Rice ragged stunt (RRS) disease was first observed in Thailand in 1978. The causal agent is a virus with polyhedral particles 60 nm in diameter which is transmitted by the brown planthopper, Nilaparvata lugens and N. bakeri in a persistent manner without transovarial passage. Wild rice (Oryza sp.) is the host plant affected by the disease.
The cultivation of the rice variety RD 7 in 1980 contributed to the remarkable spread of RRS disease. The damaged area covered 33,279 ha in the Central Plain of the country. After the release of the two new varieties RD 21 and RD 23 the disease occurrence was significantly reduced. Use of resistant varieties is one of the most practical methods of control of the disease.