Ageratum conyzoides is an erect, herbaceous annual, 30 to 80 cm tall; stems are covered with fine white hairs, leaves are opposite, pubescent with long petioles and glandular trichomes (Ming 1999). It can gain height up to 2 m in the Shivalik hills (Dogra, 2008, in Dogra et al. 2009). The inflorescence contain 30 to 50 self-incompatible pink, white or violet flowers arranged as a corymb (Jhansi and Ramanujam 1987, Kaul and Neelangini 1989, Ramanujam and Kalpana 1992, Kleinschimidt 1993, in Ming 1999). The fruit is an achene with an aristate pappus and is easily dispersed by wind (Lorenzi 1982, Scheffer 1990, Kalia and Singh 1993, Lam et al. 1993, Paradkar et al. 1993, Waterhouse 1993, Kshatriya et al. 1994, in Ming 1999). Seeds are positively photoblastic, and viability is often lost within 12 months (Marlks and Nwachuku 1986, Ladeira et al. 1987, in Ming 1999). The optimum germination temperature ranges from 20 to 25°C (Sauerborn and Koch 1988, in Ming 1999). The species has great morphological variation, and appears highly adaptable to different ecological conditions.

Ageratum is derived from the Greek \"a geras\", meaning non-aging, referring to the longevity of the flowers and the whole plant (Ming 1999).

Annual plants appear to have two great advantages: they reproduce early, so they have the potential for very high intrinsic rate of increase, and they can survive adverse condition as dormant seeds in the soil (Crawley, 1997, in Hassan Undated). A. conyzoides has the potential to produce many seeds (94,772 seeds per plant) and to shed seeds over extended times (5 to 8 months), as well as its extraordinary physiological plasticity, has enhanced its persistence in arable fields (Ekeleme et al. 2005). Invasiveness is enhanced by its ability to emerge in abundance (1000 plants per meter squared) (Anonymous 2000, in Ekeleme et al. 2005).
One plant of A. conyzoides may produce up to 40 000 seeds, with up to half of seeds germinating (Holm et al. 1977, in PIER 2008).
A. conyzoides flowers from July to March in India (Batish 2008). For the plant of equal biomass (both white- and violet-flowered), Hassan (Undated) found that the white-flowered produce more flowers and attract more insect pollinators than violet ones.

Medicinal: Ageratum conyzoides is an annual herb with a long history of traditional medicinal uses in many countries in the world, especially in the tropical and subtropical regions. A wide range of chemical compounds including alkaloids, flavonoids, chromenes, benzofurans and terpenoids have been isolated from this species. Extracts and metabolites from this plant have been found to possess pharmacological and insecticidal activities (Okunade 2002). A. conyzoides is widely utilized in traditional medicine by various cultures worldwide, although applications vary by region. In Central Africa it is used to treat pneumonia, but the most common use is to cure wounds and burns (Durodola 1977, in Ming 1999). Traditional communities in India use this species as a bacteriocide, antidysenteric, and antilithic (Borthakur and Baruah 1987, in Ming 1999), and in Asia, South America, and Africa, aqueous extract of this plant is used as a bacteriocide (Almagboul 1985, Ekundayo et al. 1988, in Ming 1999).
A crude material isolated from the leaves of A. conyzoides, a herb widely used by traditional medicine men for wound healing, is shown to exhibit antibacterial activity against Staphylococcus aureus in vitro (Durodola 1977).
It has been found that ingesting A. conyzoides can cause liver lesions and tumors. The plant contains the pyrrolizidine alkaloids lycopsamine and echinatine.

Insecticidal: A. conyzoides has natural biocide activity that may have agricultural insecticidal use, as shown by several research investigations in different countries. The leaves of the plant reportedly have moth-repellent properties (Pereira in 1929, in Ming 1999). The plant's terpenic compounds, mainly precocenes, with their antijuvenile hormonal activity are probably responsible for the insecticide effects. The affect of A. conyzoides on insect larva is to arrest juvenile development; this effect has been seen in Musca domestica (fly) larvae, Chilo partellus (Lepidoptera, Pyralidae), a sorghum pest, mosquitoes (Culex quinquefasciatus, Aedes aegypti, and Anopheles stephensi)
Essential oil extracts from the leaves of A. conyzoides caused significant morality of the maize grain weevil, Sitophilus zeamais. Mortality increased with the concentration of essential oil and the duration of exposure (Bouda et al. 2001).

Herbicidal: A. conyzoides showed strong inhibition of Raphanus sativus (radish) germination and growth in a bioassay. The leaves exhibited a greater suppression than the stem and root. The leaves of A. conyzoides reduced about 70% of the growth of Echinochloa crus-galli var. formosensis and completely inhibited emergence of Monochoria vaginalis var. plantaginea) and Aeschynomene indica in calcareous soil condition. Application of A. conyzoides leaves caused about 75% paddy weed reduction and increased yield by 14% compared with a herbicide treatment. Three phenolic compounds were identified in the leaves, stem and root including gallic acid, coumalic acid, and protocatechuic acid, and catechin was found only in the stem. P-hydroxybenzoic acid was detected in both A. conyzoides leaves and stem. Three additional putative allelochemicals were found in the leaves consisting of p-coumaric acid, sinapic acid, and benzoic acid. A. conyzoides might be a natural herbicide for weed control in paddy fields to reduce the dependence on synthetic herbicides (Xuan et al. 2004).

Ageratum conyzoides is a herb present in many tropical and subtropical environments. It is a weed of disturbed land in the Pacific island habitats including crops, pastures, plantations, waste land and roadsides (Swarbrick 1997, in PIER 2008). It is also found in clearings, grasslands, forests and along trails (Smith 1991, in PIER 2008).
A. conyzoides grows as a monoculture in grasslands, forests, agricultural, plantations and horticultural fields in India.
A. conyzoides thrives best in rich, moist, mineral soils with high humidity and tolerates shading. It is not tolerant to soils with poor fertility and therefore is only a minor weed on island atolls such as Niue. Hassan (Undated) observed that A. conyzoides in the Amani forest, Madagascar, is not found under the canopy but only in areas with light. This seems to suggest that the reproduction and distribution of this species is associated with light intensity. The study showed that the density of A. conyzoides was higher in open than in the semi-shaded areas.
One study, conducted in the north tropical and south subtropical mountainous zones in the Yunnan Province of China, found that the density of A. conyzoides was correlated with the distance of the plant from the road and that its maximum abundance occurred within 4 meters of the road. This supports the model of alien plants invading native plant communities in this part of China from primary colonisation points along road margins (Zhao et al. 2008).
A. conyzoides may grow from sea level to at least 2400 meters in altitude (Singh Undated). It is present from sea level to at least 1300 meters in Hawaii (Wagner et al. 1999, in PIER 2008) and in Himachal Pradesh the weed is established up to 1800 meters (Dogra et al. 2009).

Agricultural: Ageratum conyzoides is a weed in many annual and perennial crops and has been reported as host of many crop diseases (Ekeleme et al. 2005). Weeds interfere with growth and production of crops and therefore exert significant ecological and economic impacts (Singh et al. 2001, Batish et al. 2009). For example, in Asia rice yield Asia has been negatively associated with A. conyzoides density (Roder et al. 1998). Some studies have demonstrated allelopathy in the weed, however, shoot competition for light appears to be a major mode of interference in crops (Ekeleme et al. 2005).
Allelopathy: Allelopathy is a type of biotic interference wherein a plant releases bioactive metabolites into the surrounding environment. Growth of nearby vegetation is negatively affected and a selective advantage to the donor plant is provided (Batish et al. 2009a). Volatile components of A. conyzoides that contribute to phytoinhibition/allelopathy include precocenes and their derivatives monoterpenes and sesquiterpenes. There is much evidence that A. conyzoides inhibits germination and growth of other plants through chemicals produced by its root and shoot systems. Fresh leaves and volatile oils of A. conyzoides inhibit seedling growth of various crops (Kong et al. 1999) including peanut, redroot amaranth, cucumber and ryegrass (Kong Hu & Xu 2002). Studies have shown that shoot extracts of A. conyzoides inhibit germination of Amaranthus caudatus, Digitaria sanguinalis and lettuce (Lactuca sativa). Extracts of A. conyzoides inhibit germination of wheat and rice (Oryza sativa) seeds (Jha & Dhakal 1990, in Ming 1999). The phenolics present in leaf extracts and residues of A. conyzoides negatively interfere with the growth and development of wheat (Singh et al. 2003, in Batish et al. 2009a). Root and shoot length and biomass accumulation of rice are significantly reduced by 18 to 30% when grown in the rhizosphere soil of A. conyzoides (Batish et al. 2009a). Leaf debris of A. conyzoides deleteriously affects the early growth of rice (Batish et al. 2009b). Lastly, A. conyzoides causes reduction in chickpea (Cicer arietinum) growth and nodulation and (Batish et al. 2004). Phytoinhibition/allelopathy increases when plants are grown in nutrient-deficient conditions and decreases under fungal infection or aphid feeding (Kong Hu & Xu 2002).
Plant pathogen transmission: Kashina, Mabagala and Mpunami (2003) found that A. conyzoides is a weed host and disease reservoir of the Tomato yellow leaf curl Tanzania virus near tomato farms in Tanzania (Kashina, Mabagala & Mpunami 2003). A. conyzoides is a potentially important TYLCTZV reservoir because it occurs in abundant num¬bers within the tomato farms, it is associated with whitefly vectors, and it is found naturally infected with the virus. Elsewhere, A. conyzoides has been identified as host of Ageratum yellow vein virus.
Human health: A. conyzoides causes allergic reactions in some humans (Negi & Hajra 2007) and may pose a hazard to human health (Kohli & Batish 1996).\r\n
Case Study: Himalayan plant communities: The Shivilak Ranges form part of the North Indian Himalayas, well known for their rich floral diversity. However, A. conyzoides is poses a threat to the structure of natural plant grassland and forest communities and the dynamics of natural ecosystem processes (Singh et al. Undated A; Dogra et al. 2009). The weed replaces native grasses and medicinally important herbs and studies suggest it lowers biomass, biodiversity and creates homogenous monospecific stands (Dogra et al. 2009). It also negatively interferes with crop plants (wheat, chickpea, rice, maize, and sugarcane).

Integrated management: Experts recommend that future work on invasive plant species in the Shiwaliks in the Himalayas take an IPM approach. The problems associated with invasive species are aggravated due to lack of awareness, insufficient information on the species and its dimensions of the spread (Dogra, Kohli & Sood 2009). Batish (2008) recommends the compiling of comprehensive information on the invasive plant species, determining their possible modes of entry, understanding the biological and ecological attributes of the invasive plants, determining the socio-economic and ecological impact of the invasive plants in the area and disseminating this information to the general public and devising preventive measures for areas free of invasive weeds.

Chemical: Pre-emergence application of simazine, atrazine, diuron, oxadiazon, oxyfluorfen, methazole or metribuzin provides excellent control of this weed. Post-emergence application of 2.4-D controls established infestations (Rao 2000).
On the other hand eco-based, environment-friendly strategies for the effective control of A. conyzoides are suggested. Plant extracts of parthenin and eucalyptus (volatile essential oils) may hold promise in controlling A. conyzoides (Batish et al. 1997, Singh et al. 2002, in Batish et al. 2004) and some success has already been achieved using these and other natural plant extracts. For example, a study on the allelopathic effect of two volatile monoterpenes (cineole and citronellol) on A. conyzoides has revealed their potential for future weed management. Both the monoterpenes severely affected the germination, speed of germination, seedling growth, chlorophyll content and respiratory activity of A. conyzoides and after two weeks of exposure, the weed plants wilted. Cineole was the more toxic of the two monoterpenes (Singh Batish and Ravinder 2002).
The addition of activated charcoal, an inert material with high affinity for organic biomolecules, partly ameliorates the negative effects of A. conyzoides phenolic allelopathic root residues on rice (Oryza sativa) growth (Batish et al. 2009).

Field and crop management: Increased fallow length in slash-and-burn rice (Oryza sativa L.) production systems of northern Laos decreases weed pressure (Roder et al. 1998). Compared with continuous rice treatments treatments with fallow or cowpea (Vigna unguiculata) in the previous year had 32% less herbaceous weed biomass and 90% fewer A. conyzoides.
The timing of weed seedling emergence relative to the crop is important in planning and optimizing the time of weed control. Ekeleme and colleagues (2005) have predicted seedling emergence of tropical weed species, specifically in low-input and small-scale farms. To control weeds adequately, especially with limited use of herbicides, farmers need to know the timing and extent of weed seedling emergence before and during the growing season. Knowledge of when weeds emerge is equally applicable and beneficial to all forms of weed-management technologies (see: Ekeleme et al. 2005).

Research: To respond effectively to invasive species problems quantitative measurements of the impact of invasion on biodiversity are required (Schooler et al. 2006, in Dogra et al. 2009).