Professor Derek Knottenbelt is a well known veterinary expert. He is well known for his campaigning against ragwort.

In the Autumn 2002 Edition of the Newsletter of the Friends of Bidston Hill Professor Derek Knottenbelt wrote an article on ragwort

These are some significant quotes from the article followed by rebuttals correcting any errors.

"Death from liver failure is an extremely distressing affair in horses, cattle and sheep. There is also a small but important risk to humans in that the toxin has been found in honey and in milk and it is known that the toxin is poisonous to humans as well."

It is quite true that the plant, like many, is poisonous to humans , but this only occurs if you eat this bitter plant. In fact there is a close relative with the same poisons planted in parks and gardens regularly all over the UK. An extensive search of the literature shows fails to find that there has ever been a recorded example of someone being poisoned by either plant in the UK.

"The toxin can also be absorbed through the hands if the plant is handled."

There are several briefings on this matter on this website. Investigations by Esther Hegt, a Dutch Ragwort expert and Dr Pieter Pelser from New Zealand who is a world leading expert with a PhD on ragwort say that Professor Knottenbelt does not have proper evidence for this claim and that it is not supported by the biochemistry. See Ragwort Humans

"Although there are no horses, cattle and sheep grazing on the hill, the weed will quickly seed and take over and then it will become a source of poison for animals and humans in our general area."

Ecological studies of ragwort (Cameron 1935) show that this does not happen as ragwort needs bare ground to germinate. Also we know from studies of the behaviour of the seeds (See Ragwort Seed dispersal ) that the seeds do not usually spread long distances.

“The council has a legal obligation (under the Injurious Weeds Act 1956) to remove all Ragwort from their land (or risk prosecution by DEFRA) but we are well aware that they do not have either the will or the resources to do this and we are left with having to do it for them unless we want the hill overtaken by this disgusting weed. “

Firstly he has the name and date of the act of parliament wrong it is the Weeds Act 1959 not the Injurious Weeds Act 1956, but most importantly he has the meaning of the law wrong. What he says here about the council having a legal obligation under the law to control ragwort is simply untrue. The facts are that in extreme circumstances you may be ordered to control ragwort but without an order there is no legal obligation to do anything. This is a common myth and several companies have been forced to stop making this claim as a result of action by the Advertising Standards Authority. This site has a briefing on Ragwort law.

"It is important at this time of year to remove the entire flowering heads because each plant will produce around 150,000 seeds most of which will germinate next year."

It is not true that each plant will produce around 150,000 seeds. Most plants will produce far far less. In September 2013 a leaflet from the horse charity Redwings was banned by the Advertising Standards Authority for making the claim that each plant produces 150,000 seeds. This is because it was clear that the data showed that this is not the case. This site contains a briefing on ragwort seeds which uses measured figures. Ragwort germination is a complex matter even if it were to be true that most of the seeds would germinate they certainly would not grow into plants. On average in the UK, since government scientific surveys show it is decreasing each parent plant produces less than one new plant in the following season. It would therefore seem that these claims are highly misleading.

References
Cameron E. (1935) Study of the Natural Control of Ragwort (Senecio Jacobaea L.) Journal of Ecology Vol. 23, No. 2 pp. 265-322