Ageratina adenophora (Spreng.) R.M.King & H.Rob., Asteraceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Other Latin names:  Eupatorium adenophorum Spreng.; Eupatorium glandulosum Michx.; Eupatorium trapezoideum Kunth

Common name(s): [more details]

Chinese: po huai cao

English: Mexican devil, catweed, croftonweed, hemp agrimony, pamakani, sticky agrimony, sticky snakeroot, white thoroughwort

Hawaiian: Maui pāmakani, pāmakani haole

Habit:  herb

Description:  "Perennial coarse herbs to 1.5 m tall; stems often purple, terete, erect, glandular puberulent. Leaves opposite, median ones larger, ovate-deltoid, 7-10 cm long, 4-7 cm wide, apex acuminate, base obtuse to very broadly cuneate or truncate, sparsely pilose on both surfaces, 3-nerved, margins crenate, petiole 4-5 cm long, upper leaves gradually smaller toward inflorescence. Inflorescence of loose compound corymbs, heads ca. 6.5 mm long, 6 mm in diameter, peduncle 8-14 mm long, densely pubescent; involucre cylindric, ca. 3-4 mm long; bracts ca. 25, 3 or 4 seriate, outer ones narrowly lanceolate, inner ones narrowly oblong, apex acute, base obtuse, margins membranaceous, ciliate; florets ca. 70-80, white; receptacle glabrous, areolate. Achenes black, 1.5 mm long, 5-angular, glabrous. Pappus of 8-10 bristles, ca. 3.5 mm long"  (Digital Flora of Taiwan).

"Malodorous subshrubs; stems often purple, erect, usually 5-15 dm long, unbranched to branched, densely glandular puberulent and puberulent.  Leaves darker on upper surface, rhombic to deltate, 4-15 cm long, 1-6 (-8) cm wide, margins coarsely serrate, petioles usually 1-6 cm long.  Inflorescences strictly erect; involucral bracts 3-5 mm long, glandular puberulent; corollas white, ca. 3 mm long.  Achenes reddish brown, ca. 1.5 mm long." (Wagner et al., 1999; p. 254).

Description from the Flora of China online.
Description from the Flora of North America online.

Habitat/ecology:  "Dry to wet forests, river banks, swampy sites, grassland, disturbed places.  Dense stands eliminate native vegetation and prevent the regeneration of native plants"  (Weber 2003; p. 28).  "A highly invasive plant, tolerant of a wide range of conditions, common on roadsides and bushland edges, along watercourses, creeks, and in wetlands. Forms dense stands, prefers moist, nutrient-rich soil, is common in disturbed areas.  Capable of infesting intact bushland and displacing native plants; an increasing problem"  (Weeds of Blue Mountains bushland).

In Hawai‘i, "naturalized from relatively dry areas to wet forest, 600-2,000 m" (Wagner et al., 1999; p. 254). 

Propagation:  Seed.  "Seed production is enormous - 10,000 to 100,000 per year when mature. The seeds are very small, light, brown to black, with a 4mm "parachute" of white hairs, mid to late spring. Germination rates are high.  Seed is dispersed by wind and water over long distances, and is also moved by vehicles and machinery, and in clothing, soil and stockfeed. Also spread by garden dumping"  (Weeds of Blue Mountains bushland).

Native range:  Mexico (Wagner et al., 1999; p. 254); also cultivated and naturalized (GRIN).

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Australia (Pacific offshore islands) Lord Howe Island	Lord Howe Island	introduced	Pickard, J. (1984) (p. 205)
Australia (Pacific offshore islands) Lord Howe Island	Lord Howe Island	introduced invasive	Orchard, Anthony E., ed. (1994) (p. 18) "A Central American adventive which is invading open areas in the forest and should be urgently controlled". Vouchers cited: G. Uhe 1284 (K), L.A.S. Johnson & A.N. Rodd 1307 (NSW), P.S. Green 1969 (K), R.D. Hoogland 8730 (NSW), J. Pickard 2766 (NSW)
French Polynesia Society Islands	Tahiti Island	introduced invasive	Welsh, S. L. (1998) (p. 69) Voucher cited: BRY 24873
State of Hawaii Hawaiian Islands	Kaua‘i Island	introduced	Wester, Lyndon (1992) (p. 127)
State of Hawaii Hawaiian Islands	Lāna‘i Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 254-255)
State of Hawaii Hawaiian Islands	Maui Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 254-255)
State of Hawaii Hawaiian Islands	Moloka‘i Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 254-255) Voucher cited: Rock 6133 (BISH)
State of Hawaii Hawaiian Islands	O‘ahu Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 254-255)
Philippines Philippine Islands	Philippine Islands		Waterhouse, D. F. (1993) (p. 63)
Philippines Philippine Islands	Philippine Islands	introduced invasive	U.S. Dept. Agr., Agr. Res. Serv. (2013) Naturalized

Pacific Rim
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Australia Australia (continental)	New South Wales	introduced invasive	Harley, Barbara (2009)
Australia Australia (continental)	Australia (continental)	introduced invasive	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Australia Australia (continental)	Queensland	introduced invasive	Queensland Herbarium (2002) (p. 1)
Cambodia Cambodia	Cambodia (Kingdom of)	introduced invasive	U.S. Dept. Agr., Agr. Res. Serv. (2013) Naturalized
China China	China (People's Republic of)	introduced invasive	Zhengyi, Wu/Raven, Peter H./Deyuan, Hong (2013) "Wet places or roadsides on slopes, forest margins; 900-2200 m. Introduced and naturalized".
China China	China (People's Republic of)	introduced invasive	Li-ying, Li/Ren, Wang/Waterhouse, D. F. (1997) (pp. 172, 178)
Indonesia Indonesia	Indonesia (Republic of)		Waterhouse, D. F. (1993) (p. 63)
Mexico Mexico	Mexico (United Mexican States)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Negara Brunei Darussalam Brunei	Brunei (Negara Brunei Darussalam)		Waterhouse, D. F. (1993) (p. 63)
New Zealand New Zealand	New Zealand (country)	introduced invasive	Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. (1988) (p. 205) "Usually forest margins and clearings, waste places, scrubland, streamsides, rarely in swamps".
Taiwan Taiwan Island	Taiwan Island	introduced	Ching-I Peng, ed. (2013)
Thailand Thailand	Thailand (Kingdom of)		Waterhouse, D. F. (1993) (p. 63)
United States (west coast) United States (west coast states)	USA (California)	introduced invasive	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
Vietnam Vietnam	Vietnam (Socialist Republic of)	introduced invasive	U.S. Dept. Agr., Agr. Res. Serv. (2013) Naturalized

Comments:  A declared noxious weed in the United States.

Control: 

Physical: "May be controlled by slashing, followed by ripping or plowing, then sowing desirable pasture species"  (Motooka et al., 2003).  "Dig or pull out small infestations. Expose roots"  (Weedbusters New Zealand).

Chemical: "Herbicides used to control this plant include glyphosate, 2,4-D amine, dicamba and MCPA, or triclopyr, applied in late summer when the plant is actively growing"  (Weber, 2003; p. 28). Susceptible to hormone-type herbicides and glyphosate"  (Motooka et al., 2003).

"1. Weed wipe (all year round): glyphosate (333ml/L); or metsulferon-methyl 600g/kg (2g/L).
2. Spray: glyphosate (20ml/L + penetrant). 
3. Spray: metsulferon-methyl 600g/kg (20g/100L (spraygun) or 5g/10L (knapsack)). Add penetrant in winter. Spray lightly, not to run off"  (Weedbusters New Zealand).

Biological:  "Successful biological control has been achieved in Hawai‘i by the introduction of the Trypetid gallfly, Procecidochares utilis, a species which has also caused considerable mortality in parts of Australia, South Africa, New Zealand and India" (Cronk & Fuller, 2001; p. 134).  In Hawai‘i, "no quantitative evaluations are available, but the fungus Entyloma compositarum (Basidiomycetes: Ustilaginales) is considered effective. Fungal infestation of plants during wet periods coupled with the impact of previously introduced insects has resulted in other plants invading monotypic stands and in some cases replacing them"  (Smith et al., 2002; p. 98).