will not regrow in the pulled area. As I said because I think the seed in the seedbank lasts longer than thought, my view is it needs a programme running at least 2 years and 3 would be better.

Our interim, and I must stress it is interim findings, as they are in its first year, has found that sickle cutting or strimming low to the ground when the flowers are on the plant and have been for a week to 10 days, stops it regrowing and producing more flowers and seed pods.

If its cut to early it will regrow new flowers.

Watch this space for more next year

One of the problems with this plant is that it actively disperses its seeds. If the balsam is prolific upstream of you as I suspect it is then a concentrated and united effort is required by all parties if any serious attempt is to be made to remove it.

just for info though I am sure anyone is capable of googling

Himalayan balsam / Royal Horticultural Society

aebitim said:

One of the problems with this plant is that it actively disperses its seeds. If the balsam is prolific upstream of you as I suspect it is then a concentrated and united effort is required by all parties if any serious attempt is to be made to remove it.

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Correct, but in our case the upper catchment has been cleared by the River Trust, mainly by pulling it using it's 100s of volunteers. Pulling it is very labour intensive and slow. What we as a club are looking to achieve is a quicker more efficient method of dealing with it. The tests are to establish this as none of the "experts" can give us a best method.
When done it will form the template for managing it on all our extensive river lengths.