Ageratum conyzoides L.

Brazil: The optimum temperature for germination is between 25° and 30°C. The cycle from germination to fruiting lasts 60 to 80 days. In the state of Sao Paulo, Ageratum conyzoides can go through 3 complete cycles a year. Flowering is stimulated by short days. In periods of short days, some individuals can flower with only 2 pairs of leaves.
Northern Cameroon: Ageratum conyzoides has no photoperiodic requirement. It is capable of flowering and fruiting throughout the year if moisture is adequate. In areas of marked dry season, its development cycle is defined by the rainy season or by the height of the water table. In Rainfed cultures, germination begins with the first rains. After each soil working operation, new sprouts appear. This species can realize its full development cycle in less than two months and produce seeds that can germinate immediately at the end of the crop cycle. It naturally decays after about five months.
China : Ageratum conyzoides flowers and fruits all year round.
Côte d'Ivoire: In the cotton area, germination of Ageratum conyzoides takes place from June to November.
Mayotte: A. conyzoides flowers and fruits all the year round. It develops more during the dry season.
New Caledonia: Seeds remain viable 1 year and germination takes place from the beginning to the end of the rainy season. Flowering therefore ranges from the end of the rainy season and throughout the cool season. Fruiting occurs in the dry season before the plant dies.
Nicaragua: Ageratum conyzoides flowers and fruits mainly from December to June.
West Indies: Ageratum conyzoides flowers and fruits all year round.

Ageratum conyzoides is an annual species. It multiplies only by seeds. The fruits are transported by wind and water. The seeds are able to germinate immediately after their release. One individual can produce 40,000 to 94,772 seeds. The seed bank is very important; there are up to 10 million seeds per hectare in infested pasture.

Ageratum conyzoides grows in wetlands in agricultural plots, abandoned land, pens, roadsides and all types of plantations, up to 3000 m altitude. Rice fields at high altitude.

Brazil: Ageratum conyzoides adapts to different ecological conditions and can grow in virtually all tropical and subtropical regions. It thrives in all types of soil, particularly slightly clayey and locally damp but drought-tolerant. It does not tolerate temperatures below 10°C and cannot grow in regions subject to frost.
Northern Cameroon: Ageratum conyzoides is very ubiquitous. It develops as ruderal on the roadsides and as weed of a very large number of annual and perennial crops. It does not have a soil preference, provided the humidity is sufficient. In the sub-Sahelian region, it becomes frequent and abundant in areas where the rainfall is greater than 1300 mm. It is occasionally found in drier areas, in shallow wetlands and in plots bordering the river, with a flush water table.
China: Ageratum conyzoides grows in valleys, forests, forest edges on slopes, riverbanks, meadows and field margins.
Comoros: The species is very common everywhere in the three islands and adapts to all environments. It is a ruderal species common in fallow and fallow land.
Côte d'Ivoire: Ageratum conyzoides is a very common species in open areas without excessive shade and a weed of all annual and perennial crops and pastures.
Madagascar: Common in rainfed crops in the Highlands and at average altitudes in terrace crops, at the bottom of slopes bordering lowland rice paddies or alluvial plains.
Mauritius : Very common weed and present in fallows and roadsides.
Mayotte: A. conyzoides is a very common species, mainly in the north of the island. It is naturalized in the anthropized and wet environments (cultures, roadsides, villages, forest openings).
New Caledonia: It is frequently found on roadsides, in wastelands and in certain pastures. It prefers wet and shady sites, aerated soils.
Nicaragua: Abundant weed in disturbed environments throughout the country; from 0 to 1200 m altitude.
Reunion: The species is very common everywhere in Reunion, including in pastures at altitude up to 1700 m. It develops as ruderal on the roadsides and as adventitious of a large number of annual and perennial crops. It does not have a preference for a particular soil, but it needs enough moisture and light to grow.
Seychelles: This species prefers moist habitats but can also grow in dry conditions.
South Africa: Crop weed, often near water. Weed escaping cultivation and post-cultivation, often pioneering on cleared land such as logging tracks, also in grassland and Acacia woodland.
West Indies: Ageratum conyzoides is a very common species in gardens, fallows and wasteland. It tolerates damp and shady areas. Rarely abundant in crops, it is often found in association with common nitrophilous species.

Host of pests and pathogens: Ageratum conyzoides is a host for a parasite (Cassytha filiformis L.) and for different crop diseases (Cercospora agerati Stevens, Puccinia conoclinii Seym.). It also hosts nematodes. Meloidogyne sp, M. incognita (Kofoid & White) Chitwood, M. javanica Treud, M. arenaria Chitwood, M. arenaria Chitwood M. thamensis Chitwood, Pratylenchus pratensis (Man) Philip, Rotylenchulus reniformis Linford & Oliveira , Aphelenchoides fragariae (Ritz.-Bos) Christie. It also hosts viruses such as tobacco mosaic virus and mosaic virus anemone. It also has allelopathic properties for other species (inhibition of germination and growth) by releasing a plant phytotoxin in the soil from residues of its leaves.

Service plant characteristics: Ageratum conyzoides harbours phytoseid mites such as Ambyseius newsami, which can regulate infestations of Panonychus citri, the yellow citrus mite. It also appears to reduce the incidence of attacks by Brevipalpus phoenicis and Phyllocoptruta oleivora in citrus orchards.

Origin

Agratum conyzoides is native to Central and South America.

Worldwide distribution

Pantropical to subtropical.

Global harmfulness
 
Ageratum conyzoides is an invasive plant of crops, pastures and a common ruderal species. Moreover, it also has allelopathic properties for other species (inhibition of germination and growth) by releasing a phytotoxin in the soil from residues of its leaves. The species is one of 300 major invasive species in tropical Australia, the Indian Ocean and Oceania.
 
Local harmfulness
 
Benin: A. conyzoides is a common species, but not abundant.
Brazil: Ageratum conizoides is mainly a weed of orchards, particularly citrus orchards.
Burkina Faso: A. conyzoides is a common species, but not abundant.
Chad: The species is rare and scarce.
Comoros: This is a weed frequent and abundant in vegetables but also present in other cultures.
Côte d'Ivoire: The species is common and usually abundant. In the cotton area, it is highly dominant in the areas of Béoumi, Bouaflé, Boundiali, Daloa, Dianra, Ferkéssédougou, Kani, Niofoin, Odienné, Sarhala, Tortiya and Zuénoula.
Ghana: The species is common and usually abundant.
Kenya: The species is common and scarce.
Madagascar: common species and locally very harmful to upland rice crops and vegetable crops.
Mali: The species is common and scarce.
Mayotte: Ageratum conyzoides is a weed present in 16% of crop fields, particularly in orchards and vegetable crops. It is also abundant in pineapple crops. It is very abundant in the north of the island.
Nigeria: The species is rare, but abundant when present.
New Caledonia: The species was observed in New Caledonia since the mid-19th century. It is now a weed of the most popular crops on the territory. This is not an invasive pasture as such, but its presence combined with other minor weed species constitute a community of little or no palatable species whose abundance is involved in the degradation of the pastures and in some cases seriously competitive production of forage species.
Uganda: The species is common and usually abundant.
Reunion: A. conyzoides is a common weed for a very large number of crops. It occurs in 60% of records with an average coverage rate of 7 to 15%. In sugar cane cultivation it is found in nearly all environments (Fr> 50%), with infestations of up to 50% coverage. The problem caused by this weed is minimal. In gardening and pineapple culture, it is very common (Fr> 50%) and generally abundant with many situation where coverage exceeds 30%, sometimes can reach up to 100%. For these cultures, A. conyzoides is found in the group of the most harmful species. This is explained by a lack of effectiveness of herbicides registered on these crops. In the lentils of Cilaos, is found in 30% of the records but it is not a major agronomic stress because it remains easy to weed.
Senegal: A. conyzoides is rare, but abundant when present.
Seychelles: A. conyzoides is an aggressive colonizer of cultivated areas, both on heavy and light soils. It is found in the annual crops between wide inter rows and in permanent crops, such as in gardening and orchard.
South Africa: Ageratum conyzoides competes with native species and may replace them.
Tanzania: The species is common and usually abundant.
West Indies: Ageratum conyzoides is a frequent but not very harmful weed. It is largely controlled by all weed control techniques. However, its abundance can be locally important in vegetable crops where tillage operations favour seed dissemination and germination. It can also be abundant in orchards where weed management is done only by chemical means.

Medicinal: Ageratum conyzoides is sometimes used as a medicinal plant against fever

Global control

Manual control: Ageratum conyzoides can be easily controlled manually or by hoeing at the seedling stage.
Chemical control: Seedlings and young individuals are easily removed by 2,4-D, MCPA or any other growth regulator normally used in cereal crops.

For advice on weeding annual broadleaf weeds of irrigated and lowland rice in Africa, see: http://portal.wiktrop.org/document/show/19

Local control

Côte d'Ivoire: In cotton crop, Ageratum conyzoides is not controlled by the pre-emergence herbicides popularized. Two active ingredients allow a good control of this weed (oxadiargyl and trifloxysulfuron). Similarly, post-emergence treatment of weeds and pre-emergence treatment of cotton and directed treatment with shield are effective means of control.
- Pre-emergence treatment of weeds and cotton: on clean soil, the day of sowing or the day after, apply with a backpack sprayer oxadiargyl at 240g a.i./ha
- Post emergence treatment of weeds and cotton: 15 to 21 days after sowing cotton, apply with a backpack sprayer trifloxysulfuron at 11g a.i./ha
- Post emergence treatment of weeds and pre-emergence of cotton: Sow cotton in a lightly weeded field. The day of sowing or the day after apply with a backpack sprayer an authorized systemic total herbicide (glyphosate at 1440 g a.i./ha or sulfosate at 1920 g a.i./ha) to which may or may not be associated a pre-emergence herbicide such as s-metolachlor + prometryn.
- Directed treatment with a shield: In post-emergence of weeds and cotton, apply with a backpack sprayer equipped with a shield and only in the row (without touching the cotton) an authorized systemic total herbicide such as glyphosate.
Madagascar: The manual control of A. conyzoides is very time consuming. Chemically, it is easily controlled with herbicicdes such as alachlor, atrazine, diuron or oxadiazon in pre-emergence or early post-emergence; 2,4-D or glyphosate on young or old plants. A. conyzoides is well controlled by mulching and disappears gradually in direct sowing on vegetation cover.
New Caledonia: In pasture, the germination and propagation of this annual species should be prevented as much as possible by maintaining a dense herbaceous cover. The insulated individuals can be easily torn off by hand. On settled stands, the rotary crushing alone causes the regrowth of the plant and can contribute to its dispersion if it is carried out with fruiting. It will be supplemented by a full spray herbicide treatment on extended stands with grass-selective active ingredients (2,4-D, triclopyr, or combining the 2 active ingredients).
Reunion: In sugar cane, it is easily controlled, with the herbicides of pre-emergence or post-emergence antidicotyledones approved.

 2014
 

Data acquired at Reunion on the effectiveness of herbicide products in the context of the sugar cane herbicide network by eRcane with funding from ODEADOM and ONEMA. Action led by the French Ministry in charge of agri-food and forest agriculture, with the financial support of the National Office for Water and Aquatic Environments, on credits from the levy for diffuse pollution attributed to the financing of the Ecophyto plan.
West Indies: Good management of Ageratum conyzoides requires alternating weed control techniques.

Herbarium pictures ReCOLNAT: https://explore.recolnat.org/search/botanique/simplequery=Ageratum%2520conyzoides