Controlling Hogweed

[David Crook]

When dealing with Hogweed using a strimmer/brushcutter be very careful as the sap can cause a photosensitive reaction if it gets onto your skin and can cause blistering that takes some time (weeks!) to subside. It can also flare up again if you expose the affected skin to sunlight, so if you are using a strimmer/brushcutter be very careful to cover up all exposed skin. The blistering/reddening reaction seems to appear after a couple of days so it’s not immediately obvious what has caused it. As far as I can see from a bit of internet research, the sap of both giant and common hogweed can cause this photosensitive reaction.

The best way to keep it under control as it is so invasive is to dig out the tap root but this is a tedious and hard task even over a small area. Another good way to keep it under control is to use a short blade scythe or other method to cut it off at ground level although this doesn’t deal with the root. Try to deal with the plants shortly before seeding so that the maximum amount of energy has gone into growing and producing seed heads in the hope that this will have weakened the root enough to not come back so vigorously next time. You will need to keep doing this to keep weakening the plant until eventually you will get some control over it.

Anyone else got any other ideas?

[David Crook]

People often ask how do you tell whether you have Giant or Common Hogweed? Giant Hogweed is very large - up to 3.5 m (11 ft) high, flower "umbels" up to 50 cm (18 in) across, seeds about 13 mm long (1/2 inch). But common Hogweed can get large - up to 2m (a bit over 6 ft) isn't unusual, the umbels up to 15 cm (6 in) across and seeds about 8 mm long. One difference that can help is that the stems of Giant Hogweed typically have reddish or purplish spots; common Hogweed stems are unspotted. Giant Hogweed isn't common in the south-west - but can occur.

This website has photos of UK umbellifers, including hogweed (Heracleum sphondylium) and giant hogweed (Heracleum mantegazzianum): https://www.first-nature.com/flowers/~apiaceae.php . The leaves are quite different.

There’s another comparison of the two species here from a Devon-based ecological consultancy, indicating that they rarely see giant hogweed: https://www.acornecology.co.uk/invasive-species/

But is hogweed really a problem? In some places and to some people Common Hogweed is a weed, and in others places and to other people it isn't! It depends what else you currently have in your meadow and what you want your meadow to be. Perhaps if the Hogweed is out-competing orchids or smothering other delicate flowers then control it, but if your meadow is quite improved, fertile and currently not very species-rich then it could be a good option just to go with it. Seeing the Hogweed Bonking Beetles at it makes it very difficult to think badly of the plant! There's no single type of meadow, and it's difficult to say that one type of meadow is more valuable than another. If your aim is to create a wildlife-rich habitat, like everyone with a meadow, you have to work within the constraints of what your meadow currently is and what management you are able to carry out. Yours could be a magnificent Hogweed meadow! Here is an article in praise of Hogweed - https://community.rspb.org.uk/wildlife/ ... on-hogweed.

By the way, sheep love to eat hogweed so they can help in its control.

[Amy]

I had inadvertently allowed hogweed to spread in a wet grassland area not grazed by livestock - gosh, how quickly it can spread! For 2 years, I sprayed it and I hated it with a passion.

Then I noticed that the red deer were seeking out and eating the hogweed flowers in the next door field. They were enjoying it so much there was none left to seed. I researched the plant to find that it seems to be either a biennial or a short lived perennial. Last year I started an experiment - to allow it to grow and flower unchecked in the first (non deer inhabited) wet area, and then to meticulously deadhead the seedheads. Deadheading took me about 20 mins every 2 days. (Lockdown year!) It has to be meticulous as one missed stem will soon ripen and dry out, and, at the slightest touch, shatter, spreading seeds everywhere. Meanwhile throughout mid summer, I observed all the flies and beetles on the flowerheads with increasing interest, and a forest of 5' high hogweed flowerheads can be quite attractive in a statuesque way. Deadheading also meant I could leave all the tall stems for overwintering insects. Goodness knows if they have actually been used, but now in late winter, I can see holes nibbled through the stems.

I have spread some of the seeds in an area of the next door field to lure the deer nearer so we can watch them. This summer will show if I have managed to turn the hogweed from an unwanted weed in one area to a useful deer attractant in another.

PS a BBC Norfolk podcast The Countryside Hour (which is a brilliant weekly series of observations on wildlife by a very knowledgeable Norfolk farmer) mentioned that hogweed stems are used by ladybirds to overwinter. https://www.bbc.co.uk/programmes/p02tfh ... des/player

PPS http://www.magnificentmeadows.org.uk/as ... ogweed.pdf Magnificent Meadows = even Plantlife discusses controlling hogweed. The article says a "list of associated invertebrates can be found on the Biological Records Centre website", though perhaps you have to log in there, as the link does not work.

And another PS - mid June - just found a mass of bug larvae on the underneath of some hogweed leaves, busy shredding them.

An article by a very observant artist and amateur naturalist on the insects using hogweed - lovely pictures: https://arthropedia.co.uk/heavenly-hogweed/

[Jane W]

Just a quick word in praise of hogweed....as it is just in flower in one of my fields. It is just lovely, and completely covered in insects of the interesting kind.

There are some plants where I feel the name directs how we think of it. 'Meadow sweet' or 'sweet Cicely' are never considered 'weeds'.

Agreed you do have to be a bit careful not to get the sap on your skin, but apart from that I find it a lovely meadow plant.

I'm very interested to hear that things (deer etc) like to eat it, you'd imagine that sap was too strong.

It seems to be slightly on the wane in my field, which I'm very sad about, but I guess, like everything else, it's just reflecting the soil, and light, and moisture, and predator conditions of the environment, and it will come and go based on that.

[Ruth @Ditty]

I'm really pleased to see mention on here about hogweed. I have a hogweed 'meadow' in my 'rewilded' valley, but within that area I also have approximately 40 other plants species which appear either before the hogweed, or alongside it. The flowers are covered with invertebrates, many of which I can't identify but include: sawflies, furry bumblebee mimics (a type of hoverfly which like to tunnel the roots of hogweed in the autumn) and dance flies. If you wish to have fewer plants it is best to take all the tops off before they seed, but hopefully not before all the insects have had their fill!