Ragwort

Image, thanks to Terry

There is probably no other plant that causes such intense debate. As with everything there’s much misinformation passing as fact.

The big question for us, with conservation as our aim, is how to be a good neighbour and not be a source of seeds but at the same time manage the land for nature.

The Weed Act names it as an ‘injurious weed’ and requires us to prevent it from spreading (1). Ragwort is toxic to Horses, livestock and Humans and probably all vertebrates. The toxin (which becomes a pyrrolizidine alkaloid in the body) can even be detected in honey. They aren’t just confined to Ragwort and are found in many other plants all over the world. Even those used for common herbal teas and herbal remedies. There’s no evidence though that the toxins in honey, herbal teas or remedies are causing a problem for people.

Ragwort is the only food plant of the cinnabar caterpillar, it’s also a good source of nectar for pollinators.

How do we tackle these two seemingly unreconcilable positions?

Ragwort begins to set seed late July and finishes late August. Once it’s finished flowering it’s no value to pollinators. Many of the Cinnabar Moth Caterpillars will also have begun to pupate at ground level by then as well (2). So, by deadheading between end of flowering and before seeding we can allow pollinators to exploit the flowers but can usefully reduce the spread of seeds. The RHS say that 'a single plant is capable of producing 50 - 60,000'. We inspect each Ragwort plant before deadheading to make sure there aren't any Cinnabar Moth Caterpillars. If there are the whole plant is left untouched or the caterpillars are relocated to Ragworts that won’t be cut. Another reason for not deadheading too early is that the Ragwort will produce more flowers. When it’s going to seed the plant dies and won’t produce more flowers.

It would be very time consuming and costly to remove all Ragwort plants from the 20ha always assuming you could find the labour for such a intensive task. Our approach has been to remove the flowering heads closest to our neighbour’s land.

It’s interesting to see that we had hardly any Ragwort growing in a fenced off area of grassland where livestock hasn’t been allowed to graze more than three years. Last winter our field became heavily poached by cattle, which is likely to have significantly contributed to the large amount of Ragwort growing this summer.

DEFRA’s code of practice classifies the risk of Ragwort spreading under three levels: high Risk: within 50m of land used for grazing, medium Risk: 50m to 100m and low Risk: greater than 100m. It qualifies this by saying that ‘the distances given…. are guidelines only’ and that ‘prevailing winds, topography, shelter belts, natural barriers, soil type and vegetation cover of receiving land’ make a difference. No research is referenced so it’s clearly based on guesswork. This is a very sloppy contribution from DEFRA as an actual study was carried out in the USA (3) and found that ‘the majority of [seeds] dispersed very short distances… 31% travelled only 1 m, 89% travelled 5 m or less, and none were collected > 14 m from the source’. Cutting a 100 m strip compared to a 14 m strip would be over twenty times the amount of work.

References

(1) The ‘Weed Act 1959’ s 1(1) says that ‘the occupier of the land…… [is required] to take such action …. to prevent the weeds from spreading’, s 2(1) names Ragwort as a ‘injurious weed’. The Weed Act has been amended by the Ragwort Control Act 2003 which allows the Government (DEFRA) to ‘make a code of practice for the purpose of providing guidance on how to prevent the spread of ragwort’.(1) Deinzer ML, Thomson PA, 1977. Pyrrolizidine Alkaloids: Their Occurrence in Honey from Tansy Ragwort (Senecio jacobaea L.)

(2) The Cinnabar Caterpillars need Ragwort plants to grow but after they've fed on them the Sussex Wildlife Trust say that once the caterpillars have developed, which takes about a month, 'they will descend to ground level ready to pupate. They will remain here all winter, safe inside their cocoons, and complete their metamorphosis the following spring to emerge as beautiful black and red adults.'

(3) McEvoy PB, Cox CS, 1987. Wind Dispersal Distances in Dimorphic Achenes of Ragwort, Senecio Jacobaea