Datasheet

Enhanced

23 July 2024

Mikania micrantha (bitter vine)

Author: Michael DayAuthors Info & Affiliations

Publication: CABI Compendium

34095

https://doi.org/10.1079/cabicompendium.34095

Datasheet Types: Invasive Species, Pest, Host Plant, Natural Enemy

PDF/EPUB

Abstract

This datasheet on Mikania micrantha covers Impact, Identity, Overview, Associated Diseases, Pests or Pathogens, Distribution, Dispersal, Hosts/Species Affected, Vectors & Intermediate Hosts, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control and Further Information.

Identity

Preferred Scientific Name: Mikania micrantha Kunth
Preferred Common Name: mile-a-minute
Other Scientific Names: Eupatorium denticulatum Vahl; Eupatorium orinocense (Kunth) Gómez de la Maza; Eupatorium orinocense (Kunth) M.Gómez; Eupatorium orinocense var. batataefolium (DC.) M.Gómez; Eupatorium orinocense var. tamoides (DC.) M.Gómez; Kleinia alata G. Meyer; Mikania alata (G.Mey.) DC.; Mikania cissampelina DC.; Mikania denticulata (Vahl) Willd.; Mikania glechomifolia Sch.Bip. ex Baker; Mikania micrantha (Hieron.) B.L.Rob.; Mikania micrantha f. hirsuta (Hieron.) B.L.Rob.; Mikania micrantha var. micrantha; Mikania orinocensis Kunth; Mikania scandens var. cynanchifolia Hook. & Arn. ex Baker; Mikania scandens var. sagittifolia Hassl.; Mikania scandens var. subcymosa (L.) Wild., 1876; Mikania scandens var. umbellifera (Gardner) Baker; Mikania sinuata Rusby; Mikania subcrenata Hook. & Arn.; Mikania subcymosa Gardner; Mikania umbellifera Gardner; Mikania variabilis Meyen & Walp.; Willoughbya cissampelina (DC.) Kuntze; Willoughbya micrantha (Kunth) Rusby; Willoughbya scandens var. orinocensis (Kunth) Kuntze; Willoughbya variabilis (Meyen & Walp.) Kuntze
International Common Names: English
American rope
Chinese creeper
climbing hempweed
Mikania vine
mile-a-minute weed; French
liane Américaine; Spanish
guaco
wappe
Local Common Names: American Samoa
fue saina; Cook Islands
po kutekute; Fiji
ovaova
usuvanua
wabosucu
wabutako
wambosuthu
wambosuvu
wandamele; Germany
Sommer-Efeu; India
japani habi; Indonesia
sembang rambat; Malaysia
cheroma
ulam tikas; Micronesia, Federated states of
selmwadang
selmwadang; Niue
fou laina
fue saina; Palau
teb el yas; Peru
camotille; Saint Lucia
kacho; Samoa
fue saina; Solomon Islands
kwalo kalialo
kwalo kauburu
EPPO code: MIKMI (Mikania micrantha)

Pictures

Habit of Mikania micrantha (bitter vine) showing rampant growth inside and outside of a shade house. Homestead, Florida, USA. December 2010. — Habit
Mikania micrantha (bitter vine); Habit, showing rampant growth inside and outside of a shade house. Homestead, Florida, USA. December 2010.
©Andrew Derksen/USDA-APHIS/Bugwood.org - CC BY-NC 3.0 US

Leaves of Mikania micrantha (bitter vine). Simple, opposite, glabrous, thin, broadly ovate, shallowly or coarsely toothed, triangular or ovate, tip acuminate, blade 4-13 x 2-9 cm. — Leaves
Mikania micrantha (bitter vine); Leaves simple, opposite, glabrous, thin, broadly ovate, shallowly or coarsely toothed, triangular or ovate, tip acuminate, blade 4-13 x 2-9 cm.
©Colin Wilson

Habit of Mikania micrantha (bitter vine) invading forest in India. — Invasive habit
Mikania micrantha (bitter vine); Habit, invading forest in India.
©Chris Parker/Bristol, UK

Climbing shoots of Mikania micrantha (bitter vine). Bhutan. — Habit
Mikania micrantha (bitter vine); Climbing shoots. Bhutan.
©Chris Parker/Bristol, UK

Inflorescence of Mikania micrantha (bitter vine). A corymbose panicle with subcymose branches, 3-6 cm long by 3-10 cm wide; flowers small, white or cream coloured. Indonesia. — Flowering habit
Mikania micrantha (bitter vine); Inflorescence a corymbose panicle with subcymose branches, 3-6 cm long by 3-10 cm wide; flowers small, white or cream coloured. Indonesia.
©P.J. Terry/LARS

Habit of Mikania micrantha (bitter vine). A vigorous, fast-growing, perennial, creeping or twining plant with numerous cordate leaves, and numerous large, loose heads of white or cream-coloured flowers that produce many seeds. — Habit
Mikania micrantha (bitter vine); Habit. A vigorous, fast-growing, perennial, creeping or twining plant with numerous cordate leaves, and numerous large, loose heads of white or cream-coloured flowers that produce many seeds.
©Matthew Cock

Florets of Mikania micrantha (bitter vine) is white or greenish, fragrant; corolla mostly white, tubular, 2.5-4 mm long; involucral bracts 4, oblong to obovate, 2-4 mm long, acute, green, with one additional smaller bract 1-2 mm long. — Flowers
Mikania micrantha (bitter vine); Florets white or greenish, fragrant; corolla mostly white, tubular, 2.5-4 mm long; involucral bracts 4, oblong to obovate, 2-4 mm long, acute, green, with one additional smaller bract 1-2 mm long.
©Colin Wilson

Habit of Mikania micrantha (bitter vine) bursting into seed early in winter at an abandoned nursery. Homestead, Florida, USA. December 2010. — Habit, seeding
Mikania micrantha (bitter vine); Habit, bursting into seed early in winter at an abandoned nursery. Homestead, Florida, USA. December 2010.
©Andrew Derksen/USDA-APHIS/Bugwood.org - CC BY-NC 3.0 US

Symptoms of septoria leaf spot (Septoria mikaniae-micranthae), a natural enemy of Mikania micrantha (bitter vine), showing patchy damage on leaves. — Natural enemy
Mikania micrantha (bitter vine); Natural enemy of M. micrantha, septoria leaf spot (Septoria mikaniae-micranthae) - symptoms on leaves show patchy damage.
©Andrew Derksen/USDA-APHIS/Bugwood.org - CC BY-NC 3.0 US

A leaf of Mikania micrantha (bitter vine) with fungal lesions caused by its natural enemy. — Natural enemy
Mikania micrantha (bitter vine); Natural enemy, a leaf with fungal lesions.
©CABI BioScience

Diseases Table

Summary of Invasiveness

Mikania micrantha is a fast-growing vine, native to Central and South America. It was intentionally introduced into numerous countries, either as a cover crop or soil conservation, while being accidentally introduced into other countries. M. micrantha has since become a major weed in Asia and the Pacific and it is still extending its range. It has not yet been recorded in Africa. Once established, M. micrantha can quickly smother other vegetation, including native trees, plantation species and agricultural crops, killing plants and/or decreasing yield and biodiversity. In Nepal, the vulnerable greater one-horned rhinoceros is under threat as M. micrantha outcompetes plant species on which it browses. Control of M. micrantha is difficult as it can grow up and over preferred species, limiting the use of herbicides, produces a large number of seeds, can readily shoot from runners and suckers and can regenerate from stem fragments. This species has been the target of a biological control programme in numerous countries.

Taxonomic Tree

Notes on Taxonomy and Nomenclature

The genus Mikania is the largest genus in the tribe Eupatorieae within the family Asteraceae and contains species primarily native to tropical and temperate America (Day et al., 2016). M. micrantha is a New World species whose full distribution in the Old World has only recently been fully realized. In much of the earlier literature, it was mistakenly referred to as M. scandens or M. cordata. Although Holm et al. (1991) state that M. cordata is "by far the most important weed of the three", this reference is now known to be incorrect and many of the records for the distribution of M. cordata in early literature refer to M. micrantha.

Studies of karyotypes and chromosome morphology of M. micrantha, M. glomerata, M. trinervis (from Londrina and Parana, Brazil) and M. cordifolia, M. laevigata and M. viminea (from Porto Alegre, Rio Grande do Sol, Brazil), have indicated that M. micrantha is a tetraploid with 2n=72, M. viminea a tetraploid with 2n=68, M. laevigata a diploid with 2n=38 and M. cordifolia a diploid with 2n=34. The other two species, M. glomerata and M. trinervis are also diploids. All species except M. micrantha had one long pair of chromosomes with a secondary constriction in the long arms, whereas M. micrantha had two pairs of long chromosomes. This suggested an evolutionary trend towards formation of aneuploid series and polyploidy (Ruas and Ruas, 1987).

Plant Type

Perennial

Seed / spore propagated

Vegetatively propagated

Vine / climber

Description

Mikania micrantha is a vigorous, fast-growing, perennial, creeping or twining plant, with numerous cordate leaves and numerous large, loose heads of white or cream-coloured flowers that produce many seeds. This plant can climb and smother other vegetation such as plantation trees e.g. coconuts, or Hevea brasiliensis (rubber) trees as tall as 25 m.

Mikania micrantha is a much-branched, scrambling, slender-stemmed vine; stems herbaceous to semi-woody, branched, ribbed, sparsely pubescent or glabrous; leaves simple, opposite, glabrous, thin, broadly ovate, shallowly or coarsely toothed, triangular or ovate, tip acuminate, blade 4-13 cm long, 2-9 cm wide, 3-7 nerved; at the junction of the petioles with the nodes, unusual nodal appendages, membranous, up to 5 mm long; petioles tendriliform, 2-9 cm long; inflorescence a corymbose panicle with subcymose branches, 3-6 cm long by 3-10 cm wide; flowers small, white or cream-coloured, actinomorphic, 4.5-6 mm long, in leaf axils or on terminal shoots; florets white or greenish, fragrant; corolla mostly white, tubular, 2.5-4 mm long; involucral bracts 4, oblong to obovate, 2-4 mm long, acute, green, with one additional smaller bract 1-2 mm long; pappus (calyx) of 32-38 barbellate, capillary bristles, 2-3 mm long; stamens attached by their anthers, these exserted, with a triangular-ovate apical appendage as long as broad or longer and rounded or rarely emarginate or subsagittate at base; ovary inferior, the style base glabrous; fruit an achene that is somewhat flattened, elliptic, 4-ribbed with short, white hairs along the ribs, with a tuft of white pappus at the summit, glandular, 1.2-1.8 mm long, dark grey to black (Parham, 1958; 1962; Adams and Proctor, 1972; Nair, 1988; Holm et al., 1991).

Species Vectored

Distribution

Mikania micrantha is native to South and Central America, where it is widespread but is not considered a weed (Holm et al., 1991; Barreto and Evans, 1995). This species was intentionally introduced into some countries in the Asia-Pacific region and has since been reported in 20 countries and/or territories in the Pacific and most countries in Southeast Asia. However, in some countries, including Australia, China and India, its distribution within the country is limited, most probably by climate and altitude (Day et al., 2016).

Mikania micrantha was often mistakenly referred to as M. scandens or M. cordata (Adams and Proctor, 1972; Parker, 1972; Holm et al., 1991; Ismail and Mah, 1993). Most of the records in Holm et al. (1991) for M. cordata and M. scandens in Asia, almost certainly refer to M. micrantha, while those for M. cordata in West Africa are probably correct. Conversely, most of the records for M. micrantha in mainland Africa cited in EPPO (2023) probably relate to the indigenous M. cordata. The record of M. micrantha in Mauritius may also be correct. The occurrence of true M. micrantha in mainland Africa is yet to be confirmed.

Distribution Map

Distribution Table

History of Introduction and Spread

Mikania micrantha was first reported in Asia in 1884 in Hong Kong, where it was growing in the Hong Kong Zoological and Botanical Gardens (Wang et al., 2003). M. micrantha was reported in mainland China in 1910 (Zhang et al., 2004) and India in 1918 (Choudhury, 1972), although there are reports that M. micrantha was introduced into India again during World War II (e.g. Puzari et al., 2010). M. micrantha was later recorded in Indonesia in 1949 (Wirjahardja, 1976), Malaysia in the 1950s (Ismail, 2001) and Taiwan in the 1970s (Tripathi et al., 2012).

Mikania micrantha was first reported in the Pacific in Fiji, in 1907 (Knowles, 1907). It was later reported in Western Samoa in 1924, American Samoa in 1938, Vanuatu and Niue by 1943 (PIER, 2015), Papua New Guinea in 1951 (ACP Forenet, 2006), Guam in 1963 (PIER, 2015), Tonga in 1979 (Waterhouse and Norris, 1987), the Solomon Islands in 1988, the Cook Islands in 1991, Northern Mariana Islands pre 2000, the Federated States of Micronesia in 2000 (PIER, 2015) and in Kiribati in 2012 (A. Gunua, The Secretariat of the Pacific Community, personal communication, 2013). A list of all countries in the Pacific where M. micrantha has been reported is presented in Day et al. (2016). M. micrantha was first found in north Queensland, Australia in 1998 and is the focus of a national cost-share eradication programme (Brooks et al., 2008).

Mikania micrantha was intentionally introduced into numerous countries. It was introduced into Taiwan for soil conservation, into India and Indonesia as ground cover and into Malaysia as a non-leguminous ground cover for plantations of Hevea brasiliensis (rubber) (Ismail, 2001). It may have spread naturally from these countries into neighbouring countries. In the Pacific, the cause of spread into many countries is not known. It is possible that it was deliberately introduced into some countries as a treatment of cuts or as a herbal medicine, while it was accidentally introduced into others in packing material.

Risk of Introduction

Mikania micrantha produces vast quantities of seed which can be spread by wind and to a lesser extent, water. However, the plant can also be spread easily by vehicles and machinery, on animals and people, or on belongings, via stem fragments, root stocks or the light weight seed which contain a pappus. A piece of stem with a single node is sufficient to resprout. In Papua New Guinea, it is believed M. micrantha spread along forestry tracks by logging equipment (Holm et al., 1991; Day et al., 2012a).

Vehicles and equipment moving through infested areas should be cleaned before travelling to uninfested areas. M. micrantha is classified as a Federal Noxious Weed in the USA (Westbrooks, 1989) and border clearance personnel with the US Department of Agriculture have intercepted M. micrantha as a contaminant of medicinal herbs from Mexico. Seeds of several species of Mikania have also been intercepted as a hitchhiker on a truck entering the USA from Mexico (Westbrooks, 1989). Seeds of M. micrantha are the most intercepted seeds coming into Hawai’i on military vehicles from Guam. M. micrantha has been given a high risk score of 25 by a PIER risk assessment for the Pacific region (PIER, 2016).

Means of Movement and Dispersal

Natural Dispersal

Dispersal of M. micrantha is mainly by wind, but water dispersal is possible.

Vector Transmission

Seeds of M. micrantha can be dispersed into new locations by adhering to animals, machinery and human possessions.

Intentional Introduction

Mikania micrantha was intentionally introduced into numerous countries. For example, it was introduced into Taiwan for soil conservation, into India and Indonesia as ground cover and into Malaysia as a non-leguminous ground cover for plantations of Hevea brasiliensis (Ismail, 2001).

Accidental Introduction

The seeds of M. micrantha may be carried on any article that is transported through an area where the weed grows. Vehicles and equipment moving through areas infested with M. micrantha are likely carriers and should be cleaned before travelling long distances to avoid the spread of the weed.

Pathway Causes

Pathway cause	Notes	Long distance	Local
Animal production	Rarely; Stock tend not to eat it but seeds can be transported on fur		Yes
Crop production	Infrequent; Fragments can get caught up in harvests	Yes	Yes
Disturbance	Frequent; disturbance allows the opportunity of plants to become established		Yes
Garden waste disposal	Frequent; plants cleared can be moved for disposal but fragments can set roots and new plants can become established		Yes
Forestry	Frequent; Particularly via seeds on machinery	Yes	Yes
Hitchhiker	Frequent; Particularly via seeds on clothing, machinery, possessions	Yes	Yes
Horticulture	Not so common now, as people are more aware of the negative impacts of the weed	Yes	Yes
Medicinal use	Not so common now, as people are more aware of the negative impacts of the weed	Yes	Yes
Military movements	Frequent; Particularly via seeds on machinery	Yes	Yes
People sharing resources	Not so common now. Has been used as packing material but people more aware of the negative impacts of the weed	Yes	Yes
Self-propelled	Frequent; Particularly via seeds	Yes	Yes
Timber trade	Frequent; Particularly via seeds on machinery	Yes	Yes

Pathway Vectors

Pathway vector	Notes	Long distance	Local
Aircraft	Not so frequent now	Yes
Bulk freight or cargo	Not so frequent now	Yes
Clothing, footwear and possessions	Frequent	Yes	Yes
Containers and packaging - non-wood	Frequent	Yes	Yes
Containers and packaging - wood	Frequent	Yes	Yes
Debris and waste associated with human activities	Frequent		Yes
Floating vegetation and debris	Frequent		Yes
Land vehicles	Frequent	Yes	Yes
Livestock	Frequent		Yes
Machinery and equipment	Frequent	Yes	Yes
Mulch, straw, baskets and sod	Frequent	Yes	Yes
Plants or parts of plants	Frequent		Yes
Soil, sand and gravel	Frequent	Yes	Yes
Water	Frequent		Yes
Wind	Frequent	Yes	Yes

Plant Trade

Plant parts liable to carry the pest in trade/transport	Pest stages	Borne internally	Borne externally	Visibility of pest or symptoms
Growing medium accompanying plants	Weeds/Seeds	No	Yes	Pest or symptoms usually invisible

Wood Packaging

Wood Packaging liable to carry the pest in trade/transport	Timber type	Used as packing
Loose wood packing material		Yes

Wood Packaging not known to carry the pest in trade/transport
Non-wood
Processed or treated wood
Solid wood packing material without bark

Hosts/Species Affected

Mikania micrantha is a serious weed of agriculture, affecting over 20 species, including plantation trees such as species of Citrus spp., Theobroma cacao (cocoa), Coffea spp., Camellia sinensis (tea), Tectona grandis (teak), Hevea brasiliensis (rubber), Elaeis guineensis (African oil palm), Cocos nucifera (coconut) and Bambusa vulgaris (common bamboo). It is also a serious weed of Musa spp. (bananas), Manihot esculenta (cassava), Zingiber officinale (ginger), Carica papaya (papaya), Ananas comosus (pineapple), Litchi chinensis (lychee), Saccharum officinarum (sugar cane), Ipomoea batatas (sweet potato), Colocasia esculenta (taro) and Dioscorea spp. (yams), especially in warm, moist locations or where soil fertility is high (Cock, 1982; Waterhouse and Norris, 1987; Holm et al., 1991; Abraham et al., 2002a; Macanawai et al., 2010; Day et al., 2012a; 2016).

Host Plants and Other Plants Affected

Host	Family	Host status	References
Ananas comosus (pineapple)	Bromeliaceae	Main	Willis et al. (2008)
Areca catechu (betel nut)	Arecaceae	Main	Willis et al. (2008)
Artocarpus altilis (breadfruit)	Moraceae	Main	GISD (2024)
Bambusa vulgaris (common bamboo)	Poaceae	Main
Camellia sinensis (tea)	Theaceae	Main	Puzari et al. (2010), Shen et al. (2013)
Carica papaya (pawpaw)	Caricaceae	Main	Day et al. (2012a)
Citrus		Main	Shen et al. (2013)
Cocos nucifera (coconut)	Arecaceae	Main	Waterhouse and Norris (1987), GISD (2024)
Coffea (coffee)	Rubiaceae	Main	Abraham and Abraham (2005)
Colocasia esculenta (taro)	Araceae	Main	Day et al. (2012a), Macanawai et al. (2012b)
Dioscorea alata (yam)	Dioscoreaceae	Main	Holm et al. (1991)
Elaeis guineensis (African oil palm)	Arecaceae	Main	Waterhouse and Norris (1987), GISD (2024)
Hevea brasiliensis (rubber)	Euphorbiaceae	Main	Teoh et al. (1985), GISD (2024)
Ipomoea batatas (sweet potato)	Convolvulaceae	Main	Holm et al. (1991)
Litchi chinensis (lichi)	Sapindaceae	Main	M.D. Day pers. comm. (2013)
Manihot esculenta (cassava)	Euphorbiaceae	Main	Abraham and Abraham (2005), Macanawai et al. (2012b)
Musa (banana)	Musaceae	Main	GISD (2024), Macanawai et al. (2010)
Oryza sativa (rice)	Poaceae	Main	Kaur et al. (2012)
Psidium guajava (guava)	Lithomyrtus	Main	Willis et al. (2008)
Saccharum officinarum (sugarcane)	Poaceae	Main	Macanawai et al. (2012b), Shen et al. (2013)
Tectona grandis (teak)	Lamiaceae	Main	Muraleedharan and Anitha (2000)
Theobroma cacao (cocoa)	Malvaceae	Main	Teoh et al. (1985), GISD (2024)
Zingiber officinale (ginger)	Zingiberaceae	Main	Kaur et al. (2012)

Vectors and Intermediate Hosts

Vector	Source	Reference	Group
Mammals			Other

Growth Stages

Fruiting stage

Flowering stage

Seedling stage

Vegetative growing stage

Similarities to Other Species/Conditions

Mikania is a genus of vines, with most of the 430 species being native to tropical America. The three most common species are M. cordata, M. scandens and M. micrantha and are often misidentified as each other. These species may be generally distinguished by the following characteristics (Holm et al., 1991).

Mikania micrantha: pappus bristles 32-38, white, corolla white, head length 4.5-6 mm, nodal appendages membranous. Distributed throughout tropical and central America.

Mikania cordata: pappus bristles 40-45, reddish, corolla white, head length 7-7.5 mm, nodal appendages form furry ridges not membranous. Distributed throughout Southeast Asia and Africa.

Mikania scandens: pappus bristles 30-35, usually whitish, corolla pale purple, head length 5-7 mm. Distributed in eastern North America.

In Taiwan, M. micrantha has been difficult to distinguish from the native M. cordata and a molecular technique has been developed to differentiate between the two species (Chen et al., 2002).

Mikania micrantha possesses unique semi-translucent enations between the petioles at the nodes of young vegetative shoots (similar to stipules). These structures are very unusual in Compositae. They wither on older shoots and are not seen on flowering branches (Adams and Proctor, 1972). Differences in the form of these enations can help to distinguish M. micrantha from M. cordata.

Habitat

Mikania micrantha is a tropical vine that can grow in a wide range of habitats. It is usually found in damp, lowland clearings or open areas, where there is adequate temperate, light and rainfall or soil moisture. M. micrantha can tolerate flooding or shallow water, which may promote its invasiveness (Day et al., 2016; Yue et al., 2019). It also grows along streams and roadsides, along edges of forests and forest plantations, along fence-lines, in pastures and wastelands and on and among tree crops such as rubber (Hevea brasiliensis), oil palm (species of Elaeis), cocoa (Theobroma cacao), tea (Camellia sinensis), coffee (species of Coffea), fruit trees and cash crops such as taro (Colocasia esculenta), pineapples (Ananas comosus) and cassava (Manihot esculenta) (Parham, 1958; 1962; Adams and Proctor, 1972; Waterhouse and Norris, 1987; Holm et al., 1991; Day et al., 2012a). It may be common in areas affected by slash and burn agriculture (Rawat, 1997). In Singapore, it spreads on coastal reclaimed sand-filled areas (Lee et al., 1997). M. micrantha rarely penetrates undisturbed forests, where light may be a limiting factor (Holm et al., 1991; Day et al., 2016).

Habitat List

Category	Sub-Category	Habitat	Presence	Status
Terrestrial	Terrestrial - Managed	Cultivated / agricultural land	Present, no further details	Harmful (pest or invasive)
Terrestrial	Terrestrial - Managed	Managed forests, plantations and orchards	Present, no further details	Harmful (pest or invasive)
Terrestrial	Terrestrial - Managed	Disturbed areas	Present, no further details	Harmful (pest or invasive)
Terrestrial	Terrestrial - Managed	Rail / roadsides	Present, no further details
Terrestrial	Terrestrial - Managed	Urban / peri-urban areas	Present, no further details	Harmful (pest or invasive)
Terrestrial	Terrestrial - Natural / Semi-natural	Natural forests	Present, no further details	Harmful (pest or invasive)
Terrestrial	Terrestrial - Natural / Semi-natural	Riverbanks	Present, no further details	Harmful (pest or invasive)
Terrestrial	Terrestrial - Natural / Semi-natural	Managed grasslands (grazing systems)	Present, no further details	Harmful (pest or invasive)

Biology and Ecology

Genetics

Brazilian populations of M. micrantha show little morphological variation. However, there is much chromosome polymorphism. Of the 12 populations investigated, eight were diploid (2n=36 and 42) and four tetraploid (2n=72) (Maffei et al., 1999).

Physiology and Phenology

According to some studies, seedlings of M. micrantha reach 1.1 cm and have a leaf surface area of 0.3 cm² by 30 days after germination. By 54 days after germination, the plants average 6.6 cm in height and have a leaf surface area of 17.2 cm². M. micrantha will grow all year round if temperatures, light and moisture are adequate. Growth rates for M. micrantha vary in different countries. For example, 8-9 cm/day in India (Choudhury, 1972), 6-7 cm/day in China (Zhang et al., 2004), 3.3 cm/day in Papua New Guinea (Day et al., 2012b) and 2.7-3.8 cm/day in Fiji (Macanawai et al., 2012a).

Mikania micrantha takes about 5 days to develop from flower bud to full-flower, 5 days from flower to anthesis and another 5 to 7 days to produce mature seed (Hu and But, 1994). Flowering occurs during the dry season (from September to October in most Pacific island countries) and seed production takes place from November to February. In the Dongguan region in China, flowering has been recorded from October to December and fruiting from November to December (Zhang et al., 2004). Flowers tend to be self-incompatible and require pollination by wind or insects (Day et al., 2016). In Fiji, Apis mellifera (honeybees) have been reported as the most prolific visitor of M. micrantha flowers (Macanawai et al., 2018).

Reproductive Biology

Sexual reproduction of M. micrantha is by seeds. During the period of sexual reproduction, the biomass of the flowers can be 38-43% of the total plant biomass. Up to 60,000 seeds can be produced per m².However, despite the large volume of seeds produced, the seeds in the soil seed bank is relatively small, about 600 seeds m² (Macanawai et al., 2018), and are dispersed by wind, water and animals. The seeds (achenes) are very small (1000 seeds weigh 0.0892 g) and are extremely suitable for wind dispersal (Hu and But, 1994). Seed germination rates are high (up to 96%), although the percentage germination is affected by temperature, the optimum temperature being 25-30°C. Germination rate of seeds in spring is slightly higher than in autumn (80% vs 70%), suggesting that M. micrantha seeds may have an after-ripening requirement (Zhang et al., 2004). Seeds can remain viable in the soil for up to 7 years.

Mikania micrantha can readily shoot from runners and suckers and can regrow from stem fragments after manual or mechanical slashing (Dutta, 1977; Day et al., 2012a; Macanawai et al., 2015). The plant can produce adventitious roots, which can aid M. micrantha in growth and access to nutrients. This becomes a competitive advantage when gaps in vegetation appear, allowing M. micrantha to quickly establish. The production of adventitious roots can thus, increase the invasiveness of M. micrantha (Shen et al., 2021).

Environmental Requirements

Mikania micrantha has a wide altitudinal distribution, as it may grow at an elevation of 2000 m or more. In Bolivia, it has been observed at 3000 m (Holm et al., 1991). It is found between sea level and 1100 m in Malaysia and Papua New Guinea (Ismail, 2001; Day et al., 2012a), while it has been found up to 1000 m in Fiji, Vanuatu and Taiwan.

Mikania micrantha grows best where the annual average temperature is higher than 21°C and soil moisture is over 15% (Zhang et al., 2004). M. micrantha can grow in a range of soil types, from sandy loam to gravelly coarse soil and can tolerate areas of free drainage, saturated and moist areas and can tolerate a range of pH from acidic to alkaline (pH 3.6-8.3) and from infertile to highly fertile (organic material 2.29-32.85) (Ye and Zhou, 2001; Day et al., 2016).

Climate

Climate type	Status	Description
A - Tropical/Megathermal climate	Preferred	Average temp. of coolest month > 18°C, > 1500mm precipitation annually
Af - Tropical rainforest climate	Preferred	> 60mm precipitation per month
Am - Tropical monsoon climate	Preferred	< 60mm precipitation driest month but > (100 - [total annual precipitation(mm}/25])
As - Tropical savanna climate with dry summer	Tolerated	< 60mm precipitation driest month (in summer)
Aw - Tropical wet and dry savanna climate	Tolerated	< 60mm precipitation driest month (in winter)
C - Temperate/Mesothermal climate	Preferred	Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C
Cf - Warm temperate climate, wet all year	Preferred	Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer	Tolerated	Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Cw - Warm temperate climate with dry winter	Preferred	Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)

Latitude/Altitude Ranges

Latitude North (°N)	Latitude South (°S)	Altitude lower (m)	Altitude upper (m)
28	21	0	1500

Air Temperature

Parameter	Lower limit (°C)	Upper limit (°C)
Mean annual temperature (°C)	10	23
Mean maximum temperature of hottest month (°C)	13	16
Mean minimum temperature of coldest month (°C)	27	33

Rainfall Regime

Summer

Uniform

Soil Tolerances

Soil texture > Light (sands, sandy loams)

Soil texture > Medium (loams, sandy clay loams)

Soil texture > Heavy (clays, clay loams, sandy clays)

Soil reaction > Very acid (pH <4.0)

Soil reaction > Acid (pH 4.0-6.0)

Soil reaction > Neutral (pH 6.1-7.4)

Soil reaction > Alkaline (pH 7.4-9.4)

Soil drainage > Free

Soil drainage > Impeded

Soil drainage > Seasonally waterlogged

Notes on Natural Enemies

Numerous species of arthropods and pathogens have been found attacking M. micrantha in Kerala State, India. However, all the species found were either polyphagous or not sufficiently damaging to control the weed (Teoh et al., 1985; Abraham et al., 2002a).

Over 30 species of insects, mites and pathogens have been found on M. micrantha in China (Han et al., 2001) but no assessments on their impact on M. micrantha or their potential as biological control agents have been conducted. In peninsular Malaysia, the fungus Rhizoctonia solani [Thanatephorus cucumeris] has been found to be pathogenic on M. micrantha. However, it should be noted that this is a serious crop pest (Lim et al., 1987).

In Florida, USA, where M. micrantha is deemed to be invasive, 16 herbivorous arthropods were found attacking the plant, but none were considered to be monophagous. Several species have been recorded as pests, also attacking several crop species (Diaz et al., 2015).

Surveys of natural enemies of M. micrantha were conducted by CABI in the late 1970s in the native range of the weed, in Central and South America and throughout the Caribbean (Cock, 1982). Natural enemies found, included an eriophyid mite Acalitus sp., the seed-feeding weevil Apion luteirostre, the flower midge Neolasioptera sp., inflorescence-inhabiting lace bugs Teleonemia spp., cassids Omoplata spp., the weevil Pseudoderelomus baridiiformis and the thrips Liothrips mikaniae, which was considered the most promising as a biological control agent (Cock et al., 1982). An additional 20 species causing minor damage to M. micrantha were also recorded (Cock et al., 1982).

Surveys of pathogens on M. micrantha conducted by CABI in southern Brazil from 1988-1989 and 1996-1999, found 11 species, including Basidiophora montana, Mycosphaerella mikaniae-micranthae, Septoria mikaniae-micranthae, Asperisporium mikaniae [Passalora mikaniigena], A. mikaniigena, Pseudocercospora plunkettii, Cercospora mikaniicola and the rust Puccinia spegazzinii (Barreto and Evans, 1995; Evans and Ellison, 2005). Due to the high level of damage caused and its wide climatic range, P. spegazzinii was thought to be the most promising as a biological control agent (Barreto and Evans, 1995).

Waterhouse and Norris (1987) and Waterhouse (1994) have detailed earlier reviews of the natural enemies of M. micrantha.

Natural enemies

Natural enemy	Type	Life stages	Specificity	References	Biological control in
Acalitus sp.	Herbivore	Leaves Whole plant Leaves, Whole plant		Cock (1982), Winston et al. (2014)	Bangladesh, China, FSM, Guam, India, Indonesia, Lao, Malaysia, Mynmar, NMI, Palau, PNG, Philippines, Singapore, Taiwan, Thailand, Timor Leste, Vietnam
Actinote sp.	Herbivore	Leaves		Desmier de Chenon et al. (2002)	Indonesia
Apion luteirostre	Herbivore	Inflorescence		Cock (1982)
Asperisporium mikaniigena	Pathogen	Leaves		Barreto and Evans (1995)
Basidiophora montana	Pathogen	Leaves		Barreto and Evans (1995)
Cercospora mikaniicola	Pathogen	Leaves		Barreto and Evans (1995)
Desmogramma conjuncta	Herbivore	Leaves		Cock (1982)
Liothrips mikaniae	Herbivore		to species	Cock (1982)
Mycosphaerella mikaniae-micranthae	Pathogen	Leaves	to species	Barreto and Evans (1995)
Omoplata marginata	Herbivore	Leaves	to genus	Cock (1982)
Omoplata quadristilla	Herbivore	Leaves	to genus	Cock (1982)
Passalora mikaniigena	Pathogen	Leaves		Barreto and Evans (1995)
Physimerus pygmaeus	Herbivore	Leaves	not specific	Cock (1982)
Pseudocercospora plunkettii	Pathogen	Leaves		Barreto and Evans (1995)
Pseudoderelomus baridiiformis	Herbivore	Inflorescence	not specific	Cock (1982)
Puccinia spegazzinii	Pathogen	Leaves	to species	Ellison et al. (2008)	Taiwan, Cook Islands, Fiji, Papua New Guinea, Solomon Islands, Vanuatu
Septoria mikaniae-micranthae	Pathogen	Leaves		Barreto and Evans (1995)
Teleonemia sp. nr. prolixa	Herbivore	Leaves	to species	Cock (1982)

Impact Summary

Category	Impact
Environment (generally)	Negative
Economic/livelihood	Negative
Human health	Positive
Cultural/amenity	None
Animal/plant collections	None
Animal/plant products	None
Biodiversity (generally)	Negative
Crop production	Negative
Fisheries / aquaculture	None
Forestry production	Negative
Livestock production	Negative
Native fauna	Negative
Native flora	Negative
Rare/protected species	Negative
Tourism	None
Trade/international relations	None
Transport/travel	None

Impact: Economic

Mikania micrantha is an agricultural weed where it can rapidly grow and smother a large number of crops. This can result in large economic losses through a reduction in yields and an increase in costs for control of this species. For instance, in the Pearl River Delta in China, the economic losses are estimated to be as high as 8 billion RMB p.a. (Han et al., 2017).

In Papua New Guinea, M. micrantha was found to cause yield losses of greater than 30% in nearly half of survey respondents (Day et al., 2012a). In Malaysia, the girth of Hevea brasiliensis (rubber) trees in plantations with M. micrantha was found to be 27% smaller than of trees in plantations with leguminous ground cover (Watson et al., 1964). The yield of Elaeis guineensis (oil palm) infested with M. micrantha was estimated to be 20% less than crops without M. micrantha (Teoh et al., 1985). In India, M. micrantha growing over large Camellia sinensis (tea) plantations, caused a decrease in yield of 41%, through competition and disrupting the harvesting of new leaves (Puzari et al., 2010) and M. micrantha in Saccharum officinarum (sugar cane) fields in Fiji interfered with the slashing of cane (Holm et al., 1991; A. Macanawai, Department of Agriculture, personal communication, 2012).

In addition, M. micrantha has been reported to have a negative impact in terms of growth, flowering and yield, upon species of Musa (bananas), Manihot esculenta (cassava), species of Citrus, Cocos nucifera (coconut), species of Coffea (coffee), Psidium guajava (guava), Piper methysticum (kava), Litchi chinensis (lychee), Zea mays (maize), Morinda citrifolia (noni), Carica papaya (papaya), Ananas comosus (pineapples), Ipomoea batatas (sweet potato), Colocasia esculenta (taro), Tectona grandis (teak) and species of Dioscorea (yams) (Waterhouse and Norris, 1987; Holm et al., 1991; Abraham et al., 2002a; Abraham and Abraham, 2005; Macanawai et al., 2010; 2012b; Puzari et al., 2010; Day et al., 2012a, b).

Mikania micrantha can also compete with pastures, causing a decrease in livestock production (PIER, 2015). A study by Widjaja and Tjitrosoedirdjo (1991) found that the climbing habit of M. micrantha enabled it, to grow over a number of other species, such as bamboo (Bambusoideae subfamily), suppressing their growth and in some cases killing them. Numerous forest species such as Dalbergia sissoo (Indian rosewood) and Bombax ceiba (cotton tree) have also been affected from M. micrantha, causing economic loss (Sapkota, 2007).

The annual cost of controlling M. micrantha was estimated at US$9.8 million for H. brasiliensis, E. guineensis and Theobroma cacao (cocoa) crops in Malaysia (Teoh et al., 1985). Similar impacts were reported in Fiji where approximately, Aus$31/ha and Aus$21/ha was spent controlling M. micrantha in root crop and S. officinarum areas respectively (Macanawai et al., 2012b). In extreme cases, small blocks in Samoa have been abandoned, after being smothered by M. micrantha (ISSG, 2005).

For further information on economic impacts caused by M. micrantha, see Day et al. (2016) and Ellison et al. (2017).

Impact: Environmental

Once established, M. micrantha can have a major impact on natural ecosystems, in particular forest communities. This species can smother native vegetation, eventually killing many plants including trees, and decreasing biodiversity. M. micrantha also produces allelochemicals which have been shown to inhibit the germination of a number of agricultural seeds (Day et al., 2016).

In southern China, M. micrantha is considered to be a major threat to the local biodiversity (Xie, 2001; Zhang et al., 2004). M. micrantha was first observed on Neilingding Island (Guangdong Province, China) in 1997, and within 2 years, it covered 40-60% of the total land, decreasing biodiversity and altering habitats. The island is famous for its large population of Rhesus macaques, Macaca mulatta which are now under threat in this area (Xie, 2001).

In Chitwan National Park in Nepal, the greater one-horned rhinoceros (Rhinoceros unicorni) is also under threat, as M. micrantha is outcompeting plant species on which it browses (Sapkota, 2007; Murphy et al., 2013; Ellison et al., 2017).

Elsewhere in Nepal, it can be the dominant groundcover species, smothering other vegetation and preventing the emergence of seedlings of native and more desirable species such as Dalbergia sissoo and Shorea robusta. The presence of M. micrantha in Koshi Tappu Wildlife Reserve is affecting both flora and fauna, decreasing preferential habitat for many animal species and thus the overall biodiversity of the reserve (Baral and Adhikari, 2017).

Threatened Species

Threatened Species	Where Threatened	Mechanism	References
Eua zebrina (tutuila tree snail)	American Samoa	Ecosystem change / habitat alteration	US Fish and Wildlife Service (2014a)
Macaca mulatta (rhesus macaque)	China	Competition - monopolizing resources;Competition - smothering	Xie (2001)
Ostodes strigatus (sisi snail)	American Samoa	Ecosystem change / habitat alteration	US Fish and Wildlife Service (2014b)
Rhinoceros unicornis	Nepal	Competition - monopolizing resources;Rapid growth	Sapkota (2007), Murphy et al. (2013)

Social Impact

Forests in Nepal are a vital resource for many communities. They are a source of timber and medicinal plants and have been significantly impacted by M. micrantha (Baral and Adhikari, 2017). For example, Pogostemon benghalensis, which is used for oil extraction and is used as a stimulant, has declined due to M. micrantha.

In addition, Shorea robusta and several Dalbergia spp. are useful timber species for furniture, musical instruments and boat keels in Nepal and are now in decline from the impacts of M. micrantha. Timber from the forests is also used in temples. Dalbergia spp. provide fodder and fuelwood, as well as having pesticidal and medicinal properties. These species are also used in Hindu and Bhuddist rituals (Baral and Adhikari, 2017).

Risk and Impact Factors

Invasiveness

Proved invasive outside its native range

Has a broad native range

Highly adaptable to different environments

Is a habitat generalist

Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc

Pioneering in disturbed areas

Tolerant of shade

Highly mobile locally

Long lived

Fast growing

Has high reproductive potential

Has propagules that can remain viable for more than one year

Reproduces asexually

Impact outcomes

Conflict

Damaged ecosystem services

Ecosystem change/ habitat alteration

Infrastructure damage

Modification of nutrient regime

Modification of successional patterns

Monoculture formation

Negatively impacts agriculture

Negatively impacts cultural/traditional practices

Negatively impacts forestry

Negatively impacts animal health

Negatively impacts livelihoods

Reduced amenity values

Reduced native biodiversity

Threat to/ loss of endangered species

Threat to/ loss of native species

Impact mechanisms

Allelopathic

Competition - monopolizing resources

Competition - shading

Competition - smothering

Competition - strangling

Competition (unspecified)

Herbivory/grazing/browsing

Rapid growth

Altered food web

Behaviour disruption

Ecosystem change/ habitat alteration

Likelihood of entry/control

Highly likely to be transported internationally accidentally

Difficult to identify/detect as a commodity contaminant

Difficult/costly to control

Uses

In India, Malaysia and Taiwan, M. micrantha was introduced or has been used as a cover crop, for soil improvement or to prevent soil erosion. Studies in Bangladesh, show that M. micrantha can be used to control or suppress several Cyperus species (Ullah et al., 2016). However, given its weedy properties and how hard M. micrantha is to control itself, this may create problems later on, if M. micrantha infestations become too large and cannot be easily controlled. M. micrantha has also been used as fodder for sheep, goats and cattle in India, Malaysia, Nepal and Fiji (Wirjahardja, 1976; Zhang et al., 2004; Puzari et al., 2010; Macanawai et al., 2012b; Tripathi et al., 2012; PIER, 2015; Baral and Adhikari, 2017). However, it was also shown to cause hepatotoxicity when consumed (Sankaran, 2007; PIER, 2015).

Mikania micrantha has been reported to increase the growth and yield of rice in India when used as green manure (Abraham and Abraham, 2006; Sankaran, 2007; PIER, 2015). However, it is not particularly suitable for mulching and composting due to its high water content and rapid rate of decomposition (Sankaran, 2007).

Mikania micrantha has also been used as a medicinal herb in various countries as the plant is known to have anti-bacterial and anti-microbial properties. In India, the gum of the leaves is used by some tribal people for treating snake, insect and scorpion bites. In Fiji, Samoa and, to a lesser extent, Papua New Guinea, M. micrantha is used as a medicinal plant to treat cuts and nausea (Day et al., 2012a; 2016; Macanawai et al., 2012b). The leaves can be used as a topical ointment for eliminating discomfort of hornet, bee and ant stings (Parham, 1958; Sankaran, 2007; PIER, 2015). In Ecuador, it is reportedly used as a rat poison (Holmes, 1975).

Uses List

Environmental > Landscape improvement

Environmental > Soil conservation

Environmental > Soil improvement

Materials > Green manure

Materials > Mulches

Medicinal, pharmaceutical > Source of medicine/pharmaceutical

Medicinal, pharmaceutical > Traditional/folklore

Animal feed, fodder, forage > Forage

Detection and Inspection

The detection of M. micrantha should be the same for any other plant pest. This is particularly so for imports of machinery and goods into countries where M. micrantha is not already reported.

Prevention and Control

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Prevention

Good border and pre-border surveillance will help reduce the possibility of M. micrantha being accidentally introduced into a country. Such systems are particularly important if imported goods are coming from countries where M. micrantha is a major weed.

If the weed does establish in a country, then early detection and rapid eradication should be employed to minimize the chance of the weed spreading to other areas.

Control

Due to the rapid growth of M. micrantha and its substantial impacts to agriculture and the environment, much has been published on effective strategies to try to manage the weed. Methods are dependent on the habitat and land use in which M. micrantha has invaded. Clements et al. (2019) provides details on site-specific methods of controlling M. micrantha while Bora et al. (2023) provides a review of herbicide control.

Cultural Control

In Malaysia, it was found that the use of dorset horn sheep to graze infestations of M. micrantha and several other weeds resulted in cost savings of 15-25% for the overall weed control programme in Hevea brasiliensis (rubber) plantations (Arope et al., 1985).

In China, it is suggested that the establishment of a herb layer in managed orchards, forests, perennial crops (tea and tree plantations), parks and on newly developed areas should somewhat hinder M. micrantha seed germination, and by increasing understorey shade in forests, it should make growing conditions unsuitable for the vine (Zhang et al., 2004).

There have been numerous studies investigating whether other plant species could be used to control or suppress M. micrantha. In some parts of Asia, field dodder or Cuscuta campestris, a parasitic plant has been used to control M. micrantha. However, this species is also considered a pest of over 25 other species so its use is limited (Yuncker, 1932; Parker, 1972; Dawson et al., 1994; Lian et al., 2006).

Much work has been conducted on the use of sweet potato, Ipomoea batatas to suppress M. micrantha in China. In various trials, I. batatas has been able to suppress the growth of M. micrantha (Shen et al., 2016). Other plant species such as Delonix regia have also been tried as a means to suppress M. micrantha. Aqueous extracts of D. regia leaves have provided some mortality in potted seedlings (Kuo, 2003). Studies have also shown that grasses can be used to suppress growth and re-invasion of M. micrantha and it is possible to use tall grass species to outcompete M. micrantha (Zhou et al., 2016; 2022). There has also been some success in controlling or suppressing M. micrantha by community restructuring, using fast growing trees that can quickly form a canopy. Tree species such as Macaranga tanarius and Heteropanax fragans were deemed the most promising species (Han et al., 2017).

However, all these methods have limited uses in a practical sense. For instance, using I. batatas may be more effective where M. micrantha occurs as groundcover or in isolated patches. It does not appear to be very practical where M. micrantha grows into canopies or where M. micrantha is already well established. Similarly, the use of grasses has a limited use and would not be suitable in vegetable gardens or natural ecosystems. In these situations, other control methods are required to reduce populations of M. micrantha.

Mechanical Control

Manual and mechanical control is probably the main method to control M. micrantha in many countries in Asia and the Pacific (Clements et al., 2019). This is partly because M. micrantha affects agricultural systems, many of which are small block subsistence farmers who cannot afford expensive chemicals (Day et al., 2016; Clements et al., 2019). Hand-pulling M. micrantha is often used in vegetable gardens and around trees in small plantations, as there is less damage to other plants.

Slashing using bush knives is commonly used in the Pacific to clear land to make vegetable gardens or remove M. micrantha around trees in plantations. However, both hand-pulling and slashing are very labour-intensive and not sustainable due to the rapid growth of M. micrantha. In addition, slashing can also result in damage to desirable species and is not feasible for when M. micrantha is growing in the canopy (Zhang et al., 2004; Clements et al., 2019). Slashing is also inefficient as plants can readily regrow from broken stems if left lying on the ground and not burnt or buried (Holm et al., 1991; Day et al., 2016; Clements et al., 2019).

Studies in China and Fiji, found that regeneration of M. micrantha fragments, as a result of slashing can be significantly reduced if stem fragments are buried to a depth of 8 cm (Li et al., 2013; Macanawai et al., 2015). It is recommended that if slashing is used as the primary method of M. micrantha control, then care should be taken to minimize the possibility of regeneration by cutting fragments into smaller pieces, which reduces survival, burying the cut stems or raking the cut material into piles and burning (Li et al., 2013; Huang et al., 2015; Macanawai et al., 2015; Clements et al., 2019).

In Fiji, taro farms which utilized machinery to plough fields to control M. micrantha prior to sowing, had lower densities of M. micrantha than farms where hand-pulling and slashing were practiced. This is because M. micrantha plants are usually destroyed and/or buried, whereas manually slashed plants are usually left on ground where they can reshoot (Macanawai et al., 2010).

Ismail (2001) reported that traditionally, manual control of newly infested crop areas has been conducted by rolling, drying and burning the plants but this proved to be unsustainable. In India, manual methods (sickle weeding or uprooting) have been used but these are more expensive than chemical options (Sankaran, 1999).

When the vines of M. micrantha are cut near to the ground once a month for 3 consecutive months in summer and autumn and then in winter and spring, 90% of the plants can be eliminated. Hand-pulling in southern China is most effective before the end of October, i.e. prior to seed maturity, or during the March rainy season. A hand-pulling campaign by thousands of citizens was initiated by the Shenzhen Government (Guangdong Province) in 2000 and proved quite effective, as many dying trees damaged by M. micrantha subsequently recovered (Zhang et al., 2004).

Overall, manual control is more effective when M. micrantha populations or infestations are small and isolated. It is not a very effective control method when infestations are large and/or in natural settings.

Chemical Control

Young M. micrantha is susceptible to standard post-emergence herbicides such as 2,4-D, paraquat and glyphosate and these are the basis for chemical control in most plantation crops. In Asia, M. micrantha is particularly associated with rubber (Hevea brasiliensis) and oil palm (Elaeis guineensis) plantations and weed competition was greatest in immature crops and declined as rubber and oil palm plants matured. Complete eradication of M. micrantha from immature oil palm is important to ensure normal growth of the trees.

In Malaysia, applying paraquat and/or 2,4-D amine was the preferred method of control in these plantations. A field trial compared the efficacy of three treatments (grazing by sheep, mechanical slashing and the use of glyphosate+picloram) for the control of M. micrantha (and several other weeds) in a two-year-old H. brasiliensis plantation. Two months after treatment, over 90% of the weeds had regrown in plots that had been grazed or slashed, compared to <10% weed regeneration in chemically treated plots (Ahmad-Faiz, 1992).

A commercial preparation of a mixture of glyphosate and dicamba was evaluated for several years for weed control in >one-year-old oil palms on two plantations in Malaysia. This treatment resulted in a 90% weed control by 30 days after application and 40% by 120 days. Comparable treatment with a mixture of paraquat + diuron produced 95% control by 7 days and 0% by 120 days (Teng and The, 1990).

In Indonesia, field experiments were conducted to determine the effectiveness of four herbicides to control M. micrantha in immature oil palm. In all cases, the initial application was followed by a second. The best control was observed on plots that received 2,4-D amine, 2,4-D-sodium and ioxynil, applied 6 weeks apart, hexazinone + diuron at 4 weeks apart and 2,4-D-sodium followed 6 weeks later by glyphosate (Mangoensoekarjo, 1978). In a similar study, picloram + 2,4-D gave the best control of M. micrantha while glyphosate gave only moderate control after 4 weeks. Regrowth of M. micrantha and phytotoxic symptoms on oil palm were not observed on any plots up to 6 weeks after treatment (Hutauruk et al., 1982).

Triclopyr + picloram showed the best results in control trials of the weed in Indian forest plantations (Sankaran, 1999). The use of herbicides in China has been reviewed by Zhang et al. (2004). However, Shen et al. (2013) suggested that the type of herbicide used, should be dependent on the habitat in which M. micrantha grows. For instance, soil applied herbicides such as atrazine and bensulphuron have greater selectivity and are more suited to M. micrantha growing in areas where sugarcane, orchards and rubber are grown. Glyphosate, which is less selective, could be used in non-farming arming areas or where vegetation is not so valued, while sulfometuron-methyl could be used where M. micrantha is invading forests.

For more information on chemical control options, see Bora et al. (2023).

Biological Control

Biological control of M. micrantha was first attempted in the late 1970s, with surveys conducted by CABI in Central and South America (Cock, 1982). Nine arthropod natural enemies were found, of which Liothrips mikaniae (Thysanoptera: Phlaeothripidae) was considered the most promising. L. mikaniae was found only in sunny exposed areas in Colombia, Costa Rica, Trinidad, Peru and Venezuela. During host specificity tests against 37 species, including 12 other species from the Asteraceae, development to the adult stage occurred on only M. micrantha (Cock, 1982). The thrips were subsequently released into the Solomon Islands (1988) and Malaysia (1990) but failed to establish in either country. The thrips were also sent to Papua New Guinea in 1989 but the insect died out before field releases were conducted (Cock et al., 2000).

A survey of pathogens on M. micrantha conducted by CABI in Brazil from 1988-1989 and 1996-1999 found 11 species, with the rust Puccinia spegazzinii de Toni (Pucciniaceae) thought to be the most promising as a biocontrol agent (Barreto and Evans, 1995; Evans and Ellison, 2005). P. spegazzinii was found in numerous countries and prioritized because it was observed infecting both old and young leaves and petioles, causing premature senescence (Barreto and Evans, 1995; Ellison et al., 2004). Strains of P. spegazzinii were collected from Argentina, Brazil, Costa Rica, Ecuador, Peru and Trinidad and tested against M. micrantha from numerous countries in the introduced range to determine the most virulent strain for each population of M. micrantha. For southeast India, the strain from Trinidad, was considered to be the most suitable (Ellison et al., 2004; Ellison et al., 2007), while for the Pacific, the strain from eastern Ecuador was the most damaging (Day et al., 2013a). Initial host-range testing of P. spegazzinii was conducted against 175 species, including 46 species from the family Asteraceae, in trials in the UK, India and China and found this species to be highly specific; pustules developed on only M. micrantha and to a lesser extent M. cordata. P. spegazzinii was released in India around Assam, in October 2005 and March 2006, and Kerala in August 2006 (Ellison et al., 2008) but it failed to establish at any site (Ellison and Day, 2011). In 2006, the rust was introduced into mainland China but also failed to establish (Fu et al., 2006). Following host specificity testing on additional species, it was also introduced into Taiwan in 2008, where it established at numerous sites (Ellison and Day, 2011).

In 2008, the strain from eastern Ecuador was imported into Fiji and Papua New Guinea, following additional host-range testing conducted by CABI, on 11 species important to the Pacific region. The rust established widely in both countries. Both glasshouse and field studies have shown that the rust can significantly reduce growth rates and reduce the percent cover of M. micrantha by about 50% (Day et al., 2013a, b).

The rust has also been introduced to, and has established in Vanuatu (2012) and the Cook Islands (2017). In both countries, populations of M. micrantha are reported to have decreased in most areas, where the rust has established. The rust has been reported in the Solomon Islands, where it established naturally (Winston et al., 2021). P. spegazzinii was introduced into Guam and Palau but failed to establish in either country. The rust has also been approved for release in Australia, but field releases have not yet commenced.

Studies in China have shown that P. spegazzinii can significantly reduce metabolites and plant growth hormones, as well as reduce various metabolic pathways that can weaken the plant, slow growth and reproductive output (Ren et al., 2023; Zhang et al., 2023). The studies found that M. micrantha infected with P. spegazzinii had destruction of chlorophyll structure which led to a decrease in net photosynthetic rate. Overall, infected plants had lower growth rates, which makes M. micrantha less competitive.

Overall, P. spegazzinii has been tested against 287 plant species and has proven to be host specific to M. micrantha (Day and Riding, 2019). Given that M. micrantha affects many countries and current control methods are inadequate and costly or not sustainable, biological control using the rust would be a long-term, sustainable and environmentally-friendly method to control the weed in many impacted countries (Day et al., 2016; Day and Winston, 2016; Clements et al., 2019).

More information on the biology, host specificity and impact of P. spegazzinii on M. micrantha can be found in Ellison et al. (2008) and Day et al. (2013).

The butterfly Actinote anteas (Lepidoptera: Nymphalidae) was released into Indonesia as part of a biological control programme on Chromolaena odorata (Asteraceae) but was also found to feed on M. micrantha in the field. The young instar caterpillars scrape the epidermis on both sides of the leaf but do not appear to attack the petiole. Instead, they bind several leaves together with silk threads to form a shelter that may contain thousands of caterpillars (Chenon et al., 2002). In Sumatra, this species has helped control M. micrantha in a number of lowland areas (Day, 2012).

In China, studies have been conducted on Mikania micrantha wilt virus (MMWV) and its effect on M. micrantha (Wang et al., 2015). M. micrantha plants infected with MMWV had reduced growth and produced significantly fewer florets and seeds/m². MMWV did not infect 15 plant species from 11 families tested. However, MMWV has been reported infecting numerous other plant species including some crops. Wang et al. (2015) propose that MMWV could be used as a biological control agent to help control M. micrantha but care should be taken not to use around susceptible species.

Gaps in Knowledge/Research Needs

There has been much work conducted on the biology, ecology and impacts of M. micrantha. There has also been a great deal of research into its management, using herbicides, manual, cultural and biological control methods. However, each of these methods has limitations, such as being inappropriate to the land use or habitat, and/or are time consuming, costly and unsustainable.

While there has been some research into using other species to control or suppress M. micrantha, the practical applications are limited or have not been considered. For instance, using tall grasses cannot be used in most situations where M. micrantha grows. As for most weed species, site-specific management strategies are required. Therefore, it would be useful if such studies included a component on how such techniques could be applied in actual situations where M. micrantha invades.

The rust P. spegazzinii appears very effective in some areas but not so effective in others. For hot, tropical atolls, temperatures rarely go below 21 degrees which is the ideal temperature for sporulation. Thus, limiting the effectiveness of P. spegazzinii. Elsewhere, in parts of India, humidity may be too low. Therefore, seeking other natural enemies from the native range may be worthwhile.

Links to Websites

Website	URL	Comment
GISD/IASPMR: Invasive Alien Species Pathway Management Resource and DAISIE European Invasive Alien Species Gateway	https://doi.org/10.5061/dryad.m93f6	Data source for updated system data added to species habitat list.
Global register of Introduced and Invasive species (GRIIS)	http://griis.org/	Data source for updated system data added to species habitat list.

References

Abraham, M., Abraham, C.T., 2005. Biology of mile - a minute weed (Mikania micrantha H.B.K.), an alien invasive weed in Kerala.Indian Journal of Weed Science, 37(1/2):153-154.

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