Bidens alba

B. alba is an erect annual or short-lived perennial herb native to Florida, South America and the West Indies. It has been introduced to the Pacific region and is now naturalized on many islands. It is a major weed on the Marshall Islands (Englberger, 2009).

B. alba is common in disturbed areas, such as on road sides and in pastures. It is particularly abundant in open and sandy areas such as atolls. It does not grow well in shade or in the understory of forests (Englberger, 2009).

B. alba spreads by its barbed seeds, which adhere to clothing, feathers and fur. It can also be carried in soil and on machinery (Englberger, 2009).

Description

Taken from Englberger (2009):

This erect annual or short-lived perennial herb grows 0.3-1.5 m high. It can be distinguished by its opposite, simple or trifoliate leaves; heads of yellow disk florets, surrounded by 5-8 white ray florets; and black, straight achenes 3.8-12.7 cm long, bearing several needle-like barbs.

Prevention and Control

Taken from Englberger (2009):

Pulling is difficult, but hand weeding can be effective if done repeatedly for an extended period. For chemical control, triclopyr can be used as a foliar spray. Some Marshall Islanders recommend using seawater to control this weed.