T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Jacobaea vulgaris (Yellow Ragwort)

Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Asterales
Family: Asteraceae
Subfamily: Asteroideae
Tribe: Senecioneae
Genus: Jacobaea
Binomial name: Jacobaea vulgaris
Formerly: Senecio jacobaea
Common name: Ragwort

Jacobaea vulgaris (Ragwort) was introduced into  New Zealand in 1870 in contaminated seed  (Syrett  1983) reaching epidemic proportions during the intensive dairying practices of the 1920s  and  30s.  Ragwort is a problem on dairy and deer farms because cattle and deer do not eat ragwort, and if they do, its toxic alkaloids  can cause liver damage. 
Jacobaea vulgarisis a noxious weed It is a rosette-based, robust biennial or perennial with a characteristic unpleasant smell when bruised. Leaves dissected into large lobes.
The flower stems are up to 1.2 m tall, bearing bright yellow composite flowers, each 2 cm across, in flat-topped clusters. The flowers are golden-yellow, about 2 cm in diameter, with golden-yellow disk florets, and about twelve yellow ray florets, in compact flat-topped terminal inflorescences. It flowers Nov-Apr and the fruit is rounded achenes about 2 mm long, with a pappus of simple hairs up to 5 mm long.
The leaves are a rosette of dark green, pinnately lobed leaves 4-8 cm long with large blunt terminal lobes. The stem leaves are deeply cut, stalkless, clasping the stem, with no broad terminal lobes. Leaves often with purple colouring on the underside. Stems are leafy and branching up to 50-120 cm tall.
Pollination is by a wide range of bees, flies and moths and butterflies. Over a season, one plant may produce 2,000 to 2,500 yellow flowers in 20 to 60 headed, flat-topped corymbs. The number of seeds produced may be as large as 75,000 to 250,000: these can lie dormant in the soil for up to 16 years.  
The plant forms a rosette in its first year, and usually flowers and then dies in its second year unless its growth is interfered with when it can become a multi-crowned perennial.
It is poisonous to cattle and horses, but less so to sheep. Usually ignored by cattle and horses but kept in check by sheep. The poison affects the liver, can be very slow acting in sheep and its effects can be confused with those of facial eczema.
During 1930 to the 1950s attempts to control ragwort sodium chlorate (a white crystalline solid) was commonly was used. The plant's stem was cut at ground level and a handful of sodium chlorate was dropped onto the stump. A problem developed with this chemical because when combined with organic material, such as cotton and woollen fibres, the mixture becomes violently explosive. One farmer Richard Buckley was lucky when his trousers blew up when he wasn’t wearing them. He was badly shocked, but as the Hawera Star reported on 12 August 1931, his quick thinking saved him from serious injury. “While Mr Richard Buckley’s trousers were drying before the fire recently, they exploded with a loud report. Although partially stunned by the force of the explosion, he had sufficient presence of mind to seize the garments and hurled them from the house, where they smouldered on the lawn with a series of minor detonations.”
Similar reports came in from other parts of the country. One individual was shocked to observe a newly hung-out load of washing burst into flame on the clothesline. Farmworkers discovered for the first time that smoking could be hazardous to their health, as items of their clothing lit up when they were smoking.
Longitarsus jacobaeae is a species of flea beetle known as the Tansy ragwort flea beetle was introduced as a biological control. The beetle is most effective when used in conjunction with the cinnabar moth (Tyria jacobaeae), another ragwort biocontrol agent.

This is a photo showing how invasive Jacobaea vulgaris can be on farmland. The photo was taken in the Buller area 

Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0/