Crofton weed, Ageratina adenophora (Sprengel) R. King and H. Robinson, originally from Central America, was introduced into China in the 1940s. The weed spreads rapidly and is seriously damaging grasslands and hindering livestock production in southwestern China. To tackle the weed problem and allow the sustainable use of pastures, an integrated strategy, based on biological control and habitat restoration, is being explored. In 1983, a gall fly Procecidochares utilis Stone, originating from Mexico, was introduced from Tibet into Yunnan Province for the control of crofton weed. The current efficacy of this agent was investigated, but no significant control effect was found due to more than 60% parasitism by native parasitoids. Surveys were undertaken to identify any indigenous fungal pathogens infecting the weed. At least six strains of Alternaria alternata (Fr.) Keissler and a Pestalotiopsis sp. were isolated from leaves. One strain of Alt. alternata was selected for further study as a prospective mycoherbicide. Field trials on ecological restoration using competitive native plants and forages showed that A. adenophora was less interspecifically competitive than Setaria sphacelata (Schum.) Stapf. ex Massey cv. Narok.