Integrated management of rice tungro disease in South Sulawesi, Indonesia

Abstract

Tungro virus disease of rice has been a serious problem in rice production in South Sulawesi, Indonesia. During 1977–1981, the annual population fluctuation pattern of the vectors Nephotettix virescens and N. nigropictus estimated by light trapping peaked at the end of the wet and the dry crop seasons. Average tungro incidence in monthly planted fields was higher in plots planted in the months when vector catches were greater. To solve tungro problems, an integrated management scheme was developed in 1983. The scheme had four components: (1) planting of two rice crops in those months in which the vector population is low; (2) scheduled planting to have nearly synchronous growth in each area; (3) rotation of cultivars with different degrees of resistance to N. virescens; (4) application of insecticide to reduce vector density in tungro-affected fields. Since 1983, tungro incidence has been generally low and the use of insecticide has been drastically reduced in those areas in which the integrated management scheme was adopted. To assess the relative importance of the practices for tungro management, tungro epidemiology was studied at Sidrap and Maros, South Sulawesi. Surveys in 1985 and 1986 at Sidrap revealed that 90% of rice fields were planted following the recommended planting schedule and therefore a definite fallow period was obtained for one or more months between the dry and wet crop seasons in each area. During this period in Sidrap, an average of 78–85% of rice growers planted recommended cultivars. At Maros, peak periods in the annual green leafhopper (GLH) population fluctuation pattern in 1985–1987 appeared 1 month ahead of those in the pattern obtained during 1977–1981. The shift was probably associated with a shift of 1 month in the crop establishment for dry and wet seasons. In the 1987–1988 dry season in Sidrap, where cropping was scheduled for planting in November, four rice cultivars were planted in the first week of October, November, December, January and February, and development of the vectors and tungro were compared. Vector density was low in the October planting; it increased slowly after transplanting in the November planting, and it increased rapidly and reached high levels in the December and later plantings. The average tungro incidence at 56 days after transplanting was negligible or zero in the October, November and December plantings, but it was 20% in the January planting and as high as 60% in the February planting. In the January and February plantings, tungro incidence was also high in cultivars recommended for that dry season in the area. In the similar trial in the same season at Maros, with wet weather, the tungro incidence was negligible or zero in all plantings but the vector density was high in the February and March plantings. These results indicate that the vector source was limited and the tungro source was scanty in the two locations at the time when planting was scheduled. Tungro infection could occur, but only at the maturing stage or when planting was delayed. Low tungro incidence under the management scheme was mainly because of slow rate of vector population increase and absence or scarcity of tungro source in the area. With regard to the component practices involved, the deployment of cultivar rotation appeared to have a limited role in reducing tungro incidence. Scheduled uniform planting may be of key importance.