Ragwort

Scientific name: Jacobaea vulgaris

Ragwort flower

Ragwort plant

Ragwort seeds

Ragwort before flowering
  • Key characteristics
  • Biology
  • Impacts
  • Control
  • Further information

  • Ragwort has characteristic bright yellow flowers, visible from a great distance in summer
  • Biennial or perennial with a fibrous root system
  • Forms a dense rosette of dark green, deeply dissected leaves, each with a large blunt terminal lobe, in its first year
  • Second year produces a flower stem up to 1.2 m high
  • A compact flat-topped inflorescence composed of about 12 composite flowers, each about 2cm across, appears between November and April
  • Leaves on the flower stem are also deeply dissected and have no stalks, instead clasping the main stem. They do not have a large terminal lobe
  • Plants have an unpleasant smell when crushed.

Origin

  • Ragwort originated from Europe, Asia and Siberia and has become a serious weed in North America, Australia and New Zealand. It was first recorded in New Zealand in the South Island (Dunedin) in 1874
  • Occurs throughout New Zealand in beef cattle and dairy pastures, but also in open forest, swampy areas, along roadsides, railways and along riverbeds. It can become prevalent in conservation areas and national parks. It is also found in the Chatham Islands. Ragwort is more common in higher rainfall areas (> 870 mm)
  • Often found on lighter soils and does not grow as well on heavier soils. It appears to adapt to a wide pH range.

Lifecycle

  • A ragwort plant can produce over 50,000 seeds, some of which can last for up to 20 years in the soil (see references listed under ‘further information’)
  • Most seeds are only spread short distances by the wind, and fall within 15 m of the parent plant, although a few may be carried kilometres. Ragwort plants found in the Southern Alps near Arthurs Pass were thought to have originated from seed blown by strong nor’westers from Westland
  • Seeds germinate in winter or early spring, often in bare areas. Most seeds germinate in the year after their production. However, mortality of seedlings and young plants is high, with few surviving to produce flowers. At three North Island sites 80% of seedlings died each year before flowering
  • Prefers a sunny location for establishment and optimal growth. Seeds germinate faster if covered by a thin layer of soil than if left on the soil surface. Germination is lower in the presence of other vegetation, and dry summers reduce seedling establishment
  • After germination the plant forms a rosette which grows through winter and spring. In its second year, it ‘bolts’ to produce an upright flower stem which branches towards the top and forms the characteristic flat-topped cluster of bright yellow flowers. After flowering plants usually die
  • Ragwort doesn’t just grow from seeds. New shoots can also grow from root fragments left in the soil when the plants are pulled out
  • If ragwort plants have been grazed, cut or damaged so that flowering is prevented, they can produce new buds from the crown or send up new shoots from the roots. In this way ragwort can become a perennial plant
  • Ragwort is subject to Pest Plant Management Strategies in most regions of NZ. Details are available from individual regional councils or unitary authorities. It has been regarded as a noxious plant in NZ since 1900.

Benefits

  • While ragwort is a serious weed of pastures it has some benefits. Flowers provide food for small wasps, butterflies and other insects and seeds provide food for birds. Despite it being poisonous to humans, it has been used historically as a herbal medicine.

  • Alkaloid compounds in ragwort are poisonous and damage the liver of horses and cattle. The compounds are less dangerous for sheep as they are generally broken down by bacteria in the rumen, although long-term exposure of sheep to ragwort can still cause symptoms that can be mistaken for those of facial eczema
  • Older sheep are better than younger sheep in controlling ragwort, because they are more tolerant of the toxin and tend to eat the crown and growing points of the rosette, while younger sheep generally feed entirely on the younger leaves
  • The plant is more palatable and has fewer poisonous alkaloids at the rosette stage than in full bloom. Sheep may even gain a preference for ragwort after they have acquired a taste for it
  • Ragwort may also be toxic to deer
  • The toxic alkaloids cause milk and honey taint
  • It has been estimated that ragwort causes losses to the Australian dairy industry of more than 4 million dollars per year (see references listed under ‘further information’).

Grazing management

  • Ragwort can be grazed by sheep or goats. However, cattle rarely eat ragwort seedlings or rosettes
  • Damage to pasture cover or soil disturbance increases ragwort seed germination
  • Continuous grazing, as opposed to rotational grazing, is more likely to lead to ragwort infestations. Under continuous stocking livestock can graze selectively which can lead to overgrazing and ragwort establishment
  • Once the seedling has formed a rosette, it competes well with grasses and clovers. At this stage, only tall pastures such as a hay crop may reduce its growth.

Pasture species/cultivars

  • Maintaining a dense, vigorous pasture can help prevent ragwort germination and establishment
  • This can be helped by appropriate stocking rates, irrigation and fertiliser
  • Superphosphate and urea applications have both been shown to increase pasture growth and suppress ragwort.

Chemical control

  • Young plants in the rosette stage are easier to control than older plants
  • 2,4-D is more effective on younger than older plants (including older rosettes, budding or flowering plants)
  • 2,4-D and MCPA damage clover. Some products used to control ragwort also damage grasses
  • Check regarding withholding periods for the chemicals used. There may be a withholding period of up to several weeks before stock are allowed back onto the pasture
  • Chemicals that can be used include: 2,4-D, dicamba, triclopyr/picloram, metsulfuron, picloram, MCPA and glyphosate.

ALWAYS READ PRODUCT LABELS BEFORE APPLYING

Active ingredient When to apply Residual effect Grass damage Clover damage
2,4-D Up to small rosette Slight No Slight
dicamba Up to large rosette Severe No Severe
triclopyr/picloram Up to large rosette Yes No Severe
metsulfuron-methyl Up to large rosette Yes Moderate Severe
picloram Up to large rosette Yes No Severe
MCPA Up to small rosette Moderate No Slight
glyphosate Any stage No Severe Severe
aminopyralid Up to large rosette Severe No Severe
clopyralid Up to large rosette Severe No Moderate – severe
thifensulfuron-methyl Up to small rosette Slight Slight Moderate
mecoprop/dichloroprop/MCPA Up to small rosette Yes No Severe

Consult your farm consultant, industry rep or New Zealand Agrichemical Manual for more information about chemical control.

Mowing or grubbing

  • Small patches of plants can be removed by hand or grubbing. However, plants can re-grow from root fragments left in the ground
  • Pulled plants should be removed and burned so viable seed does not spread
  • Larger plants have deep root systems, making it hard to remove all the roots. However, as plants get older, re-growth from root segments is less likely
  • If plants are mown, they can re-grow and produce multi-crowned plants, each crown with stems. This may prolong the life of the plant and turn it from a biennial to a perennial
  • Mowing or cutting repeatedly, in combination with appropriate fertilisers, can favour grass growth and help prevent ragwort from establishing.

Ploughing

  • For large infestations, deep ploughing, followed by summer and autumn cultivations, can kill ragwort plants, re-growth and seedlings.

Integrated pest management

  • Older plants may be hard to kill. However, one technique is to leave them to die naturally in ungrazed areas, followed by grazing, spot-spraying and maintaining a dense pasture to control the seedlings.

Biocontrol

  • In recent years the combined effects of biocontrol agents have significantly reduced the incidence of ragwort in most areas.

Cinnabar moth (Tyria jacobaeae)

  • Cinnabar moths were first established in New Zealand in the 1939s, but only became well established in the southern North Island. In the 1980s moths from there were multiplied and released throughout the country
  • Cinnabar moths have now established throughout the country but distribution is patchy. However, populations seem to be growing
  • Moths are about 2 cm long with red and brownish-black markings. Cinnabar moth caterpillars vary in the damage they cause to ragwort plants, sometimes being severe in their effects and sometimes less so. They become brightly coloured as they get older, with smooth, bold, yellow-and-black stripes.

Ragwort flea beetle (Longitarsus jacobaeae)

  • Ragwort flea beetle was first released in the late 1980s and early 1990s, is now well-established throughout the country and has contributed strongly to the decline of ragwort in New Zealand
  • Small (2.5–3.8 mm long) golden-brown adults have large hind legs that allow them, when disturbed, to leap 1 m. Larvae are white and feed on the roots, inside the crown, and within the leaf petioles
  • Heavily-infested plants die and, if plants survive they produce fewer flower stems
  • The cinnabar moth and the ragwort flea beetle are complementary: cinnabar moth larvae feed on ragwort flowers and leaves in summer and flea larvae feed on the roots, crown and leaf stalks during the rest of the year.

Other biocontrol agents

  • Ragwort seedfly (Botanophila jacobaeae) was released in the late 1930s, but only established in the Central North Island and has not spread further. The adults are small grey flies and the white larvae feed inside the flower heads, reducing seed production in early flowers but their impact is less later in the season
  • Ragwort stem and crown boring moth (Cochylis atricapitana) was introduced to the West Coast from Australia in 2005 because other agents seemed not so effective there. Caterpillars mine into the leaves and then into the stem, causing stems to thicken and leaves to bunch up. It has not yet established, so as yet it has had no effects
  • Similarly, ragwort plume moth (Platyptilia isodactyla) was introduced to the West Coast in 2005. Again it is too soon to see any effects on ragwort populations.

  • Hayes LM 2005. Biological control agents for weeds in New Zealand: A field guide. Landcare Research New Zealand Ltd. (accessed 30 July 2014).
  • Leiss KA 2011. Management practices for control of ragwort species. Phytochemistry Reviews 10: 153-163.
  • Popay I, Champion P, James T 2010. An illustrated guide to common weeds of New Zealand. New Zealand Plant Protection Society, Christchurch, New Zealand. 416 p.
  • Richardson F J, Richardson RG, Shepherd RCH 2006. Weeds of the South-East. An identification guide for Australia. RG. and FJ Richardson, Meredith, Victoria, Australia
  • Wardle DA 1987. The ecology of ragwort (Senecio jacobaea L.) – a review. New Zealand Journal of Ecology 10: 67-76.
  • Young S 2013. New Zealand Novachem agrichemical manual. Agrimedia Ltd., Christchurch, New Zealand. 767 p.
  • Weedbusters NZ, 2016, Jacobaea vulgaris factsheet (accessed 17 October 2016)