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The right combination of plant species, fertility,and grazing is essential in good pasture management.Weed control also is important. Because of the toxicproperties of the weed tansy ragwort, pasture man-agement for its control is of extreme importance. Thetoxins in this weed can kill domestic livestock, althoughsheep are tolerant to large dosages.

Tansy ragwort is estimated to occur on 3¼ millionacres in western Oregon, where 2 out of every 5 acresof pasture are infested. More than 112,000 acres ofpasture in western Washington contain ragwort. Tansyragwort has been reported in Idaho and is considereda serious potential weed problem that has not yetreached a level of economic importance. Most ragwortis on forested and clearcut lands. The plant spreadsby seed, and grows and reproduces rapidly whenpastures are not well managed. Livestock producers,part-time producers, and horse owners need to learn tocontrol tansy ragwort to stay in production.

Plant growthTansy ragwort (Senecio jacobaea) was first re-

ported in Oregon in 1922 after introduction into theUnited States from Europe. It is found in drier regionsof Europe, Asia, and Siberia, where it can survivetemperatures of 20°F or lower. Tansy ragwort hasspread across western Oregon and Washington. Plantscan withstand large variations in soil moisture condi-tions and will tolerate the hot, dry summers of eastern

Tansy ragwort leaves and the blade region near the tip aredeeply lobed. Leaf color varies from light to dark green.

Oregon and Washington, where it has been found innumerous locations. It is believed to be capable ofestablishing itself throughout the Pacific Northwest.Tansy ragwort can become established rapidly in forestclearcuts and can develop in irrigated, nonirrigated,and woodland pastures. It occasionally occurs in an-nually tilled cropland. The heaviest infestations nowoccur in the coast range.

Tansy ragwort has conspicuous, daisy-like goldenflowers, which appear over an extended period. Therosette has irregular, lobed leaves, 5 to 9 inches long,

In the pasture complex, livestock often cannot separate therosette stage of tansy ragwort from desirable forage.

PNW 210 Reprinted August 1984A Pacific Northwest Cooperative Extension Publication

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attached directly to the main stalk. Plant color isvariable, ranging from light to dark green.

Tansy ragwort is a biennial, but can develop as ashort-lived perennial. Seeds can germinate in the fallor spring. The vegetative stage is a low, dense, rosette.Plants that emerge early in the fall and develop arosette before winter usually bloom during the followingsummer, produce seeds, and die. Plants that emergelate in the fall or in the spring are more likely to remainvegetative during the summer and bloom during thesecond summer. If the plant is cut or broken beforeit blossoms, it may regrow and flower during the thirdyear.

Seed is the primary method of ragwort dispersal.It is spread by wind, water, and animals, includinghumans. Transportation of contaminated hay and strawfrom western Oregon and Washington by hunters is amajor cause of movement east of the Cascade Moun-tains. A single plant may produce 150 thousand seeds,which can remain viable in the soil for 3 years orlonger. Most seeds do not move more than a few feetfrom the parent plant.

Toxic propertiesLivestock normally will not graze tansy ragwort if

more desirable forage is available. Small plants, grow-ing in intimate association with grasses and cloversor plants that may occur in hay, cannot be excludedselectively. Second-year plants are not grazed byhorses and cattle until all other preferred forage hasbeen removed.

Tansy ragwort contains at least six pyrrolizidinealkaloids. Concentration of alkaloids greatest inflowers, then leaves, roots, and stems, and averagesabout 0.18 percent of the dry weight. The alkaloidsthemselves are not toxic. In the presence of certainliver enzymes, however, pyrrolizidine alkaloids areconverted to pyrroles. When enough conversion topyrrole has occurred, the liver ceases to functionnormally and the animal dies. The liver damage iscumulative with time and dose.

Cattle and horses are affected seriously; goats maysuffer poisoning; sheep are generally not poisonedby tansy ragwort. Experiments show that dry tansyragwort (weighing 2 percent of a weaned calf's bodyweight) fed over a 15- to 30-day period is enough tokill the animal. The toxic effect persists even whenanimals are removed from tansy ragwort after ex-posure. In the experiments this amounted to only 7 per-cent of the daily food intake. Ragwort fed to goats at1 percent of their body weight for 25 days, during lacta-tion (for a total of 125 percent of the goat's bodyweight), caused abortions and subsequent death ofthe does. It is unlikely an animal could graze thatmuch on its own, since it represents about one-thirdof normal daily needs. Pyrrolizidine alkaloids have beenfound in milk from cows and goats fed a diet containingtansy ragwort. Susceptibility to tansy ragwort poisoningvaries greatly among individual animals. Livestock inpoor body condition are most rapidly affected becauseof pre-existing liver conditions.

Sheep are not easily poisoned by tansy ragwort.Ragwort is not rejected by sheep as it is by cattle andhorses. Sheep may graze green ragwort plants prefer-entially in summer when other plants are dry. Theleaves of tansy ragwort contain in excess of 10 percent

crude protein and flowers contain 14.5 percent. Inexperiments, sheep have eaten more than twice theirbody weight in tansy ragwort and demonstrated noevidence of toxicity. Cattle are poisoned after ingesting2 to 8 percent of their body weight. Younger animalsare most sensitive. Sheep apparently do not convertpyrrolizidine alkaloids to pyrroles in their livers. It isnot known whether sheep reconvert pyrrolizidine al-kaloids into new molecules in the rumen or whetherthey don't have the liver enzymes to convert theminto the toxic form. The OSU School of VeterinaryMedicine offers blood enzyme tests for cattle, horses,and sheep. The tests can determine relative levels oftoxin accumulation.

Costs of no controlEverything has a price tag. Inadequate pasture

management is no exception. Losses from reducedperformance of unthrifty animals and dead animalsare real, as is competition by tansy ragwort for space,moisture, and nutrients. Dense populations of ragwortmay reduce forage yields by 50 percent or more. The"cost" of anxiety when family horses are involvedcannot be measured.

Cultural management

In a poorly managed, ragwort-infested pasture, the potentialfor damage to cattle is high.

Cattle will graze tansy ragwort in poorly managed pastureswhere other forage is limited.

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The incidence of tansy ragwort is lower on well-managed pastures. The following practices are sug-gested to keep plants from setting viable seeds andto help achieve and maintain high forage productivity.

Plant improved, high-yielding pasture species.Pastures with subclover or white clover and perennialgrasses produce three to five times more forage, ofhigher quality, than native or annual grass pastures.Vigorous plants also provide more competition to tansyragwort.

Fertilize according to soil needs. Clovers requirephosphorus and sulfur primarily; grass needs nitrogen.Clover can provide nitrogen through nitrogen fixation,but phosphorus, sulfur, and several other nutrientsmust be provided through chemical fertilizers ormanure. Test soil to determine phosphorus needs. Con-sult OSU Fertilizer Guides 1, 2, and 63 or WSU FertilizerGuides 1, 16, and 20. Instructions and sampling con-tainers are available at county Extension offices.

Maintain a dense stand. Tansy ragwort seed cangerminate and establish in "holes" or "broken" spotsin the stand more easily than in dense growth. Estab-lish a good stand in the beginning. For example, tansyragwort is seldom found in tall fescue growing in high-way rights-of-way.

Graze uniformly. Good grazing programs stimu-late good plants to be more competitive and promotea higher proportion of clover. Subdivide pastures withfences and move stock from unit to unit in a plannedsequence to avoid overgrazing.

Avoid winter grazing by cattle and horses andgrazing during irrigation. Large animals open "holes"in a good grass-clover pasture when soils are wet.Some winter use of excess grass growth by sheep orlight cattle allows more light to reach the lower-growingclover and stimulates tillering of grass.

Maintain a balance between grass and cloverspecies. A proper forage mixture extends seasonalproduction, increases total productivity, and extendsduration of competition to invading ragwort plants.

If tansy ragwort is already a problem in pasture,consider the reasons it became a problem. It is pos-sible that some management practices promotedestablishment. If preferential grazing is initiated tooearly in the life of the pasture stand, the soil dis-turbance may cause ragwort to develop from seed.Grazing either after new plants were firmly establishedor when everything was green should have minimizedthe invasion.

Continuous sheep grazing will remove tansy ragwortand keep it out. Observations suggest that the controloccurs by keeping the plants from going to seed.Constant grazing may keep a plant vegetative andallow a second-year plant to develop into the thirdyear. If not grazed, third-year plants will flower beforethey die. If sheep are removed and a seed source ispresent, tansy ragwort will reinfest the area. Mixedgrazing by cattle and sheep results in more uniformforage utilization. Sheep can be used as a "precondi-tioning" agent ahead of cattle. Graze sheep from Mayto early June at an intensity that forces them to con-sume all tansy ragwort plants. This prevents ragwortplants from setting seed. Intense grazing for 2 to 3years in sequence will reduce tansy ragwort populationsso that cattle could be grazed safely during the grow-

ing season. Remove cattle if young tansy ragwort isbeing eaten.

Mowing is not effective in reducing tansy ragwortpopulations. Theoretically, mowing should keep plantsfrom blooming if clipping is properly timed. In prac-tice, this is virtually impossible to achieve.

Hand pulling and digging can be an effective toolin keeping second-year plants from setting seed. Ifplants start to bloom some viable seed can be pro-duced. Hand labor requires persistence and intensiveeffort and is most applicable to spot infestations orsmall acreages. Unless the entire root system is re-moved, however, regrowth frequently occurs fromsegments left in the soil.

Chemical control

Tansy ragwort was controlled in test plots using 2,4-D ap-plied at the rosette stage.

Effective and economical control of tansy ragworthas been accomplished with 2,4-D. Application is madeduring the early spring (April) or midfall, after rainshave initiated new growth. Use amine, low-volatileester (LVE), or emulsifiable acid forms of 2,4-D whenragwort is small or in the rosette stage. Apply 2pounds acid equivalent per acre. If the 2,4-D formula-tion is 4 pounds-per-gallon use 2 quarts per acrein 20 gallons or more water. When applications arecorrectly timed, 2,4-D amine without wetting agent at2 pounds per acre has given good to excellent ragwortcontrol with minimum clover injury. Fall applicationscause less clover injury than spring treatments.

If tansy ragwort is more mature and has a largerosette or the flowering stalk has elongated, usedicamba (Banvel) or dicamba + 2,4-D. Apply 1 poundactive (1 quart) of dicamba or 0.5 to 1 pound dicambapIus 2 pounds (2 quarts) of 2,4-D per acre. Apply in20 or more gallons of water.

After plants have bolted and developed a seed-stalk, control with 2,4-D is less effective. The additionof dicamba results in increased control of matureplants and is effective in stopping the development ofseeds in the flower. For best results from spot treat-ment, wet plants until spray begins to drip. Make ap-plication on a warm sunny day. Spray when no rain isexpected for a minimum of 6 hours. After treatment,plants die slowly.

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Always follow label iiistructions of the productbeing used. Read the label carefully for grazing re-

strictions before applying any herbicide. Note: Ap-plication of 2,4-D may injure clovers. Dicamba willkill clovers.

Biological control

Larvae of the cinnabar moth can reduce tansy ragwort popu-lations to low levels in areas where other controls are notpractical or economical.

The adult cinnabar moth is normally seen from April to July.

Insects are considered primary bio-control agents,but proper use of sheep grazing is also a form ofbiological control. Plant diseases may play an im-portant role in the future, but presently there are nospecific diseases used to control tansy ragwort.

Th.e cinnabar moth, Tyria jacobaeae, was intro-duced into the Pacific Northwest in 1960 and is nowwidespread throughout the ragwort-infested areas westof the Cascade mountains. Cinnabar larvae feed on thefoliage and flowers of ragwort, and in large numberscan totally defoliate the plant. Although the insect iswidespread, not all areas have colonies. The followingwill aid in collection and successful establishment ofcinnabar larvae from established colonies to new sites.The larvae should be nearing maturity, at which timethey will be about 1 inch in length. Mature larvae areusually available from late June through July. An easymethod to collect larvae from ragwort is by simply tap-ping the flowerheads into a large grocery bag, since thelarvae readily fall when disturbed. Some ragwort foliageand stems should be placed in the bag as a source offood while in transit, and the bag should be kept shadedand cool until the larvae are released.

The new release site should have ample ragwort tosupport the larvae; however extensive stands are notnecessary. Dump the larvae on flower clusters at thenew site, but do not disperse them too widely. Do notbe concerned if they fall to the ground. They will relo-cate tansy ragwort plants rapidly. In a dense stand ofragwort, 1,000 larvae could be released on an areaof 200 square feet. The site should be well drainedand should not be subject to winter flooding, sincethe insect overwinters as a pupa (cocoon) in litteron the soil and will drown on wet or soggy sites. The

The adult flea beetle is a new addition in biological controlof tansy ragwort.

site should not be heavily grazed, as livestock tramplingcan destroy overwintering pupae. The cinnabar mothcan be used where grazing occurs, but a protectedsite within the grazed area, such as a fence row orbrush patch, should be chosen to protect the initiallarval release. If larvae are not available for collection,consult your Extension agent or county weed controlsupervisor, as most counties are actively involved inthe cinnabar moth program.

Even the severe defoliation by cinnabar larvae oftendoes not kill ragwort. During late August and Septem-ber, after the cinnabar larvae have formed pupae, rag-

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wort will produce some regrowth and secondary flower-ing. Although cinnabar defoliation does eliminate muchseed production, as well as ragwort foliage, some viableseed is produced by late season flowering.

Since the cinnabar moth offers only partial controlof ragwort, a second insect, known as the ragwortflea beetle, Longitarsus jacobaeae, is being releasedin the Pacific Northwest. The adult beetles feed on thefoliage during the fall and the larvae feed in the leafpetioles, crowns, and roots during the winter andspring. This feeding by the beetle larvae augments thecinnabar larval damage, coming at a time when thecinnabar moth is inactive. Thus, pressure is applied tothe plant throughout the year and much better controlcan be expected where a combination of the two in-sects is used.

While many people have been involved in distribu-tion of the cinnabar moth, the flea beetle is small andmore difficult to collect. Specialized vacuum insectcollecting equipment is needed, and the cost of thisequipment may prohibit the public from getting in-volved in collecting flea beetles. The Oregon Depart-ment of Agriculture conducts a flea beetle collectionand distribution program each autumn, beginningabout the first of October. At that time beetles aremade available through county Extension agents andcounty weed control supervisors. Sites with active cin-nabar moth colonies are given preference for fleabeetle releases, since a combination of the two insectsgives the best control.

Biological control of tansy ragwort is not applicableto all types of grazing land. A combination of thecinnabar moth and the ragwort flea beetle may take4 to 5 years or more to control the plant. On high-value, improved pasture, it is not economically feasibleto wait that long, and chemical control is a morepractical approach.

Native pasture and open rangeland are areas wherebiological control can be used to the best advantage.These lands are often too low in value, or the terraintoo rough or inaccessible, for chemical control to befeasible. Once established, biological control organismsare self-perpetuating and can spread over most typesof terrain. Where rangelands adjoin managed pasture,an active biological control program can help to keepragwort from spreading into the improved pasture.Biological agents can be used along stream coursesand fence rows, and in wood lots and waste areas.Once control of ragwort has been achieved for anarea, biological agents can maintain the plant at lowlevels with little or no further expenditure.

Integrating management practicesIn practice, the pasture manager is looking for a

combination of several controls. Each situation hasdifferent characteristics and requires personal evalua-tion. Typical pasture situations include:

Management with a light infestationOptions in-clude all control practices, but a real attempt shouldbe made to remove the flowering source.

On non-brushy pastures where good visibility exists,ragwort can be killed through spot spraying and by

pulling. In this way no damage will occur to clover.All roots must be removed if plants are pulled.

Similar procedures are useful on brushy pastures,but some plants may be missed. This approach is onlysuccessful when the seed source is entirely removed.With low populations of ragwort, judicious stockingwith cattle and horses should result in no ragwort con-sumption, even in the dry season. Grazing young feederanimals would be preferable to breeding stock, sincefeeders will be slaughtered before they accumulatelethal amounts.

Management with a heavy Infestation (both withinand outside the pasture) Where there have been nosheep grazing or where no grazing of any kind hastaken place, ragwort populations can be high. Thepopulation of second-year plants will be large, andthe potential for seed production is large. Remove allcattle and horses. Introducing sheep could effect areduction of tansy ragwort over a short period, prob-ably 2 years, but reinvasion will occur if seed sourcesare close by. The most rapid cleanup procedure is abroadcast spray application. Some clover damage mayresult. Long-term success is maximized by continuedbiological control using sheep or available insects afterherbicide application.

Insects take time to increase their population, soearly success will be limited. Pulling second-yearplants will be futile, since populations are high. Mow-ing, unless frequent and thorough, will not reducepopulations, since some plants will escape to makeseed.

Where good populations of desirable plants don'texist, complete renovation of the pasture may benecessary. In this case, a year's delay in re-establishinga clover-grass pasture will pay dividends. During theinterim year, an annual crop may be grown or theland kept fallow. In either case, cultivation must betimely during the crop or fallow year to insure thatgerminated ragwort plants are turned under beforeclover-grass is planted.

ConclusionsPurposeful management can result in pastures free

of tansy ragwort. Promoting vigorous grass-clover com-petition through proper fertilization and grazing prac-tices is the first line of defense to minimize futureragwort problems. Reinvasion from nearby areas isever-present, even after a ragwort cleanup programhas succeeded. Continued monitoring will be neces-sary to insure that new plants don't get started. If newplants appear, hand pull, dig, use chemical spot treat-ment, or periodically graze sheep. Even if cinnabarmoths and flea beetles are present, some buildup ofragwort probably will occur before insect populationsincrease and provide control.

Exercising good management of pastures makesbetter neighbors. Keeping plants from blooming andultimately permitting better forage plants to succeedin their places will result in more production, healthylivestock, and a positive managerial reputation in thecommunity.

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ILl A (II IISUflWflI

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Pacific Northwest cooperative Extension bulletins are joint publicationsof the three Pacific Northwest statesOregon, Washington, and Idaho.Similar crops, climate, and topography create a natural geographic unitthat crosses state lines. Since 1949 the PNW program has publishedover 250 titles. Joint writing, editing, and production has preventedduplication of effort, broadened the availability of faculty specialists,and substantially reduced costs for the participating states.

This publication was prepared by Thomas E. Bedell, Extension rangelandresources specialist, Oregon State University; Robert B. Hawkes, ento-mologist, Oregon State Department of Agriculture; and Ralph E. White-sides, former Extension agronomist, weed control, Oregon State Uni-versity. It was reviewed by Extension weed control specialists in Wash-ington and Idaho.

The Oregon State Department of Agriculture, Leonard Kunzman, director,cooperated in manuscript preparation and review and, through a grant,shared substantially in costs of printing and the color illustrations in theoriginal (1981) edition.

Published and distributed in furtherance of the Acts of Congress of May8 and June 30, 1914, by the Oregon State University Extension Service,0. E. Smith, director; Washington State University Cooperative Extension,J. 0. Young, director; the University of Idaho Cooperative ExtensionService, H. R. Guenthner, director; and the U.S. Department of Agricul.ture cooperating.

The three participating Extension Services offer educational programs,activities, and materials without regard to race, color, national origin,sex, or disability as required by Title VI of the Civil Rights Act of 1964,-Title IX of the Education Amendments of 1972, and Section 504 of theRehabilitation Act of 1973. The Oregon State University Extension Service,Washington State University Cooperative Extension, and the Universityof Idaho Cooperative Extension Service are Equal Opportunity Employers.25/0/25

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