Cyperus iria (rice flatsedge)

C. iria is rated by Holm et al. (1977) as one of the three most important weeds of rice in Sri Lanka, India and the Philippines. It is a principal weed in Indonesia and Japan and a common weed in Fiji, Thailand and the USA. It is principally a weed of rice around the world but Holm et al. (1977) also noted its occurrence in bananas, cassava, groundnuts, maize, pastures, pineapples, sweet potatoes, tea and vegetables. It is difficult to separate the competitive effects of C. iria from those of other components of the weed flora but the weed caused 40% yield reductions in rice (Ampong-Nyarko and DeDatta, 1991).

The costs of controlling C. iria, whether manual, mechanical or chemical, are significant. C. iria is a host for several pests of rice. In Cuba, it is a host of the rice nematodes Pratylenchus zeae and Hirschmanniella spinicaudata (Fernandez and Ortega, 1982). Criconemella onoensis is a rice nematode which uses C. iria as a host in the southern USA. Complete control of the weed is necessary before nematicides (e.g. fensulfothion) can be effective in increasing rice yields (Hollis, 1972).

Arthropod rice pests which use C. iria as a host plant include Scotinophara latiuscula (Barrion and Litsinger, 1987), Nisia atrovenosa (Cruz and Dela-Cruz, 1986), Lissorhoptrus brevirostris (Meneses-Carbonell and Carbonell, 1985), Nymphula depunctalis (Pillai and Nair, 1979), Baliothrips biformis and B. holorphnus (Ananthakrishnan and Kandasamy, 1977).

Pathogens of rice that have been reported on C. iria include Pyricularia oryzae [Magnaporthe grisea] (Singh and Singh, 1988), Rhizoctonia solani (Gokulapalan and Nair, 1983) and Acrocylindrium oryzae [Sarocladium oryzae] (Balakrishnan and Nair, 1981). Also the nematode Pratylenchus zeae (Waterhouse, 1994).