Rice Ragged Stunt and Rice Grassy Stunt: Farmer's Disaster from the Brown Planthopper

Abstract

Ragged stunt and grassy stunt are important diseases of rice which are caused by rice ragged stunt virus (RRSV) and rice grassy stunt virus (RGSV). Both viruses have the brown planthopper (BPH) as insect vector. Symptoms of RRSV infected rice plants consisted of stunting and appearance of twisted leaves, ragged leaves, and swelling along the leaf vein. Panicle exsertion is delayed and incomplete. Whereas, symptoms of RGSV infected rice plants consisted of stunting, excessive tiller, narrow and yellowing leaf with yellow to brown spots, panicles are not produced or produce incomplete panicles. Symptoms and disease severity are usually depend on the virus types, variety and virus transmitted growth stage of rice. Controlling methods normally are elimination of virus sources, planting resistant rice varieties to BPH and frequently investigate insect vectors and diseased rice plants. Moreover, insecticide application is also recommended when infected rice plant and 1 BPH /plant/hill are found. During December 2009 to January 2010, there was a severe outbreak of RRS and RGS in Central and lower Northern region of Thailand. At this serious situation, controlling strategies has been assigned to achieve the high and fast efficacy in controlling. Hence, plough was recommended for rice at seedling to tillering stage. If 10% of infected plants was found at tillering to panicle stage, remove the infected plants and burning or burying were suggested. Insect controlling and plough after harvested were done at booting and harvesting stage. In order to interrupt BPH, RRSV and RGSV life cycle, stop planting in those areas at least one month. Moreover, recommended rice varieties of Rice Department should be employed for the next crop to prevent BPH destroying and infected of RRSV and RGSV.