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Species Ageratum conyzoides
Author L.
Family Asteraceae
Weed Type Broadleaf
Global Description Terrestrial, annual, erect herb, up to 120 cm tall. Taproot white or brown. Stem rounded, solid, hairy. Stipules absent. Leaves simple, not divided or lobed, opposite, stalked, ovate, hairy or not on both sides, margin coarsely dentate, apex acute, base rounded or truncate, pinnately veined. Flowers bisexual, grouped together in a terminal head, consisting of tubular flowers only, sessile, white or blue, petals 5. Fruit an achene, pappus present. The species has great morphological variation, and appears highly adaptable to different ecological conditions.
General Habit An erect, herbaceous annual plant, 30 to 80 cm tall.
Stem Stems are covered with fine white hairs, stem is often red.
Leaf Leaves are opposite, pubescent with long petioles and include glandular trichomes, leaves covered with fine hair, ovate, to 3 inches long by 2inches wide, more or less pointed apex, margin regularly serrated, with blunt teeth.
Inflorescence Terminal, contains 30 to 50 pink flowers arranged as a corymb and are self-incompatible.
Flower The flowers are hermaphrodite and are pollinated by insects, individual flower heads are ¼ inch across with large numbers of tubular flowers surrounded by 2 or 3 rows of narrow pointed bracts with membranous margins.
Fruit A slender achene encircled with 5 white pointed scales, black in colour.
Seed Seeds are positively photoblastic, and viability is often lost within 12 months, the dark seeds have scales and ends in a needle-like shape.
Biology Reproduction by seeds. Seeds are dispersed by wind and water. Flowering all the year round and may produce up to 40 000 seeds per plant.
Ecology The species is widespread in moist uplands, hydromorphic and temporary, shallow flooded lands. The plant prefers light (sandy), medium (loamy) and heavy (clay) soils, acid, neutral and alkaline soils.
Origin Central and South America (Wagner et al., 1999; p. 255), now a worldwide weed.
World Distribution Tropical and subtropical area, Africa, Indian continent, S.E.Asia, Malesia, Central and South America.
Global Weediness May become troublesome in plantations after grasses have been suppressed. The relative tolerance to flooding, abundant seed production and rapid germination of this species makes it a successful weed in rain-fed rice cropping systems in Africa.
Local weediness Benin: Frequent but not abundant. Burkina Faso: Frequent but not abundant. Chad: Rare and not abundant. Côte d'Ivoire: Frequent and usually abundant. Ghana: Frequent and usually abundant. Kenya: Frequent but not abundant. Mali: Frequent but not abundant. Nigeria: Rare but abundant when present. Senegal: Rare but abundant when present. Tanzania: Frequent and usually abundant. Uganda: Frequent and usually abundant.
Global control Ageratum conyzoides can be readily controlled when young by hand pulling or hoeing. Seedlings and young stages readily controlled by 2,4-D, MCPA and other growth regulators that are used on cereal crops. Management options:
Uses A. conyzoides has been reported to have medicinal and bioherbicidal applications (Xuan et al., 2004). Such uses however are not widespread. The leaves and the flowers yield 0.2% essential oil with a powerful nauseating odour . The oil contains 5% eugenol, which has a pleasant odour. The oil from plants growing in Africa has an agreeable odour, consisting almost entirely of eugenol. In Brazil A. conyzoides is used as an infusion is prepared with the leaves or the entire plant and employed to treat colic, colds and fevers, diarrhea, rheumatism, spasms, and as a tonic. It is also highly recomended there for burns and wounds. In other countries in Latin and South America the plant is widely used for its antibacterial properties for numerous infectious conditions and bacterial infections. In Africa, ageratum is used to treat fever, rheumatism, headache, pneumonia, wounds, burns and colic. A decoction of the fresh plant is used as a hair wash, leaving the hair soft, fragrant and dandruff free. Also leaves are applied to cuts, burns and sores (styptic) and externally for body rash. They are also used against sore throat, spasms, diarrhea and epilepsy. The phytochemicals in tropical whiteweed include alkaloids (pyrrolizidine alkaloids lycopsamine and echinatine), cumarins, essential oils, flavonoids and tannins. It shows promising results for anti-inflammatory and antioxidant activity due to the flavonoid fraction. The plant contains between 0.7 - 2.0% essential oil, plus alkaloids and saponins. The whole plant is anti-inflammatory and anti-allergic. The juice of the fresh plant, or an extract of the dried plant, is used in the treatment of allergic rhinitis and sinusitis. The juice of the fresh plant is also useful in treating post-partum uterine haemorrhage. The juice of the root is antilithic. A paste of the root, mixed with the bark of Schinus wallichii, is applied to set dislocated bones.
Reference Grard, P., Homsombath, K., Kessler, P., Khuon, E., Le Bourgeois, T., Prospéri, J., Risdale, C. 2006. Oswald V.1.0: A multimedia identification system of the major weeds of rice paddy fields of Cambodia and Lao P.D.R. In Cirad [ed.]. Cirad, Montpellier, France. Cdrom. ISBN 978-2-87614-653-2. Jhansi and Ramanujam 1987; Kaul and Neelangini 1989; Ramanujam and Kalpana 1992; Kleinschimidt 1993 Lorenzi 1982; Scheffer 1990; Kalia and Singh 1993; Lam et al. 1993, Paradkar et al. 1993; Waterhouse 1993; Kshatriya et al. 1994 Institute of Tropical Agriculture, Ibadan, Nigeria.162p. Ivens G.W.(1976). East African weeds and their control. 104p. Johnson, D.E., 1997. Weeds of rice in West Africa. WARDA, Bouaké. 44p. Xuan, T.D., Shinkichi, T., Hong, N.H., Khanh, T.D., Min, C.I., 2004. Assessment of phytotoxic action of Ageratum conyzoides L. (billy goat weed) on weeds. Crop Prot. 23, 915-922. Marlks and Nwachuku 1986; Ladeira et al. 1987
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