Description: "Annual herbs. Stems erect, 30-60 cm tall, hispid, branched, somewhat aromatic. Leaves petiolate, ovate, 5-13 cm long (including petiole 0.3-5 cm, apex acute, base truncate to rounded, rarely cordate, margins crenate. Heads to 6 mm across, in dense small terminal corymbs of 8-15 heads. Involucres campanulate, bracts 2-3 seriate, linear, subequal, acute, sparsely pilose outside. Flowers many (60-75), pale blue or white; corollas tubular, 1-1.5 mm long, limb 5-cleft. Achenes linear-oblong, black, 5-angled; pappus of 5 short scales, scales often serrate basally, ending in a long awn" (Digital Flora of Taiwan).
"Erect herb; young stems pubescent; leaves ovate or rhombic-ovate, acute at apex, acute to obtuse or subcordately rounded at base, pubescent on both surfaces, glandular dorsally, 2-10 cm long, 1-56 cm wide, on petiole 1-5 cm long; heads corymbose 4-6 mm long; involucre subglabrous, bracts acute-acuminate, 3 mm long; florets about 75 per head; corolla about 1 mm long, white or blue-purplish, included in the involucre; style-branches exserted, achenes 1.5-2 mm long, nearly glabrous" (Stone, 1970; p. 580).
Habitat/ecology: "Billygoat weed is a prolific ephemeral herb... It occurs as a major to intermediate weed of frequently-disturbed areas, such as vegetables and other cultivated crops, pastures (especially when overgrazed), plantations, orchards and roadsides throughout the region. It thrives best in rich, moist, mineral soils with high air humidities, and tolerates shade. The drier and less fertile conditions of atoll agriculture do not suit the plant so well; it is only a minor weed in Niue and appears to be absent from other atolls" (Swarbrick, 1997). "Common as a weed in sunny, disturbed places and croplands" (Whistler, 1988; p. 9). "A weed in many crops in the tropics and subtropics. Displaces forages in humid pastures and understory plants in disturbed forests. Seeds reportedly stick in the throats of livestock and can choke and kill them" (Motooka et al., 2003).
In Hawaii, "a widespread and often common weed, from sea level to at least 1,300 m (Wagner et al., 1999; p. 255). In Fiji, occasionally cultivated but most often seen in Fiji as an abundantly naturalized weed at elevations from near sea level to about 950 m in clearings, cultivated areas, grassland, and forest, often along trails and roads" (Smith, 1991; p. 296). Not common in Niue (Sykes, 1970). Moist uplands in the Galápagos Islands (McMullen, 1999; p. 271). In Guam, "a weed of waste ground" (Stone, 1970; p. 580). In New Guinea, "a common weed of roadsides, cultivation, waste land, plantations and pasture. From sea level to about 2000 m" (Henty & Pritchard, 1975; p. 63). In Tonga, "a frequent plantation and waste-area weed" (Yuncker, 1959; p. 266).
Propagation: Seed. "It may produce 40,000 seeds per plant and in some areas one-half of the seeds will germinate shortly after they are shed. Seeds are mainly spread by wind and water and will germinate under a wide range of conditions" (Holm et al., 1977; p. 148).
Native range: Central and South America (Wagner et al., 1999; p. 255), now a world-wide weed.
Taxon name on voucher: Ageratum conyzoides L.
Taxon name on voucher: Ageratum conyzioides L.
Voucher cited: Moseley s. n.
From sea level to about 2000 m.
A common weed in open waste places from sea level to an altitude of 2,000 m.
Anhui, Fujian, Guangdong, Guangxi, Guizhou, Hainan, Henan, Jiangsu, Jiangxi, Nanhai Zhudao, Shaanxi, Sichuan, Yunnan; only cultivated in Hebei and Zhejiang.
"Valleys, forests, forest margins on slopes, riversides, grasslands, field margins. Cultivated and naturalized".
"A common weed in waste areas and fields from low to middle elevations throughout Taiwan".
Physical: "Germination is prevented by mulches if they are thick enough and left undisturbed. Susceptible to hand weeding, chipping and cultivation under dry conditions, but stems may root if left in contact with moist soil. Unpalatable to stock. Can be controlled by competition from leafy crops, such as cassava and sweet potato, but it is fairly shade-tolerant. Dislikes dry air and soil conditions" (Swarbrick, 1997). "Goats with control ageratum (An Peischel)" (Motooka et al., 2003).
Chemical: "Susceptible to: 1) residual herbicides, including diuron, atrazine, acifluorfen, ametryne, bromacil and karbutilate at standard rates; 2) translocated herbicides, including 2,4-D, glyphosate and fluroxypyr at standard rates; 3) contact herbicides, including diquat and paraquat at standard rates. Probably susceptible to most herbicides suitable for controlling broad-leaved plants" (Swarbrick, 1997). "Sensitive to 2,4-D and probably to all hormone-type dicot killers" (Motooka et al., 2003).
Biological: Waterhouse (1994, pp. 13-16) lists the natural enemies of the species.