This paper was presented at the Symposium in Weed Science held on 10-12 Apr. 1984 at Bogor, Indonesia. The problems associated with M. pigra, its distribution and methods used for its control in Thailand are discussed. M. pigra has been classified as a noxious weed in Thailand since 1974. When growing along water systems it obstructs and diverts water flow causing excessive sedimentation. Over 10 000 ha of land, mostly adjacent to water, are estimated to be infested. Integrated control by cutting, burning and allowing the cut stumps to regrow followed by herbicide application is a safe, effective and economical control method. Fosamine, glyphosate, bromacil and dicamba may be used for its control, but only fosamine and glyphosate have been used for large-scale control by aerial spraying.
