Distribution and biological control of Chromolaena odorata - Invasive Plants: Ecological and Agricultural Aspects - page 198

Ecology

Chromolaena odorata was previously known as Eupatorium odoratum before
the genus Eupatorium was split by King and Robinson [20]. Genus
Eupatorium , before it was split up, contained 1,200 species and the genus
Chromolaena contains 129 species, all from South and Central America and
the West Indies [21]. Chromolaena is distributed from Cuba to northern
Argentina. Cruttwell McFadyen [21] has given a detailed account of its ecolo-
gy in the neotropics. In its native habitat, it poses no threat as a weed as it is
kept under check by the native vegetation and natural enemies [21].
Chromolaena is a perennial plant, forming scrambling thickets and grows to
a height of 3 m. In areas near the equator, it grows up to an elevation of
1,000 m and thrives well where the average rainfall is about 2,000 mm per
year. It flowers during November-December in the northern hemisphere and
June-July in the southern hemisphere. Seeds are produced prolifically on ach-
enes and dispersed by wind. Because of its allelopathic properties, it sup-
presses neighboring vegetation [22]. In addition, during the dry season, the
aerial stems dry up and readily burn, but the stubbles remain alive and grow
rapidly to cover the area in the succeeding rainy season. This aggressive invad-
er reduces biodiversity and it is known to replace some of the other invasive
species such as Lantana camara L. (Verbanaceae) and Imperata cylindrica
(L.) Beauv. (Poaceae).
In the invaded areas of the world, it has become a serious weed in planta-
tion crops such as oil palm, coconut, citrus, cashew, teak and rubber, disturbed
forests, pastures and natural reserves. Chromolaena is not a problem in annu-
al crops as frequent ploughing and other cultural operations keep this weed
under control. In the disturbed forests, quick establishment of chromolaena
prevents self-seeding of forest trees. The thickets also interfere in the free
movement of wildlife. Growth of chromolaena along the riverbanks in South
Africa threatens Nile crocodile breeding [23].

Physical and chemical control

A slash and burn method of control is practiced in subsistence agricultural
regions in Asia and Africa. Mechanical control is widely used in plantation
crops but it is labor intensive and requires repeated operations. Tools used vary
depending upon the size of the operation. In small-scale operations, hand tools
such as picks, hand hoes, shovels and mattocks are used; while in large-scale
clearing situations, motorized brush cutters and tractor drawn mowers are
being used [24]. Fire has been proven effective in controlling early establish-
ment of the South African biotype of chromolaena but the biotype in other
parts of the world is resistant to fire.
Herbicides such as trichlopyr, glyphosate, 2,4-D amine, 2, 4-D/ioxynil and
picloram/2, 4-D have proven effective in controlling chromolaena [24].