Introduction

Ageratina adenophora (Sprengel) King and Robinson (=Eupatorium adenophorum, E. glandulosum, E. pasadense) (Asterales: Asteraceae) is popularly known as the Crofton weed; other common names are eupatory, sticky snakeroot, cat weed, hemp agrimony, sticky agrimony, Mexican devil, and sticky eupatorium in different parts of the world (Hoshovsky and Lichti, 2007). In Hawaii it is known as Maui pāmakani and pāmakani haole and in Nepal as banmara (killer of the forests). Usually, it grows into an erect herb (occasionally into a subshrub) of one to three meters in height, with trailing purplish to chocolate-brown branches that strike roots upon contact with soil, resulting in dense thickets (Bess and Haramoto, 1958). The base of the plant is woody and densely clothed with stalked glandular hairs. Leaves are dark green, opposite, deltoid-ovate, serrate, and purple underneath, and each grows to about 10 cm in length. Flowers are white and borne terminally in compound clusters in spring and summer. The seed is an achene, varying from elliptic to oblanceolate, often gibbous, 1.5–2 mm long, 0.3–0.5 mm wide; with five prominent ribs and five to 40 pappi with slender scabrous bristles (Hickman, 1993). Dispersal occurs by wind-borne seeds and each plant produces about 100,000 seeds per season. Seeds are also spread by water, as contaminants of agricultural produce, via sand and gravel used in road preparation, via soil sticking to animals, machinery, and vehicles, and by adhering to footwear or clothing of farm workers (Parsons, 1992).