Facts about Ragwort

Description
Tansy Ragwort or Common Ragwort, Senecio jacobaea, is usually considered to be a biennial, over wintering either as seeds or as rosettes, but it is also capable of becoming a perennial through environmental stress or interference by competitors, herbivores, or control tactics.

The plant is erect and robust, ranging from about 1.3 to 6 ft tall, and develops a stout taproot from which grow numerous fleshy roots extending to about 1 ft deep. Leaves are light to dark green and deeply lobed. The lower leaves form a rosette which die back when flowering is well advanced. The upper part of the stem is highly branched and bears up to 250 bright yellow daisy-like flowers. Single plants are capable of producing over 150,000 seeds, which can remain viable in the soil for years.

Damage
This weed contains alkaloids that are toxic to cattle, deer, pigs, horses, and goats. Sheep appear to be less affected, and can consume great quantities without apparent injury. In susceptible animals, the alkaloids cause degradation of liver function, with lethal results in one to two days when the animal ingests three to seven percent of its body weight in Ragwort. However, such acute poisonings seldom occur because the low palatability of the plant usually results in only small quantities being consumed per day. Chronic effects result from a gradual loss of liver function that eventually develops into a cirrhosis-like condition, eventually leading to death.

The alkaloids in Ragwort also rapidly reduce butterfat production in cattle, and taint honey produced by bees such that it is usually too bitter and off-color to market. Although cattle do not generally graze Ragwort directly, the plant's presence in hay often results in the abandonment of the crop.

Distribution
Tansy ragwort is native to Europe, Asia and Siberia, extending north as far as Norway and south into Romania, Hungary, and Bulgaria. It has been introduced into Australia, New Zealand, South Africa, South and North America. In North America it is established in areas with cool, wet, cloudy weather. It was first recorded in California in 1912 and in Oregon in 1922, and by the mid 1950s had become an important weed of the Pacific Coast. It occurs on both coasts, in the east from Newfoundland to New England and in the west from British Columbia to Northern California. Ragwort occurs on many different soil types, particularly on light to medium, well-drained soils. Although Ragwort rarely grows in annually tilled lands, it can invade grasslands, disturbed areas, forests, pastures, and wooded pastures.

Life Cycle
Ragwort is usually a biennial (or short-lived perennial if mowed or grazed), producing a low rosette about 2 to 6 inches in diameter. The flattened rosette overtops and kills the surrounding vegetation, either by allelopathy, light limitation, suffocation, physical suppression, or some or all of these in combination. Rosettes usually overwinter, and produce a flowering stalk in the next growing season (usually summer). Most individual plants die after flowering, creating a gap suitable for immediate colonization by seedlings.

Ragwort reproduces mostly from seed, but regeneration of shoots can occur from crown buds, root fragments, and intact roots. Disturbance or injury promotes vegetative propagation. Roots of rosettes form buds more readily than those of flowering plants. If not timed correctly, grazing or mowing Ragwort can convert it into a perennial with a multiple crown and many flowering stems. Flower heads average approximately 55 achenes (dry fruit bearing a single seed), ranging from 5000 to 200,000 achenes per plant, which ripen in about 7 to 10 days. The seeds possess different germination rates and dormancy and dispersal characters, enabling the plant to establish in a wide range of habitats. The size, dispersal, and dormancy of achenes varies with the position on the head. The central ("disk") achenes are released into the environment shortly after they mature, possess dispersal structures that enable them to be carried by wind or animals away from the parent, and germinate quickly under favorable conditions. The marginal ("ray") achenes are retained by the parent for months, lack dispersal structures, and take approximately twice the time to germinate under favorable conditions.

A heavy infestation of Ragwort spreads mainly in the direction of the prevailing wind, and then largely by marginal spread. Although seeds can be dispersed via water, wind, or spread by people and livestock, the majority of seed is deposited within about 33 ft of the original infestation. The germination rate is 50 to 86% under suitable conditions. However, burying the seeds under about 6 inches of soil prevents germination until the soil is disturbed and brought closer to the surface. Seeds have been shown to have about a 24% viability percentage after 6 years of burial and can remain dormant for as long as 15 years.

Common Types of Ragwort

Ragwort is classified in the division Magnoliophyta, class Magnoliopsida, order Asterales, family Asteraceae (Compositae)

COMMON RAGWORT Senecio jacobaca
An often hairless biennial, 1-4 ft. high, branched only at the top, with deeply pinnately lobed leaves, the lobes toothed and the end one small and blunt. Flower heads in large dense flat-topped terminal clusters, yellow, nearly always rayed, and daisy-like, the rays also yellow, minutely toothed at the tip; outermost sepal-like bracts few, much shorter than the dark-tipped inner.
Fruits of the diskflorets downy, of the ray-florets hairless.

Habitat: Widespread and often abundant in dry sandy or chalky grassland and on dunes.

Flowers: June onwards.

MARSH RAGWORT Senecio aquaticus
Shorter, more widely branched and less stiff than the last species, the glossier leaves mostly with a large end lobe and much smaller forward-pointing side-lobes; root-leaves oval, often undivided. Flower heads much larger, an inch or more across, in broader, looser clusters; all fruits hairless. Autumnal shoots from mutilated plants of Common Ragwort can, however, look very similar, except for the downy fruits of the disk-florets.

Habitat: Widespread and locally frequent in wet meadows.

Flowers: June onwards.

HOARY RAGWORT Senecio erucifolius
Usually narrower, less bushy, more erectly branched and greyer with sparse cottony down than Common Ragwort, with very short creeping runners; smaller, more deeply and narrowly lobed leaves, the end lobe narrow and pointed; smaller, paler yellow, flower-heads; the outer row of sepal-like bracts about half as long as the rest and the fruits all downy.

Habitat: Widespread but local in grassy places in the lowlands, mostly on clay or chalk. In Ireland only round Dublin.

Flowers: July onwards, at its best when most Common Ragwort is over.

OXFORD RAGWORT Senecio squalidas
A branched, straggling annual or perennial, about a foot or so high, more like a short Marsh Ragwort than Common Ragwort, and virtually hairless, with glossy leaves varying from deeply pinnately lobed to undivided, only the lower ones stalked. Flower heads large, yellow, the rays minutely notched but not toothed; sepal-like bracts tipped blackish, the outer row much shorter. Fruits normally all downy.

Habitat: An increasing invader of walls, waysides, railway banks, waste and cultivated ground, though still far from everywhere and very local in the N and Ireland.

Flowers: April onwards.

Toxicity
All parts of Ragwort are poisonous. Stems contain from 25 to 50 percent of the alkaloid concentration found in the leaves, whereas the flowers contain at least twice as much as the leaves. Ragwort contains six different pyrrolizidine alkaloids, which accumulate in the liver. When these compounds are converted in pyrroles, they cause liver damage. Poisoning often occurs when small plants intermixed with desirable forage are ingested accidentally by cattle and horses while grazing. Animals may die after consuming 3 to 7 percent of their body weight in Ragwort.

Ragwort poisoning also is caused by contaminated hay or silage. Stock cannot avoid it in hay or silage, and the poisonous alkaloids are unaffected by drying or ensiling. In silage, the alkaloids diffuse out of the Ragwort and into the surrounding material. Ragwort becomes more attractive to livestock after cutting and wilting or after spraying with herbicides.

Young animals are two to three times more susceptible to Ragwort poisoning than mature animals. Cattle and horses are more susceptible than sheep, llamas, or goats. There is evidence that Ragwort alkaloids may accumulate in milk and cause symptoms in young animals consuming the milk