Perennial herb, up to 2m, aromatic, with white or flashy pink flowers.
Scientific name: Ageratina adenophora (Spreng.) R. M. King & H. Rob.
Common names: croftonweed, sticky snakeroot, Mexican devil, catweed, eupatory
Family: Asteraceae (Compositae)
Status in Portugal: invasive species (listed in the Decreto-Lei nº 92/2019, 10 july)
Risk Assessment score: 28 | Value obtained according to a protocol adapted from the Australian Weed Risk Assessment (Pheloung et al. 1999), by Morais et al. (2017), according to which values above 13 mean that the species has risk of having invasive behavior in the Portuguese territory | Updated on 30/09/2017.
Synonymy: Ageratina trapezoidea (Kunth) R. M. King & H. Rob., Eupatorium adenophorum Spreng., Eupatorium glandulosum Kunth, non Michx., Eupatorium pasdadense Parish, Eupatorium trapezoideum Kunth
Last update: 08/07/2021
How to recognise it
Perennial herb or subshrub up to 2 m, with ramified stems, purple when young, densely glandular–pubescent.
Leaves: opposite, triangular to rhomboid, with 4-10 x 2-9 cm, acuminate, with a lengthy petiole, serrate on the margin, densely pubescent, dark green on the upper surface and violet on the lower surface.
Flowers: white, sometimes pink or purple, arranged in dense capitula (10 to 60 flowers) of 5-10 mm diameter, with a campanulate involucre, tubular, with 5 lobes.
Fruits: black cypselas, glabrous, and 2 mm long, with a 3-4 mm white pappus.
Flowering: March to July.
There are other Ageratina species with white flowers with which Ageratina adenophora may be confused with. Ageratina riparia (Regel) R. King & H. Robinson has some similarity but is smaller (up to 30 cm in height) and the leaves are narrower. Ageratina ligustrina (DC.) R. M. King & H. Robinson, is also similar but the upper surface of the leaves is shiny dark green.
Characteristics that aid invasion
It propagates by seed, producing a high number of seeds (each plant may produce up to 60000 seeds/m2) which are easily dispersed by wind, water and animals.
Native distribution area
Central America (Mexico).
Distribution in Portugal
Azores archipelago (islands of São Miguel, Terceira, S. Jorge, Pico, Faial), Madeira archipelago (islands of Madeira, Porto Santo and Desertas islands).
Geographic areas where there are records of Ageratina adenophora
Other places where the species is invasive
Europe (Spain, Italy, France, Greece) Australia, New Zealand, western USA (California), Central America (Jamaica), Asia (China, India), Africa (South Africa, Nigeria, Kenya).
Probably accidental. It’s probable that it has also been used as ornamental.
Preferential invasion environments
Cliffs, banks of watercourses and roadsides, including agricultural and disturbed areas.
It also invades natural and semi-natural areas.
Impacts on ecossystems
The rapid growth leads to the formation of impenetrable dense areas that may inhibit the development of native vegetation.
Potentially high costs in applying control methodologies, mainly in cultivated areas.
It reduces productivity in crop fields.
All parts of the plant are very aromatic, being able to cause allergic reactions.
It is a very toxic plant for mammals, especially horses.
It has allelopathic effects.
Controlling an invasive species demands a well-planned management, which includes the determination of the invaded area, identifying the causes of invasion, assessing the impacts, defining the intervention priorities, selecting the adequate control methodologies and their application. Afterwards it is fundamental to monitor the efficiency of the methodologies and recuperation of the intervened area as to perform, whenever necessary, the follow-up control.
The control methodologies used for Ageratina adenophora include:
Hand pulling: preferential methodology for invaded areas of small dimensions. In compacted substrates, hand pulling should be made during the rainy as to facilitate the removal of the root system.
Cutting. It’s an alternative to hand pulling, mainly in extensive areas that are invaded by the species.
Whatever the methods being used, it should be guaranteed that the extracted plants do not remain in the affected location, since their dried parts are toxic to animals.
Physical + chemical control
Cut stump method. Cut the stems close to the ground as much as possible followed by application of herbicide (active substance: glyphosate, 2, 4-D) into the cut surface, when sprouting reaches 15 to 40 cm height.
Foliar application of herbicide. Herbicide spray (active substance: glyphosate, 2,4-D) limiting the exposure to the target species. It should be done when plant’s growth is at its maximum.
Procecidochares utilisStone (Diptera: Tephritidae) thas been used with some success in various locations (China, India, Nepal, Australia, New Zealand, South Africa) to control Ageratina adenophora. This species forms galls in the stems of Ageratina adenophora reducing the germination rate. It is supposed that gall-maker had been introduced in the Madeira island before 1971 to control Ageratina adenophora, although there are no concrete references to this.
The fungus Passalora ageratinae (=“Phaeoramularia” sp.) (Mycosphaerellales: Mycosphaerellaceae) has been used since 1987 in South Africa with moderate success in controlling Ageratina adenophora.
These agents have not yet been tested in Portugal as to verify their safety relatively to native species, so they use have not yet constituted an alternative in our country.
Visit the webpage How to Control for additional and more detailed information about the correct application of these methodologies.
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