This weed, also called Madagascar fireweed and variable groundsel, has become a threat to pasture areas on Hawaii and Maui since its appearance in the state in the early 1980s. Its management is discussed

DuPonte, M.

Fukumoto, G.

Kawabata, A.

Motooka, P.

Nagai, G.

Onuma, K.

Powley, J.

ScholarSpace at University of Hawai'i at Manoa

Madagascar ragwort, also called Madagascar fire-weed and variable groundsel,(1) Senecio madagas-cariensis Poiret, a native of Madagascar and SouthAfrica,(2) has become a serious weed of pastures on theislands of Hawai‘i and Maui.In the early 1980s, Lee Beerman, then with ParkerRanch, reported a “yellow-flowered weed” in pastures nearHäwï, Kohala. From there, within a decade, it had infestedpastures all the way up to Kahuä Ranch. Today it infestspastures and roadsides throughout Waimea and intoHonoka‘a, up the Saddle Road, and is establishing in Kona.Madagascar ragwort has jumped across the island intoKa‘ü, apparently with cattle shipments. On Maui, it infestsroadsides and pastures from ‘Ulupalakua to Kula,Makawao, Pukalani, Ha‘ikü, and Waihe‘e. On Kaua‘i, aninfestation was found on a hydro-mulched road-cut atHalfway Bridge. Because the infestation was confined tothe hydro-mulched area, it was surmised that the ground-cover seed from Australia was contaminated with theweed. Diligent rogueing by the Hawai‘i Department ofAgriculture (HDOA) and the Kauai Invasive SpeciesCommittee seemed to be eradicating the Kaua‘i infestation,but then a new infestation was found in Kalihi Wai.Australian scientists have reported that Madagascarragwort is a serious problem in pastures of QueenslandControl of Madagascar Ragwort(aka Madagascar fireweed, Senecio madagascariensis)P. Motooka1, G. Nagai2, K. Onuma2, M. DuPonte3, A. Kawabata3, G. Fukumoto3, and J. Powley41CTAHR Department of Natural Resources and Environmental Management,2Hawai‘i Department of Agriculture, and 3,4CTAHR Cooperative Extension Service–3Hawai‘i, 4Kahuluiand New South Wales because it depresses forage yieldand is poisonous to livestock, causing yearly losses ofA$2 million.(2)DescriptionMadagascar ragwort is a low, upright, branched herb 4–20 inches high. Its narrow, green leaves are up to 21⁄2inches long and have margins that are either entire(smooth), serrated, or lobed. It flowers profusely withsmall, daisy-like flowers ranging in size from about 3⁄8Published by the College of Tropical Agriculture and Human Resources (CTAHR) and issued in furtherance of Cooperative Extension work, Acts of May 8 and June30, 1914, in cooperation with the U.S. Department of Agriculture. Andrew G. Hashimoto, Director/Dean, Cooperative Extension Service/CTAHR, Universityof Hawaii at Manoa, Honolulu, Hawaii 96822. An Equal Opportunity / Affirmative Action Institution providing programs and services to the people of Hawaii withoutregard to race, sex, age, religion, color, national origin, ancestry, disability, marital status, arrest and court record, sexual orientation, or veteran status.CTAHR publications can be found on the Web site <http://www.ctahr.hawaii.edu> or ordered by calling 808-956-7046 or sending e-mail to ctahrpub@hawaii.edu.Madagascar ragwort flower’s petals andcentral disk are bright yellow; eachflower invariably has 13 petals (photo: R.Heu).Madagascar ragwort produces flowers profusely. The small, daisy-like flowers range in size from about 3⁄8 to 1 inch in diameter.An extensive infestation of Madagascar ragwort in the Saddle Roadarea of the island of Hawai‘i.ALIENPESTALERT!Control of Madagascar RagwortALIENPESTALERT!to 1 inch in diameter. Both the petals and the centraldisk of the flower are bright yellow, and each flowerinvariably has 13 petals. The flowers mature into whitethistle-balls up to 5⁄8 inch in diameter.     Madagascar ragwort is prolific. Each flower producesabout 150 thistled seeds, and each plant produces anaverage of 30,000 seeds. The seeds (a seed type knownas an achene) are dry, cylindrical, and slender. They areabout 1⁄10 inch long and are dispersed by wind or byhitchhiking on passing animals and vehicles. The seedis long-lived, making ragwort a permanent problem ininfested pastures.(1) This weed readily invades pasturesdamaged by overgrazing, drought, or (in Hawai‘i) theyellow sugarcane aphid (Sipha flava). It seems equallyat home in low-elevation, arid pastures as in high-elevation, moist pastures.Methods to control ragwortBiological control. Australian scientists have collectedseveral insects that feed on Madagascar ragwort. How-ever, because the plant is closely related to Senecio lautusForster f. ex Willd., a native Australian plant that is not aweed, the scientists are pessimistic about chances thatrelease of these insects for ragwort control in Australiawill be approved.(3)Biocontrol researchers at HDOA have brought sev-eral natural enemies of ragwort from Madagascar andSouth Africa into their quarantine facility to determinethe suitability of these potential biocontrol agents forrelease in Hawai‘i. Of a total of 11 insects and a fungusthat were collected in late 1999 by the HDOA explor-atory entomologist, only two species still remain as can-didates for biocontrol of ragwort. Host specificity stud-ies have been completed on an arctiid moth whose lar-vae feed voraciously on ragwort foliage. Currently, datais being assembled to justify the release of this speciesfrom quarantine. Studies continue on a tephritid fly whoselarvae feed within and destroy ragwort flowers.(4)Cultural control. Australian agronomists(1) recom-mend pasture management practices that encourage for-age growth and vigor, such as controlled grazing andapplications of fertilizers. Early action is emphasizedbecause of the fecundity and rapid dispersal of Mada-gascar ragwort. Carefully timed mowing may help, butit also may make the problem worse if done at an inop-portune time, such as during drought. Sheep and goatsare less susceptible than cattle to ragwort poisoning andcan be used to graze down the weed. However, whenusing sheep or goats as a control measure it is not advis-able to graze young animals or lactating females inheavily infested pastures during the preflowering stageof the plant, as these animals may be more susceptibleto poisoning than mature or dry females.(5)Chemical control. Madagascar ragwort is sensitiveto several herbicides, including clopyralid, 2,4-D,MCPA, dicamba DGA, glyphosate, and tebuthiuron.Because glyphosate is nonselective, it can only be ap-plied where non-target kill can be tolerated. Or, it canbe applied directly to ragwort with a wipe-on applicatorso that it does not kill other plants in the pasture. Theother herbicides are selective against broadleaf plantsand will not injure grasses at label rates. Of these, MCPAand 2,4-D, a restricted-use herbicide, are the most eco-nomical because they are old products. MCPA, chemi-cally related to 2,4-D, does not require certification touse and is thus the most convenient product for effec-tive control. MCPA application to rank growth of rag-wort requires 2 lb/acre or 2 qt/acre ($11/acre). Younginfestations require half that. Where forage legumes aremixed with grasses, the amine salt formulation of 2,4-Dwould be preferable because of its mild effect on le-gumes such as white clover (MCPA and 2,4-D estersare more injurious than 2,4-D amine on legumes). Inany case, best results are obtained when ragwort is youngand succulent and not drought stressed.In general, a single herbicide application will notsuppress Madagascar ragwort permanently. Culturalpractices must be changed to prevent reinfestation (seeCultural control, above).Report sightingsSightings of this weed should be reported to the nearestoffice of the Hawaii Department of Agriculture.References cited(1). Watson, R., T. Launders, and J. Macadam. 1984. Fireweed. Agfact P7.6.26. NewSouth Wales Dept. of Agriculture, Scone, Australia.(2). Holtkamp, R.H., and J.R. Hosking. 1993. Insects and diseases of fireweed, Seneciomadagascariensis, and the closely related Senecio lautus complex. Proc., 10th Australianand 14th Asian-Pacific Weed Science Soc. Conf., Brisbane, Australia. p. 104–106.(3). Personal communication, Dr. G. White, entomologist, Queensland Dept. of Lands.(4). Personal communication, Ken Teramoto, HDOA Biocontrol Section.(5). Personal communication, Dr. Mark Thorne, UH-CTAHR.CTAHR publication WC-2 (revised)—Oct. 2004.  Printed with support from the Hawai‘i Department of Agriculture.Numbers to call:O‘ahu 973-9538Kaua‘i (also Ni‘ihau) 274-3069Maui  (also Moloka‘i, Läna‘i, Kaho‘olawe) 873-3555Hawai‘i 974-4140

Control of Madagascar Ragwort (aka Madagascar Fireweed, Senecio madagascariensis)

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Control of Madagascar Ragwort (aka Madagascar Fireweed, Senecio madagascariensis)

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