Rice [Oryza sativa] tungro disease transmitted by the green leafhopper: Its epidemiology and forecasting technology
1992
Suzuki, Y. (Directorate of Food Crop Protection, Jakarta (Indonesia)) | Astika, I.G.N. | Widrawan, I.K.R. | Gede, I.G.N. | Raga, I.N. | Soeroto
Epidemiological studies of rice tungro disease in paddy fields were conducted with a view to developing its forecasting technology in the rice areas asynchronously planted in Bali. Tungro infections in paddy fields reached the highest peak on average in 6 weeks after transplanting, when the first generation large nymphs of Nephotettix virescens were most abundant. About 95% of the variance of the cumulative infections at harvest was explained by an index of infective nymphal density at this stage. Practical control thresholds were established for the monitoring in 2 to 5 weeks after transplanting on the basis of percentage of diseased hills. Onset of tungro dissemination coincided with the beginning of the wet season. The areas which might by infected by tungro in the first half of the wet season could by predicted with the number of infected locationsin the second half of the dry season. The increase in tungro incidences war preceded by the population build-up of N. virescens. It was recognized that increasing migratory activities of the first generation adults accounted for the population build-up. Tungro outbreaks were triggered by the presence of severelyinfected paddy fields in the asynchronously transplanted areas. The results obtained indicate that the conditions for the severe outbreaks are: first tungro intensity in paddy fields under young rice plants is more than 4 times as largeas the economic control thresholds, and secondly, at the transplanting time, the mean infective vector index in migrant producing fields in the area is larger than 15/25 strokes/100 hills
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