Family: Asteraceae

Common names: Whitetop, Whitehead, Barley flower, Congress Grass, Amargosa, Escoba Amarga

An erect annual herb with alternate, deeply-dissected leaves, growing up to 2 m tall with much branched inflorescences bearing white flower heads and numerous obovoid, smooth and black achenes.

Parthenium is a native of tropical America and was introduced into Africa, Asia and Oceania in cereal and grass seed shipments from U.S.A. during the 1950s.

Parthenium is wide-spread in grassland, fruit tree orchards and arable land in neutral and acid soils.

In Central America and the Caribbean area parthenium mainly thrives in areas repeatedly treated with paraquat or with certain soil-acting herbicides selectively used in vegetable and legume crops such as trifluralin, diphenamid and others.

The germination of parthenium reaches a maximum 1-6 months after the achenes ripen. The seeds are not able to germinate in soil below a depth of 5 cm. In the Caribbean area parthenium flowers 30-45 days after germination and the whole plant cycle is completed within about 5 months, with a single plant producing an average of 810 flower heads.

In infested crop areas deep ploughing during the land preparation can reduce the stand of parthenium weed. In small areas hand hoeing during the early growth stages prevents flowering. Hoeing mature plants is ineffective because of regrowth from crown buds. In India, in heavy infested areas, replacement of parthenium has been achieved through the use of plants of Cassia spp.. Such a practice consists in manual removal of parthenium plants and subsequent seeding of Cassia plants (C. sericea or C. uniflora Mill.), population size of which increased with time in relation to that of parthenium. Two years later Cassia:parthenium ratio was higher than 21:1.