First, consider whether this can be done using non-chemical means such as digging out and where this is not feasible, chemical controls may need to be used.
The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.
Non-chemical options are limited. Cutting at the early flower stage reduces seed production but can stimulate the growth of sideshoots, resulting in more vigorous growth in the following year. Cut plants are a serious risk to grazing animals and may still set seed. They should be removed and burnt.
Pulling is practical where weed numbers are low, but the benefit is only temporary. Roots remaining in the soil will give rise to new plants.
Glyphosate (e.g. Roundup Ultra, SBM Job done Tough Weedkiller (soluble sachet only), Doff Advanced Concentrated Weedkiller or Westland Resolva Pro Xtra Tough Concentrate; or for spot treatment use Roundup Gel) can be used to clear small infestations but apply carefully as it will kill any green plants it comes into contact with.
Lawn and grassland weedkillers
In more heavily infested grassed areas, MCPA and 2,4-D (Vitax LawnClear 2) are selective weedkillers that are effective against ragwort when applied at the higher rates mentioned on the product label. These weedkillers are also effective on other broad-leaved plants such as clover.
In rough grass use a selective weedkiller which contains triclopyr (SBK Brushwood Killer) as this would leave the grass unharmed. However, other broad-leaved plants will be damaged (e.g. wildflowers) and so should only be used in grass where such action is acceptable. For garden use only, consider using triclpyr (Vitax SBK Brushwood Killer) in rough grassed areas and lawn weedkillers for lawns.
To control mature plants in pastures apply weedkillers in late April or May. Grazing is not safe for at least four to six weeks after spraying as treated plants remain poisonous. Allow plenty of time for the weeds to decay. Established plants are less susceptible to spraying, particularly after the stem elongates in early June. Spraying from September to November during mild and settled weather will control summer seedlings.
Spraying has to be a routine procedure every autumn, or every second spring, as ragwort seeds remain viable in the soil for up to 15 years. Weedkillers temporarily increase the attractiveness of ragwort to grazing stock, so to be sure of preventing poisoning, keep animals off sprayed pastures until the weed has disintegrated and disappeared.
Weedkillers suitable for large-scale pasture use are available only to qualified professionals. Contact agricultural contractors to treat paddocks and similar areas (see the National Association of Agricultural Contractors). For garden use only, consider using triclpyr (Vitax SBK Brushwood Killer) in rough grassed areas and lawn weedkillers for lawns.
Inclusion of a weedkiller product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener.
Weedkillers for gardeners (Adobe Acrobat pdf document outlining weedkillers available to gardeners; see sections 1a and b, and 4)
Chemicals: using a sprayer
Chemicals: using safely and effectively
Chemicals: using spot and broad-scale weedkillers
Weeds: non-chemical control