Ragwort is a biennial that produces a flat rosette of leaves in its first year of growth that rarely flowers. The flowering head appears in the second year and having set seed will normally die. So what kills ragwort is to prevent it producing seed thus effectively depleting the reserves in its roots. Topping/cutting to stop plants flowering maintains reserves in the roots and encourages the plant to survive for another year and then flower ie it encourages the plant to be perennial rather than biennial.
It is extremely risky to conserve any field containing ragwort plants. Where there are plants they must be dug out and removed before the grass is cut. Where infestations are too high the field should be sprayed in late April – late May when second year plants are at the rosette stage and new seedlings have emerged. However conservation or grazing cannot be undertaken for at least a month after spraying to allow the dead ragwort to rot away. For suitable herbicides etc contact your local consultant.
With low populations spot treatment with citronella oil can be used and is much quicker acting than other herbicides, especially in the spring. Low populations can also be treated with a weed wiper applicator using glyphosate at stem extension up to the start of flowering. However this is relatively slow acting, does not kill new seedlings and it takes a while for the plants to rot away, delaying the restart of grazing.
Sign up to the FAS newsletter
Receive updates on news, events and publications from Scotland’s Farm Advisory Service