The first step in an IVM program is to gather information on the life cycle and habits of the noxious weed.
Tansy or common ragwort, Senecio jacobaea, is a weed of the sunflower family Asteracaeae. It is usually considered to be a biennial, overwintering 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 three years or longer. Its comparatively large size and prominently dissected leaves distinguish tansy ragwort from other North American Senecio species (Mitich 1995; Coombs et al. 1991).
In North America, tansy ragwort is a problem weed in pastures, rangelands, and clear-cuts on both the east and west coasts, particularly in Oregon. Ragwort competes with valuable forage species, but it derives its greatest economic importance from the losses it causes to the cattle industry. 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 (Goeger et al. 1981; Giles 1983; Wardle 1987; James et al. 1988; Coombs et al. 1991; Peterson and Culvenor 1983).
The alkaloids in tansy 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 tansy ragwort directly, the plant’s presence in hay often results in the aban-donment of the crop (Miller 1936; Deinzer et al. 1977).
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. Tansy ragwort occurs on many different soil types, particularly on light to medium, well-drained soils. Although tansy ragwort rarely grows in annually tilled lands, it can invade grasslands, disturbed areas, forests, pastures, and wooded pastures. (Gilkey 1957; Harris et al. 1971; Coombs et al. 1997).
Tansy 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 (Ahmed and Wardle 1994; McEvoy 1984; Coombs et al. 1997).
Tansy 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 tansy 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 (Wardle 1987; Poole and Cairns 1940; Cameron 1935; McEvoy 1984; McEvoy 1983).
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 (Schmidl 1972; Thompson and Makepeace 1983; Coombs et al. 1997).
Special Challenges to Management
Attempts to control the weed by hand-pulling, cutting, or the use of herbicides are rarely effective in the long term, due to rapid re-establishment from the seed bank or from persistent rootstocks. In new infestations that are less than 1/10th of an acre, hand pulling can be 50% effective. Longevity studies mentioned above indicate that some ragwort seeds maintain their viability in the soil for as long as 16 years (Paul et al. 1993; Thompson and Makepeace 1983).
Some questions, such as those below, can only be answered on site.
Set Realistic Goals for Your IVM Program
The answers to the following questions can help you set realistic objectives and goals.
Containment - keeping an established population of the weed from spreading to non-infested areas. This strategy is especially useful when time and money are in short supply or when the infestation is very large. For example, a barrier strip between infested and non-infested areas can be maintained and monitored so that adjacent lands remain weed free. In addition, measures that stop seed production will prevent further spread of the weed.
Reduction - reducing the area covered by tansy ragwort, or reducing its dominance. This strategy can also be used against new or established weeds, but it requires more resources and more time than containment.
The "Bradley Method" (see Appendix 2), developed in Australia, is a simple yet innovative strategy for natural areas that combines containment and reduction.
Eradication - completely eliminating the weed from
the management area. This strategy usually consumes the greatest amount
of time and resources and is applicable mainly to newly-invading weeds
that are confined to a limited number of small areas.
Establish Monitoring Programs
When planning a monitoring program, keep in mind the context of your target weed: is it invading or has it already invaded?
Locate and record tansy ragwort infestations on a map. (Chapter 2 of the University of Northern Iowa IVRM Technical Manual contains a detailed discussion on how to map and inventory vegetation - see Bibliography). Note particularly sensitive areas on the map, such as critical habitat for threatened or endangered species, agricultural production areas, or areas subject to frequent disturbance and thus prone to invasion. Update maps at regular intervals.
Focus monitoring efforts on sites where tansy ragwort problems are most likely to occur (see Distribution). Encourage public sighting and reporting through an education or incentive program (see Educate Vegetation Management Personnel and the Public).
Prioritize the sites you will work on. Make a realistic assessment of your weed management resources, keeping in mind the goals of your project and the cost of a follow-up program after any treatments. Without follow-up, your control efforts will be wasted. It is better to thoroughly control a weed at one or two sites than to use up resources to incompletely control the weed at many sites. If the weed is very widespread, try to determine where it poses the most serious economic, social, or environmental problem and concentrate on those areas.
Plan monitoring and treatment efforts to coincide with critical life stages of the weed. To use your resources efficiently, try to include monitoring with other planned activities in the area.
Maintain records of your monitoring activities. Creating standardized forms will make data collection easier and help remind you to gather all the information you need. Forms work best if they include labeled blanks for all pertinent information and allow the user to check or circle rather than having to write words or numbers (See Appendix 3 for some examples of forms).
Include information such as the name(s) of the person(s) collecting the data, the location, and date of monitoring; a qualitative description of the vegetation, such as the names of the plants or types of plants (native vegetation, annual/perennial weeds, trees, etc.) and stage of growth (germinating, flowering, setting seed, etc.); a quantitative description, such as percent cover, plant density, size of the patch, or if possible, the number of plants.
Note special conditions such as unusual weather events and record treatment history, including information on treatment applications (who, when, where, how, cost, difficulties, and successes). This will allow you to evaluate and fine-tune treatments.
Set Treatment Thresholds
Setting treatment thresholds includes prioritizing and balancing treatments with resources. Weeds will be treated when populations increase beyond a predetermined level. This level will largely depend on the characteristics of the site and weed. In some cases the level may be no weeds at all, and in other cases the number of weeds you can tolerate may be much greater.
Considerations for Setting Priorities
What is the size of the weed population? The opportunity for control is related to the infested area. Small patches can be more easily controlled than large infestations.
What is the level of the threat? Is the tansy ragwort population changing? Is it in an area where soils are frequently disturbed? Does it threaten agriculture, pastures, or rangeland? Is it encroaching on critical habitat for a rare, threatened, or endangered species? Is it displacing the best examples of native communities?
What resources are available? Do you have the resources required for carrying out your goal?
With the advent of herbicides, prevention, as a weed management technique, has often been neglected; however, it is a practical, cost-effective, and extremely important part of noxious weed control.
General Weed Prevention Measures
(Adapted from Fay et al. 1995).
Revegetation - Follow-up Weed Prevention
Establishing dense, competitive vegetation can help permanently replace weeds. Revegetation is critical in preventing weed infestations in areas where the soil has been disturbed or the vegetation removed. In some situations you may be able to encourage desirable vegetation that is already in place; but because of the aggressive nature of tansy ragwort, it is more likely that you will need to thickly sow seeds of desirable, competitive plants.
Apply Management Methods
No individual method will control tansy ragwort in a single treatment; diligence and persistence will be required over a number of years to subdue this weed. The treatment methods described in this section will help you to design an integrated program that will suit the circumstances of your particular situation.
Biological control does not aim to eradicate weeds, but to keep them at low, manageable levels. After their introduction, biocontrol agents can take 5 to 10 years to become established and increase to numbers large enough to reduce the density of the target weed. Once established, effective biological controls provide an inexpensive, long-term, and non-toxic means to control weed populations. Since insects have specific requirements for growing and thriving, it is important to match the insect to the weed management site. Understanding these requirements will help you integrate the insects into other weed control efforts. When you release biocontrols, continue using other control methods on the perimeter of the release site, but avoid using them where they might adversely impact the insect population.
Biological control is very successful wherever it has been attempted in Oregon and Northern California. Studies have shown that following introductions of the biocontrol agents, ragwort density declines to low levels, and it is replaced by more desirable vegetation composed mostly of perennial grasses. Studies analyzing the economic benefits of biological control programs in the states have estimated significant savings. In Oregon, for example, the net benefit of the biological program is estimated to be over $5 million annually, mostly due to the avoidance of cattle poisonings (Coombs et al. 1996).
The information provided below is only a summary. For more information consult Biological Control of Weeds in the West (see Bibliography) or contact commercial weed biocontrol insectaries (see Insectaries).
The seed fly has a broad distribution in the Pacific Northwest and has even been found in areas where the cinnabar moth and flea beetle have not been able to establish. The seed fly is not very effective on its own, but may help weaken ragwort as part of a combination of biocontrols (Coombs et al. 1998; McEvoy et al. 1991).
Early summer sheep grazing may be used effectively to reduce ragwort populations in pastures. During the summer period, tansy ragwort is considered a good feed for sheep, and because the lethal dose of tansy ragwort for sheep is about 200 to 300% of body weight, acute poisoning is rare. Few studies have looked intensively at the effects of different grazing regimes or stocking rates, but grazing would probably be more effective on the rosette stage. Grazing later in the year might stimulate the plants to develop multiple crowns. Avoid heavy grazing during early fall rains, which tends to promote ragwort seedling establishment (Popay and Field 1996; Sharrow and Mosher 1982; Amor et al. 1983; Cheeke 1985; Coombs et al. 1991; Wardle 1987).
Recent research offers the potential of controlling tansy ragwort in bull beef systems and on dairy farms. Betteridge et al. (1994) demonstrated that a low stocking rate of sheep in a predominantly cattle grazing system can give effective control of ragwort. Ewe hoggets (one year-old sheep), set-stocked or mob-stocked at 4 or 7.5 stock units/acre were used to control tansy ragwort in a bull beef grazing trial. Set- stocking caused higher tansy ragwort mortality than mob-stocking and 7.5 stock units/acre resulted in greater mortality than 4 stock units/acre.
Hand pulling is only effective where there are a few plants in their first year of growth. In areas where ragwort has been established, periodic re-treatment will be necessary, as pulling can cause disturbances and allow seed germination. Pull plants when soils are moist to facilitate the complete removal the root mass (Read 1998).
Mechanical control of established stands of tansy ragwort is only effective when the root system can be either entirely removed or frequently cultivated, which prevents the growth of seedling and root sprouts.
Flame throwers or weed burners can be used as spot treatments to heat-girdle small patches of tansy ragwort seedlings. A flame thrower has a nozzle similar to a welding torch and is fueled by a portable propane tank. This technique can be used in sensitive areas or at sites with inefficient fuel loads. In one study, flaming successfully killed 93% of ragwort seedlings, and the seeds on mature plants were not viable (Poole and Cairns 1940).
Deep mulching (12 inches or more) with straw was used as a control method prior to the widespread availability of herbicides. Unless dense, competitive vegetation or hostile habitat surrounds the patch, mulch should extend 15 ft or more beyond the perimeter of the patch to prevent roots or recently dispersed seeds from sprouting. The mulch layer should be maintained for at least three years to kill the root systems of the plants.
In IVM programs, herbicides are considered transition tools that enable the manager to suppress weeds and replace them with desirable, competitive vegetation. Thus, it is important to select the least-toxic, low-residual herbicide that is effective against the target weed, and to apply them in a judicious manner.
The following links discuss the primary considerations when using herbicides: Use Herbicides Properly, Herbicide Information Resources, Criteria for Selecting an Herbicide, and Application Methods.
In general, herbicides should be applied during the seedling or early rosette stages. When mature tansy ragwort patches are small and isolated, it is possible to eradicate them by localized spot treatment. Makepeace and Thompson (1982) obtained good results using a rope wick applicator.
Applying herbicide to plants when tansy ragwort is most susceptible (preferably before seeds are produced) is crucial to the effectiveness of the treatment.
Amor, R.L, D.W. Lane and K.W. Jackson. 1983. Observations on the influence of grazing by sheep or cattle on the density and cover of ragwort. Australian Weeds. 2(3): 94-95.
Bain, J.F. 1991. The biology of Canadian weeds. 96. Senecio jacobaea L. Canadian Journal of Plant Science 71: 127-140.
Bedell, T. E., R. E. Whitesides, and R. B. Hawkes. 1981. Pasture management for control of Tansy ragwort.Pacific Northwest Cooperative Extension Publication no. 210, 6 pp.
Betteridge, K, D.A. Costall, S.M. Hutching, B.P. Devantier, and Y. Liu. 1994. Ragwort (Senecio jacobaea) control by sheep in a hill country bull beef system. Proc. New Zealand Plant Prot. Conf. 47: 53-57.
Black, W.N. 1976. Effects of herbicide rates and time of application on the control of tansy ragwort in pastures. Canadian Journal of Plant Sci.ence 56: 605-610.
Cameron, E.1935. A study of the natural control of ragwort (Senecio jacobaea L.). Journal of Ecology 23: 265-322.
Cheeke, P.R. 1985. Dietary additives for protection against pyrrolizidine alkaloid toxicosis in livestock, pp. 89-97. In: A.A. Seawright et al., Plant Toxicology. Proceedings of the Australia-U.S.A. Poisonous Plants Symp., Brisbane. Queensland Poisonous Plants Commission, Animal Research Institute, Yeerongpilly.
Coles, P.G. 1967. Ragwort control with picloram. Proceedings of the 20th New Zealand Weed and Pest Control Conference 32-36,
Coombs, E.M., T.E. Bedell, and P.B. McEvoy. 1991. Tansy ragwort (Senecio jacobaea): Importance, distribution, and control in Oregon. In: James et al., Noxious Range Weeds, Westview Press, Boulder, CO.
Coombs, E., H. Radtke, D.L. Isaacson, and S.P. Snyder. 1996. Economic and regional benefits from the biological control of tansy ragwort Senecio jacobaea in Oregon, U.S.A. Proc. IXth International Symposium on Biological Control of Weeds 21-26 January, Rondebosch, South Africa.
Coombs, E., C. Mallory-Smith, L.C. Burrill, R.H. Callihan, R. Parker, and H. Radtke.1997. Tansy Ragwort Senecio jacobaea L. Pacific Northwest Extension Publication 175. OR, ID, WA. Oregon State Universtiy Extension Service.
Coombs, E., P.B. McEvoy, and C.E. Turner. 1998. Tansy ragwort. In: R.L. Sheley and J.K. Petroff (Eds). The biology and management of noxious rangeland weeds. Submitted, Oregon State University Agricultural Publications, Corvallis.
Deinzer, M.L., P.A. Thomson, D.M. Burgett, and D.L. Isaacson. 1977. Pyrrolizidine alkaloids: their occurrence in honey of tansy ragwort (Senecio jacobaea). Science 195: 497-499.
Dempster, J.P. 1982. The population ecology of the cinnabar moth, Tyria jacobaeae L. (Lepidoptera, Arctiidae). Oecologia 7: 26-67.
Dewey, S.A. and J.M. Torell. 1991 What is a noxious weed? In: James et al., Noxious Range Weeds. Westview Press, Boulder, CO.
Forbes, J.C. 1985. The impact and control of ragwort (Senecio jacobaea and Senecio laquaaticus) in grassland. British Grassland Society Occasional Symp. no. 18. Weeds, pests, diseases of grass-land and herbage legumes. Crop Prot. Mon. no. 29 pp. 147-154.
Frick, K.E. 1970. Ragwort flea beetle established for biological control of tansy ragwort in Northern California. California Agriculture 24(4):12-13.
Fuller, T.C., and G.D. Barbe. 1985. The Bradley method of eliminating exotic plants from natural reserves. Fremontia 13(2):24-25.
Giles, C.J. 1983. Outbreak of ragwort Senecio jacobaea poisoning in horses. Equine Veterinary Journal 15: 248-250.
Gilkey, H.M. 1957. Weeds of the Pacific Northwest. Oregon State College, Corvallis, 382-383.
Goeger, D.E., P.R. Cheeke, J.A. Shmitz, and D.R. Buhler. 1981. Toxicity of tansy ragwort Senecio jacobaea to goats. American Journal of Veterinary Research 43: 252-254.
Harris, P., A.T.S. Wilkinson, M.E. Neary, and L.S. Thompson. 1971. Senecio jacobaea L., tansy ragwort [Compositae], pp. 97-104. In: Kelleher and Hulme, Biological Control Programmes Against Insects and Weeds in Canada. 1969-1980. Commonwealth Agricultural Bureaux, Franham Royal, Slough, 410 pp.
Hawkes, R.B. and Johnson, G.R. 1978, Longitarsus jacobaeae aids moth in the biological control of tansy ragwort, pp. 193-196. In: Proceedings of the IVth International Symposium on Biological Control of Weeds. T.E. Freeman, Univ. Florida, Gainseville.
Irvine, H.M., Forbes, J.C. and Draper, S.R. 1977. Effects of 2,4-D on the water-soluable carbohydrate content of ragwort (Senecio jacobaea L.) leaves. Weed Research 117: 169-172.
Jacobs, J.S., R.L. Sheley, and B.D. Maxwell. 1997. Yellow starthistle population dynamics model. Colorado Weed Management Association 1997 Annual Conference Proceedings. PO Box 1910, 461 E. Agate Ave. Granby, CO 80446-1910
James, L.F., M.H. Ralphs, and D.B. Nielsen. 1988. The Ecology and Economic Impact of Poisonous Plants on Livestock Production. Westview Press, Boulder, CO.
James, R.R., P.B. McEvoy, and C.S. Cox, eds. 1992. Combining the cinnabar moth (Tyria jacobaeae) and the ragwort flea beetle (Longitarsus jacobaeae) for control of ragwort (Senecio jacobae): an experimental analysis. Journal of Applied Ecology: 29: 589-596.
Lacey, CA., et al. 1988. Bounty programs—an effective weed management tool. Weed Technology. 2:196-197
Makepeace, W. and A. Thompson. 1982. Ragwort control using a rope wick applicator, pp. 256-260. Proceedings of the 35th New Zealand Weed and Pest Control Conference .
Maxwell, B. " YST software." Personal e-mail (9 Feb 1998)
McEachen, H. Pers. comm. 1998. Agronomist. PO Box 96. Mesa, WA 99343.
McEvoy, P.B. 1983. Dormancy and dispersal in dimorphic achenes of tan-sy ragwort, Senecio jacobaea L. (Compositae). Oecologia 61:160-168.
McEvoy, P.B. 1984. Seedling dispersion and the persistence of ragwort Senecio jacobaea (Compositae) in a grassland dominated by perennial species. OIKOS 42: 138-143.
McEvoy, P.B., C.S. Cox, R.R. James, and N.T. Rudd. 1990. Ecological mechanisms underlying successful biological weed control: field experiments with ragwort Senecio jacobaea., pp. 53-64. In: E.S. Delfosse. Proc. of the VIIth International Symp. on Biological Control of Weeds. Inst. Patol. Veg., Rome/CSIRO, Melbourne.
McEvoy, P.B., C. Cox, and E. Coombs. 1991. Successful biological control of ragwort, Senecio jacobaea, by introduced insects in Oregon. Ecological Applications 1: 430-442.
Miller, D. 1936. Biological control of noxious weeds. New Zealand Journal of Science and Technology 18: 581-584.
Mitich, L.W. 1995. Tansy ragwort. Weed Technology 9: 402-404.
Paul, N.D., P.G. Ayers and S.G. Hallett. 1993. Mycoherbicides and other biocontrol agents for Senecio spp. Pesticide Sci. 37: 323-329.
Pearson, W. 1998. Pers. Comm. County Weed Extension Agent. Stillwater County, Columbus, Montana.
Pemberton, R.W., and C.E. Turner. 1990. Biological control of Senecio jacobaea in Northern California, an enduring success. Entomophaga 35(1): 71-77.
Peterson, J.E., and C.C.J. Culvenor. 1983. Hepatotoxic pyrrolizidine alkaloids, pp. 637-671. In: R.F. Keeler and A.T. Tu, Handbook of natural toxins, V. 1. Plant and fungal toxins. Marcel Dekker, Inc., NY.
Poole, A. and D. Cairns. 1940. Botanical aspects of ragwort (Senecio jacobaea L.) control. Bulletin of the New Zealand Department of Science and Industrial Research 82: 1-66.
Popay, I. and R. Field. 1996. Grazing animals as weed control agents. Weed Technology 10(217-231).
Radtke, H. 1993. An Economic Evaluation of Biological Control of Tansy Ragwort. Executive Summary. Oregon Department of Agriculture State Weed Board, Oregon Depart of Agriculture TDD # (503) 373-7776.
Randall, J.M. and J. Marinelli eds. 1996. Invasive Plants: Weeds of the Global Garden. Brooklyn Bot. Garden , Inc. Brooklyn, NY. 108pp.
Read, R. 1998. Pers. Comm. Regional Vegetation Biologist, BC Hydro. 400 Madsen Rd., Nanaimo, B.C. V9R 5M3.
Rees, N.E., P.C. Quimby, Jr., G.L. Piper, E.M. Coombs, C.E. Turner, N.R. Spencer, and L.V. Knutson, eds. 1996. Biological Control of Weeds in the West. Western Society of Weed Science, USDA/ARS, Montana Dept. Agric., Montana State University, Bozeman, MT.
Schmidl, L. 1972. Biology and control of ragwort, Senecio jacobaea L., in Victoria, Australia. Weed Research 12: 37-45.
Sharrow, S.H., and W.D. Mosher. 1982. Sheep as biological control agent for tansy ragwort. J. of Range Management 35:480-482.
Thompson, A. 1977. Herbicides for spot treatment of ragwort in pasture. Proceedings of the 30th New Zealand Weed and Pest Control Conference pp. 34-37.
Thompson, A. 1983. Pasture weed control by rope wick applicator. Proc. of the 37th N. Zealand Weed and Pest Control Conf. pp. 96-98.
Thompson, A. and Saunders, A.E. 1984. A comparison of 2,4-D and MCPA alone and in combination of the control of ragwort.Proc. of the 37th New Zealand Weed and Pest Control Conf. pp. 33-36.
Thompson, A. and W. Makepeace. 1983. Longevity of buried ragwort (Senecio jacobaea L.) seed. N. Zealand J. of Exp. Ag. 11: 89-90.
University of Northern Iowa. 1993. Integrated Roadside Vegetation Management Technical Manual. Produced by the Roadside Management Prog. To obtain, call Kirk Henderson at 319-273-2813.
Wardle, D.A. 1987. The ecology of ragwort (Senecio jacobaea L.) — a review. New Zealand Journal of Ecololgy 10: 67-76.