Professor Derek Knottenbelt wrote an article in Country Illustrated magazine Volume 7 Number 70 in the summer of 2004. The author of this site has seen many inaccurate and deplorable articles on the subject but in his honest opinion this is by far the worst. It is full of peculiar statements including many inaccuracies and falsehoods. Just to illustrate how bad the article is, the statements where a problem is encountered have been numbered

It starts with a false claim. (Problem number 1)

THE mismanagement of ragwort in Britain is a national disgrace, Poisonous and aggressive, responsible for the deaths of horses and farm animals, the plant is spreading catastrophically through our meadows and open spaces.

In 2007, three years after the article was written, there was a national survey of plants. It covered the previous years including the time of the article. It actually showed that ragwort had decreased[1].

And it goes on to mislead. (Problem number 2)

But, incredibly, the drive to control the ragwort threat is meeting dogged resistance from pro-ragwort eco-campaigners who deny that ragwort is dangerous to equine health, even to the extent of promoting its protection, citing the cinnebar[sic] moth as beneficiary.

The issue of ragwort is not the cinnabar moth (as it is correctly spelled) but all the other wildlife it supports and the fact that so many inaccurate articles, like the one under discussion here, are written that conservationists with a scientific attitude are infuriated by the falsehoods. Conservationists do not deny that ragwort is poisonous they merely question, with good evidence, whether the claims of extreme danger to animals which are often made are valid. This particular individual webpage is a classic example of a conservationist doing just that, questioning the validity of those claims and having the evidence to prove them false too.

Then there is this extraordinary claim about seed production and germination rates. (Problem numbers 3 & 4)

It produces more than 150,000 seeds, with an expected germination of more than 80% for up to 20 years.

This site has a special page on ragwort seed production. The highest figures are given by a study published in 1957 [2]. It gives total seed per plant figures at 8 sites as
and reaches an exceptional experimentally induced highest figure of 174,230 with plants that have been cut down and prevented from flowering in their second year which produce more seed in the 3rd. A rather exceptional occurrence in nature.

So the 150,000 figure is wrong. In fact an advert produced by an equine charity stating just 150,000 seeds was banned by the Advertising Standards Authority (ASA) , as misleading. The ASA are are independent and look at evidence like this in making decisions. Claiming "more than 150,000" is even more misleading.

Then of course it isn't expected that all those seeds would germinate, we know from research, for example, that some fail to leave the parent plant, so "an expected germination of more than 80%" is simply wrong. On average a plant will have just one offspring. If any plant produced this number of seeds and they all grew to adulthood producing more seeds in the same manner, then it would only be a few generations before their weight equalled that of the earth!

Then he gets the law on ragwort wrong. (Problem number 5)

Classified as a noxious weed in the Weeds Act of 1959, every landowner has since been required to control ragwort either by direct spraying or by lifting and burning.

This site has a page on ragwort and the law. It was one of the first pages created on this site in 2002 and would have been available to Professor Knottenbelt when he wrote the article. Landowners are not required to control ragwort, they may be ordered to "prevent plants from spreading". but in the absence of an order nobody is required to do anything. No requirement exists to spray lift or burn it.

On a point of accuracy (Problem number 6) the Weeds Act does not use the words "noxious weed" at all. The term used is injurious weeds, which actually means harmful to the interests of agriculture. ( The link goes to a detailed explanation.)The other weeds listed appear in books in foraging food for free and are actually edible. Although in excess there could be problems in eating the docks that are listed. The Weeds Act is actually what is known as a "Consolidation Act" which reimplements earlier legislation. In this case this is the Agriculture Act 1920. Agricululture and its effects on the environment and biodiversity were very different in 1920.

Then comes a very misleading paragraph.(Problem number 7)

In Britain, one reason given for arguing against ragwort control is that the plant is purported to be the natural and only food source for the cinnebar[sic] moth.


However, the moth also feeds on common groundsel and other plants when necessary.

This is a straw man argument, where the opponent's argument is misrepresented and then the misrepresentation is attacked. Everyone who knows anything about the moth knows that other plants are occasionally used.

Groundsel is a much smaller plant and more ephemeral in its occurrence. It does not support the moth's population well in the long term.

A research paper in the journal Entomologia Experimentalis et Applicata [3] studied the effects of three plants on the cinnabar moth. These were ragwort (S. jacobaea) groundsel (S. vulgaris) and coltsfoot (T. farfara) Here are the relevant results:-

Larval batches reared on S. jacobaea had significantly lower mortality (<1%) than those on either S. vulgaris (approx. 4%) or T. farfara (approx. 15%, which was also significantly greater than S. vulgaris)

So the caterpillars do better on ragwort. The paper goes on to talk about the egg laying preference of the adult moths.

Adults showed the same hierarchy of preference as the larvae, however they never oviposited on T. farfara.

This research clearly identifies ragwort as the best and most important foodplant.

Then Professor Knottenbelt's article continues ignorantly.

Insects have adapted to food sources for billions of years, and it is patronising to think that elimination or at least reduction of ragwort will result in a catastrophic fall in moth numbers -it did not happen before, when ragwort was under control.

This is quite an amazing set of falsehoods to get from an academic in a biological field. Insects have not been on the earth for billions of years. They first appear in the fossil record at around just 400 million years ago. (Problem number 8) To say that a creature that has evolved to use a particular food source will not be affected by the loss of its food is a bizarrely incorrect statement to make. (Problem number 9) Habitat destruction is one of the main problems that causes extinction. This is like saying we can chop down the Amazon Rainforest and all the wildlife that lives there will adapt. It is a most peculiar claim to make.

It then gets even worse. (Problem number 10)

The cinnebar[sic] moth has in fact become more rare as ragwort has increased. There is strong evidence that too much ragwort, far from being vital to the moth, may be responsible for its decline.

At this point we have to also consider a quotation from Professor Knottenbelt which does not appear in this article but that appears in a book [4]. It seems to put his point over in a clearer manner.

`I would not normally advocate the eradication of any species, but this one has nothing to offer. I don't accept that eradicating ragwort would eradicate the Cinnabar Moth, which feeds on it. Ragwort is burgeoning and the Cinnabar is declining. In fact, I believe it is being poisoned. The moth was common throughout the years that ragwort was rare and now that ragwort is widespread, Cinnabar Moths are difficult to find. If we care about the moth, we have to find out why its population is declining in the face of an ad lib supply of "feed'.

The author of this site tries to present the arguments in a calm, rational manner, but this claim does merit some emotion in order to give an accurate account. This statement from Professor Knottenbelt comes over as positively insane. It is absolutely crazy! It is hard to find a form of words to describe just how ludicrous it is! The plant is the food of the insect. This is what it needs to eat to survive. Surely you would expect a veterinary professor, of all people, to know this?

The article continues (Problem number 11):-

Until the last decade, ragwort was not widely seen.

The plant has always been common. Surveys back into the 1960s show that its distribution has not changed.

From a survey in 2002, the British Horse Society concluded that 6,500 of the 180,000 horses in the UK died that year as a result of ragwort poisoning.

This survey should never be quoted. (Problem number 12) It is simply invalid. The British Horse Society no-longer use it. It was conducted by the British Equine Veterinary Association. It would seem reasonable that Professor Knottenbelt is involved in this organisation as a prominent equine vet. They sent a survey form to all equine vets, but only 4% responded and, in a quite unacceptable abuse of statistical methods, this was multiplied to get a result as if all vets had responded in the same way. No effort was really made to properly establish on what basis a diagnosis was made or to exclude duplicated examples where the same cases were reported by multiple vets. There is actually no way to establish a diagnosis of ragwort poisoning definitively.

A bizarre claim. ( problem number 13)

The poisonous alkaloids have been found in milk and honey, and although the amounts are so small as to be insignificant, the presence of any is unacceptable.

The logic in this is poor surely? If something is scientifically insignificant as a danger then there is no problem!

Then this extraordinary behaviour (Problem number 14)and a wildly wrong estimate of level of poisoning that research would show. (Problem number 15)

I myself have eaten ragwort, then tested my blood. I detected liver damage for two days. You would Expanding this for horses, at Liverpool University we have a research group developing a non-invasive equine blood test, to be used as an early indicator of ragwort poisoning before the clinical signs develop. I estimate that 20% of horses in this country will have ragwort poisoning in their body.

First of all there is no dispute that ragwort is poisonous to people. Deliberately consuming a known poison to prove is poisonous is at best silly and pointless. The work on developing the blood test, which actually didn't involve testing the liver but looking at blood samples, took place. It should be noted that Professor Knottenbelt's claim was that 20% of horses in general would have ragwort poisoning. This would be whether they were ill or not.

The research was done and in 2008 a PhD thesis detailing it was published [5]

These are salient parts of the thesis with an explanation in square brackets.

Whole blood, plasma and haemoglobin from ninety-one clinical cases of suspect ragwort poisoning in horses were screened for ethylether pyrrole content. [ ethylether pyrrole would be the what you would be looking for that would be produced from the breakdown of the alkaloids in ragwort]

Of the ninety-one samples analysed, only one whole blood sample tested positive for pyrrolic ethers.
The sample which tested positive was from a horse which had been neglected and was thought to have been exposed to ragwort at some time.

The claim that 20% of horses would have poisoning was not supported by the results of the experiments. In fact even in symptomatic horses the test only produced one positive case in ninety one cases. A claim that would be expected to terrify horse owners was not substantiated.

Then this is a seemingly scary statement but makes no real sense:- ( Problem number 16)

Recoveries from terminal stage liver failure are not possible.

Terminal cases are exactly that terminal so recovery isn't possible by definition.

Then there is this inaccurate call to action. (Problem number 17)

Anybody who cares about the biodiversity of the British countryside and the welfare Of horses and other grazing animals must lake some responsibility. Even gardener must be vigilant and remove every plant well before it flowers and sets seed. It is not simply a matter of protecting horses - it is a matter of protecting the British countryside.

Just to quote one thing in reply. This is Friends of the Earth's summation of a report on just how ecologically valuable ragwort is.

Ragwort (was Senecio jacobaea now Jacobaea vulgaris) is an important wildflower for invertebrate wildlife: -
35 insect species totally rely on Common ragwort for food including 7 moth and 7 beetle species;-
Another 83 species are recorded as using Common ragwort often as a significant food source, with a further estimated 50 species of parasite in turn feeding on those;-
In addition to these 133 species, Common ragwort is a significant source of nectar for others including bee species that specialise in feeding on yellow Asteraceae (daisies) and many species of butterfly. Government research shows that of over 7,000 plant species in Britain Common ragwort is the 7th most important nectar-producing plant.

By now any reasonable reader should have drawn the conclusion that Professor Knottenbelt not only fails to make his case in the face of the evidence, he just gets things wildly wrong. He is wrong or misleads people so often in the honest opinion of the author of this site that nobody should believe what he says.

The problem is that his academic status has led him to be listened to and repeated by many.

References :-
1. Analysis of data from 2007 UK Countryside Survey . Calculations pers comm Matt Shardlow CEO Buglife.
2. Harper, J.L. & Wood, W.A. (1957).Senecio jacobaea L. J. Ecol., 45,617-637
3. Tinney, G. W., Hatcher, P. E., Ayres, P. G., Paul, N. D., & Whittaker, J. B. (1998). Inter- and intra- species differences in plants as hosts to Tyria jacobaeae. Entomologia Experimentalis et Applicata, 88(2), 137-145.
4. The Horse and Pony Care Bible in Association with Horse and Hound 2007.
5. Moore R.E. Novel Strategies for the Detection of Ragwort Poisoning in Horses. (2008) PhD Thesis University of Liverpool.

Ragwort Home

Ragwort Myths

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Ragwort Horse deaths

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Professor Derek Knottenbelt.