In 1753, Carolus Linnaeus described tansy ragwort, Senecio jacobaea, in Species Plantarum (2). This species is a member of the largest genus of the sunflower family (Asteraceae), which encompasses 1300 genera and 21000 species worldwide (8). Taxa in the genus Senecio L. range from herbs to shrubs and occur globally. Comparatively few senecios are of economic importance and many of them are weeds (14), among them tansy ragwort, which can infest pastures, crowding out more desirable forage and poisoning grazing livestock (10).
The generic name Senecio is derived from the Latin senex meaning old or old man, the pappus resembling a white beard (19). The species name is from jacobaeus, the Latin word for St. James (Jacobus) (7). The word ragwort probably refers to the ragged form of the leaves; the term entered the English language in 1450 (15). In 1597, Herarde wrote in his Herbal: "The country people call it ragworte ... also ragwoort ... it groweth everywhere in untilled pastures and fields" (15).
Tansy ragwort, an erect, robust biennial or short-lived perennial, develops a stout rootstock from which grow numerous rather fleshy roots extending to a 30-cm depth. Under ideal conditions, the plant may attain a height of 1.75 m (14). Its comparatively large size and prominently dissected leaves distinguish tansy ragwort from other North American senecios (4, 14). The lower leaves, 7 to 20 cm long and 2 to 6 cm wide, form a rosette which commonly reaches a diameter of 0.5 m and dies back when flowering is well advanced (14). The upper part of the stem is much branched and from June to November bears up to 2500 numerous, bright golden yellow flowers in 20- to 60-headed, flat-topped corymbs (11, 14); both ray and disc florets are produced. Numerous kinds of insects effect pollination (14). Plants produce dimorphic achenes; those from ray florets are glabrous, while those of disc florets are pubescent along prominent ribs. A pappus 6.25 mm long is attached to the top of the achene (14).
In his herbal, Gerard (6) noted that tansy ragwort was known in ". . . Latin as Herba St. Jacobi and in English, St. James his wort." He added, "The countrey people doe call it stagger-wort, and staner-wort, and also rag-wort, and ragweed." The plant's other names include ". . . flos Sancti Jacobi, or St. James Wort, benweed, curly doddies, stammerwort (it was prescribed for speech impediments), stinking nanny, dog standard and cankerwort." This last name refers to its use in treatment "of running sores-cankers-and cancerous ulcers."
Other common English names include stavewort, kettle-dock, felonweed, Fairies' horse (2), and stinking willy, once a widely used name for the plant in the U.S. (1).
Tansy ragwort, a widespread native of Europe and western Asia, including Siberia, generally occurs in unthrifty pastures, in waste areas and along roadsides in cool, high rainfall regions (1, 5). It is now extensively naturalized in many temperate regions, e.g., northwest India, Africa, U.S., Canada, Argentina, Australia, and New Zealand (11, 14). Ragwort was initially recorded in New Zealand in 1874 and was declared a noxious weed in 1900; it is now found in nearly every county (14).
Tansy ragwort was introduced into North America early on, and was observed in Canada in the 1850's (1). From the beginning, it was a troublesome weed that spread rapidly (14). By 1898, ragwort was reported in waste places in Nova Scotia, New Brunswick, and Ontario, and in ballast around New York and Philadelphia (2). It spread along the Atlantic Coast from Maine to Rhode Island (17). Now it has become established along the Pacific Coast in British Columbia, Washington, Oregon, and northern California (13, 17), and since the mid 1950's has become an important weed there (13). Tansy ragwort was introduced to western Oregon in the late 1800's, and within 50 yr became the region's most noxious weed (18). Estimated losses associated with it are as high as $10 million annually (1, 13).
Tansy ragwort was extensively prescribed in medieval medicine (3, 11). Noted Gerard: "It is much commended, and not without cause, to helpe old aches and paines in the armes, hips, and legs, boiled in hog's grease to the forme of an ointment. Moreover, a decoction [of it] is much set by as a remedy against swellings and abscesses of the throat, which it wasteth away and thoroughly healeth . . ." (6). Decoctions were also prescribed for their detergent and diaphoretic effects, for treatment of coughs, colds, and catarrh, and for application to ulcers, sores, and wounds (10).
Tansy ragwort is important economically because various alkaloids in its foliage make it poisonous to livestock (1, 11). The plant contains pyrrolizidine alkaloids which are toxic to cattle, deer, horses, and goats; sheep are less affected. Although cattle do not generally graze it directly, the alkaloids are still toxic in hay and silage (1). The alkaloids cause degradation of liver function, usually with lethal results. And the alkaloids have other detrimental effects as well. Ragwort consumption rapidly reduces butterfat production in cattle, and the honey produced by bees that have gathered ragwort pollen is tainted, being too bitter and off-color to market (1).
In Wales in the early 1800's, a horse disease loosely termed `stomach staggers' was recognized and associated with tansy ragwort. In the Western Hemisphere, Pictou disease of cattle surfaced in Nova Scotia before 1860 and caused serious losses. Likewise, it was associated with tansy ragwort. Only in 1902 was it discovered that Winton disease of horses and cattle in New Zealand was caused by ragwort ingestion (9).
In other parts of the world, diseases causing characteristic and similar liver lesions emerged, e.g., in South Africa, the Molteno disease of cattle and dunziekte of horses; and in Norway, sirasyke (9).
In Australia, ragwort poisoning of cattle is uncommon, probably because the plant is not sufficiently abundant except in a few areas. In contrast, ragwort is common in New Zealand where it is a major cause of plant poisoning in cattle. Unless they are very hungry, animals rarely consume enough ragwort to induce liver damage (5).
Sufficient rainfall and the presence of medium to light soil types are the main ecological factors governing the distribution of tansy ragwort. The plant is not adapted to heavy clay soils because seedlings become desiccated in the topsoil during prolonged dry spells. Sheep and dairy farming also favor the plant's growth (14).
Grazing or mowing tansy ragwort usually converts it into a perennial with a multiple crown and many flowering stems. Flower heads average 55 achenes, giving an approximate range of 50 000 to 150 000 achenes per plant over 4 to 6 wk (14). After pollination, the achenes ripen in about 7 to 10 d. Achenes produced on the lower branches are on average heavier and have higher germination rates than those produced on the tops.
The achenes possess different dormancy and dispersal characters, enabling the plant to establish in a wide range of habitats (1). However, wind dissemination is not as effective as is popularly supposed (14). A heavy infestation of ragwort spreads mainly in the direction of the prevailing wind and then largely by marginal spread. The vast majority of seed is deposited within 10 m of the original infestation (14). The germination rate is 50 to 86% under suitable conditions. However, burying the achenes with 15 cm of soil prevents germination (14).
Vegetative reproduction is common, especially after damage to the plant. When the plant's numerous root and stem adventitious buds are fragmented, they initiate growth (1).
GRAZING AS A CONTROL
Young tansy ragwort plants are willingly grazed by sheep, which may eat it daily without suffering any ill effects. Intensive grazing is the chief way of eradicating the weed, especially in New Zealand. Wrote Long in 1910, "On land regularly stocked with sheep not a single ragwort can be seen." Maturing plants, about flowering time, are tough and hard (10).
As sheep forage, the plant exceeds standard nutrient requirements for both protein and digestibility (16). In New Zealand, plowing the infested land to produce winter crops gives newly sown pastures a respite of 2 to 3 yr before ragwort is likely to reappear in any quantity (14).
CLASSICAL BIOLOGICAL CONTROL
The first biological program against tansy ragwort was begun in the late 1950's by the USDA's Agriculture Research Service in Albany, CA. By that time, many European insect predators of tansy ragwort were already known, including the cinnabar moth (Tyria jacobaeae L.) and seedhead fly (Pegohylemyia seneciella Meade), which already had been introduced into Australia and New Zealand (13). The cinnabar moth, whose larvae feed on ragwort foliage and flowers, was the first insect released into North America for biological control of tansy ragwort. By 1960, the cinnabar moth had become established. Since additional control was needed, the seedhead fly, whose larvae feed on developing ragwort seeds, was released in 1966. A third insect, the root feeding flea beetle (Longitar-susjacobaeae Waterhouse), was released in the late 1960's. Its larvae feed on ragwort root crowns, stems, and leaf petioles during late autumn, winter, and spring (13).
By 1976, the excellent complementary actions of the cinnabar moth and the flea beetle had successfully brought ragwort under biological control in the Ft. Bragg, CA area. Both insects still persist at the control sites despite very low numbers of ragwort plants. The plant's natural enemies appear to have reached an equilibrium in which each regulates the other's population to low numbers. and densities. Its control has resulted in the return of near natural vegetation to thesite (13).
Equally successful is the biological control of ragwort in Oregon. Following the introduction of the three natural insect enemies used in California, ragwort declined to < 1 % of its former abundance and was replaced by a plant community composed predominantly of introduced perennial grasses. In the western part of the state, a ragwort infestation estimated at > 12 000 km in 1976 had declined 60 to 90% by 1988. However, the long-term dynamics of ragwort may be influenced by the presence of a large persistent seed bank which is invulnerable to the natural enemies (12).
1. Bain, J. F. 1991. The biology of Canadian weeds. 96. Senecio jacobaea L. Can. J. Plant Sci. 71:127-140.
2. Britton, N. L. and A. Brown. 1898. An Illustrated Flora of the Northern United States, Canada and the British Possessions. Volume 3. Charles Scribner's Sons, New York.
3. Culpeper, N. 1802. Culpeper's Herbal or The Complete English Family Physician, with additions by G. A. Gordon. Hogg and Co., London. 416 p.
4. Darlington, W 1859. American Weeds and Useful Plants. Orange Judd &Company, New York. 458 p.
5. Everist, S. L. 1981. Poisonous Plants of Australia. Angus & Robertson Publishers, Sydney. 966 p.
6. Gerard, J. 1928. Gerard's Herbal. Houghton Mifflin Co., Boston. 69 p.
7. Gledhill, D. 1989. The Names of Plants. 2nd Ed. Cambridge University Press, Cambridge. 202 p.
8. Hickman, J. C. 1993. The Jepson Manual, Higher Plants of California. University of California Press, Berkeley. 1400 p.
9. Kingsbury, J. M. 1964. Poisonous Plants of the United States and Canada. Prentice-Hall, Inc., Englewood Cliffs, NJ. 626 p.
10. LeStrange, R. 1977. A History of Herbal Plants. Angus and Robertson, Publishers, London. 304 p.
11. Long, H. C. 1910. Common Weeds of the Farm and Garden. Frederick A. Stokes Co., New York. 451 p.
12. McEvoy, P., C. Cox, and E. Coombs. 1991. Successful biological control of ragwort, Senecio jacobaea, by introduced insects in Oregon. Ecol. Applications 1:430-442.
13. Pemberton, R. W. and C. E. Turner. 1990. Biological control of Senecio jacobaea in northern California, an enduring success. Entomophaga 35:71-77.
14. Poole, A. L. and D. Cairns. 1940. Botanical aspects of ragwort (Senecio jacobaea L.) control. New Zealand Dep. of Sci. Ind. Res., Bull. No. 82. Wellington. 61 p.
15. Simpson, J. A. and E.S.C. Weiner. 1989. The Oxford English Dictionary, 2nd Ed. Clarendon Press, Oxford.
16. Sharrow, S. H. and W. D. Mosher. 1982. Sheep as a biological control agent for tansy ragwort. J. Range Manage. 35:480-482.
17. United Stated Department of Agriculture. 1970. Selected Weeds of the United States. Agriculture Handbook No. 366. 463 p.
18. United States Department of the Interior. 1994. Noxious Weed Strategy for Oregon/Washington. Oregon State Office,Portland.
19. Zimdahl, R. L. 1989. Weeds and Words. Iowa State University Press, Ames. 125 p.