| It has conspicuous advantage of yield enhancement to cultivate two-line hybrid rice. However, with the improvement of fertilization and alternation of varieties, rice false smut, Ustilaginoidea virens (Cke) Tak has become a main disease in two-line hybrid rice. Occurring severely, this disease not only causes rice yield loss, but also results in contaminated and bad-quality rice. So this disease has become a pending problem involved in wide extension of two-line hybrid rice. Its occurrence, infecting factors and integrated control tactic were studied. The disease epidemic was illustrated and the forecasting model of yield loss was established(1).The field observation showed that the pathogen invaded into floral organ at booting stage and light yellow blocks first appeared as spore balls with silver membranes at the cleft of lemma to wrap the lemma at flowering and heading stages. The spore balls, with expanding, changed from orange to dark green in color and finally breaks out, giving off dark green powders, i.e. chlamydospores. Epidemic peak period is from grouting to milky-stage, and the disease incidence tended stable at yellow-ripeness. On the two-line hybrid rice as second season, the earliest symptom was found in early September, spore balls increased in number in the middle September expands in size rapidly in the late September. The infection prevailed in the early October and tends to stable after the middle October. The epidemic dynamics fit to Logistic curve. The spatial pattern of the disease is aggregation distribution affected by environment factors(2). The statistical analysis showed that yield loss is correlated with disease indices, the rate of disease spikes and the number of disease grains per 100 spikes. Two models were built: Weber model: disease index (X), theoretical production value (Yi) Linear model: the rate of disease spike (XI), the number of disease grain per 100 spikes (X2), theoretical production value (Yi) The value by the model accords with the practical one through test.The influence factors on occurrence and control of false smut on two-line hybrid rice were examined. The disease resistance of two-line hybrid rice is the most important factor. High plantdensity, late or excessive nitrogen fertilization, and deficient Kalium supply were in favor of disease prevalence. Two-line hybrid rice still gave a high yield due to less disease when rice seedlings at age of 25-30d and with planting mode of wide-narrow row, were transplanted with density of 225 thousands of plants per ha before July 15th and when the paddyfields were initially fertilized with 187.5-225kg/ha nitrogen fertilizer, with the 1:0.8 ration of nitrogen to kalium 10d after transplantation, and when reasonable irrigation are applied.The investigation method of stage of this disease and economic threshold are ascertained. And chemical control technique is established.The paddies with disease indices, determined by the sampling of parallel line, beyond the economic threshold were sprayed with suitable fungicides at the end of booting stage. Susceptible varieties were continuously sprayed two times with an interval of 7-10d. The author selected an assortment of correlative fungicides with best control.The integrated management of rice false smut is suggested with good demonstration examples: cultivation of disease-resistant rice cultivars; sterilization of seeds and seedbed; two periods of seeding stage, planting mode of wide-narrow row; reasonable irrigation and fertilization and fungicide spray e in time based on an accurate monitoring and forecasting of this disease.A yield testing on the spot in October 1999 came into a conclusion that the integrated management effectively controlled this disease to the level of economic threshold and gave obviously economic, social and ecological benefits.
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