Ragwort An Open Letter to Alastair Stewart

Today's blog entry is prompted by several Tweets by Alastair Stewart a well known British journalist who is a newsreader on ITV.

Alastair Stewart  @alstewitn 19 Aug
#ragwort Professor Knottenbelt is right. There are more than enough other plants for insects to feed on. Ragwort,however, kills horses.

And in response to Dutch ragwort expert and horse enthusiast Esther Hegt

Alastair Stewart  @alstewitn 19 Aug
@Ragwort_horses He is right that Ragwort kills horses. Insects can feast elsewhere or evolve. Dead horses can't.

I have decided to write an open letter.

Dear Mr Stewart,
I have great respect for you as a journalist but I think that , on the basis of the evidence, that you are wrong.

The evidence very very clearly shows that the risk to horses from ragwort has been exaggerated beyond all reason and I believe since I follow the scientific method and use evidence that I can establish this clearly.

I would first of all recommend that you listen to Esther Hegt. She is a keen and devoted horsewoman from The Netherlands, a highly intelligent and technically minded woman who at first agreed with you, but after looking into the science she realised that the stories which had spread to her country from the UK were wrong.

 I hope that being a successful man in your field who has already shown signs on twitter of being open minded that you will hear me out and listen to what I have to say.

First of all let me deal with the subject of Professor Knottenbelt. It is important to realise that being a professor doesn't give him some kind of divine right to be correct in matters of science. In science it is the evidence that shows who is right. It seems very clear to me, after spending over a decade of detailed study, that he is very clearly wrong.

Professor Knottenbelt has played a pivotal role in this subject. I could choose many many instances of him being quoted in the press to make my point, but I am mainly going to concentrate on examples where we can be certain that he has been directly involved in writing the statements concerned.

One of those sources is a letter that he wrote to the Yorkshire Post about Ragwort  Jacobaea vulgaris (The old name is Senecio jacobaea). He said some rather strange things.

    In one circumstance in Africa where ragwort infusions were fed to humans as herbal remedies, the toll was very heavy.

    A very high number of cases of hepatic carcinoma were reported as well as extensive veno-occlusive disease and liver failure. The plant is toxic to people make no mistake. For example, cereals contaminated with ragwort in Uzbekistan were responsible for large numbers of cases of severe liver disease.

And later.

      In South Africa the plant is causing massive concerns.  

 This sounds very scary but I have checked these statements out. The alkaloids occur in thousands of different plants, 3% of all flowering plants in fact. It is doubtful that the plant grows anywhere in Africa except possibly the in the northern or Mediterranean coast area.  According to my extensive literature searches which reveal that all the poisoning cases are well documented, the known cases in both Africa and Kazakhstan were not caused plant in question, and the Kazakhstan cases were plants in a different botanical family altogether!

As for his comments specifically about South Africa, I have asked around the international network of ragwort experts that I am in contact with. The South African organisation that maintains records of their flora,  have no record of the plant ever being found there.  It seems that it clearly cannot be causing "massive concerns."

In the letter he says very odd things about ragwort's distribution.

    "It has taken over fragile eco-systems on the west coast and islands of Scotland, it has spread across the hills of Wales and the Downs of England."

This is baffling to ecologists who know the plant was always there and hasn't changed in distribution or spread to new parts of the country as he seems to imply. There is however,  a known psychological effect called, "The Bader Meinhoff Effect"  where people think something has become more abundant just because it is drawn to their attention.

Back in 2000 he wrote on the same theme in a conference paper,“Over the last 5 years there has been an explosion of ragwort in the UK."
He always seems to say it is increasing but we have pretty solid evidence that during that period ragwort was actually markedly declining.  There was an official government scientific survey. I don't quote figures or pass stuff on as the real  research data figures were supplied to me as a courtesy, but they would be available I presume to anyone under the Freedom of Information Act.

In that letter Professor Knottenbelt uses a peculiar  and seemingly entirely  wrong statistical method to derive the number of horse deaths. To explain it imagine an opinion poll to decide the way the voting was going for an election and then imagine that the survey was conducted exclusively in the local headquarters of one of the political parties. Do you imagine that you would want, as a journalist, to rely on such a survey? It is obviously not based on a representative sample.

To me Professor Knottenbelt's methodology is very similar. He takes a tiny number of cases from his hospital. where after establishing himself as an expert they are going to be especially highly concentrated and common and tries to extrapolate. You cannot do this as the sample is not representative of the UK's horse population. What is also puzzling and seemingly significant is that he says he gets "more than 10 per year" cases in the Yorkshire Post letter. I have done a Freedom of Information  request to his hospital. They told me me that over the 5 year period 2006-2011 which includes the time of his letter, they recorded no cases at all of ragwort poisoning in horses, NOT ONE!

It seems to me that the professor is rather too keen to exaggerate the problems of ragwort and the frightening tales he tells are open to question.

Now let me  turn to the subject of evolution. I will try to be brief and not quote technical papers although I do have them. These alkaloids are very common. Any grazing animal is going to encounter them in a variety of plants in nature and it is very very clear from the data that the level of resistance is proportional to the likelihood of them being in the diet. The mechanisms here are many and complex, special taste senses, digestive bacteria, different enzymes etc. A horse, just like any grazing animal, is going to have evolved enough resistance to cope with normal life and that is the conclusion that the science supports. If you actually at the published cases of horse poisonings, where it is confirmed as ragwort, which most liver cases aren't, where the circumstances can be established, it is always, it seems, either starvation abuse where the evolutionary drive is going to be,"if you are going to die it is worth trying anything", and when ragwort occurs in quantities in the artificial man-made product of hay. Horses have already evolved a tolerance to ragwort growing in normal  circumstances.

At this point I was going to explain why it seems to me that Professor Knottenbelt is wrong on the toxicology and why it seems very clear that ragwort is not always a cumulative poison but it is too technical and long-winded so you can read it here if you wish Professor Derek Knottenbelt an analysis of his conference paper 2000

Now we come to the insects. I don't think I need to say very much about this. Professor Knottenbelt is obviously a  veterinary expert,  but he is not an expert on insects and he is simply wrong. There are many species dependant on the plant. Evolution is a long process so they simply cannot move to other things.

It is also important as a nectar source for many others and I could give you a long detailed and technical explanation why over zealous ragwort control is a severe problem, but I think it is unnecessary.

Finally. two resources for you ,a detailed set of RagwortMyths , and the original of that letter in the Yorkshire Post. ( You need to scroll down.)







I hope now that you understand why your tweets caused the responses you got.

Yours faithfully,
Neil Jones