1992 Volume 58 Issue 2 Pages 259-266
To construct a mechanistic model of the behavior of tricyclazole on rice leaves and its efficacy for the prevention of leaf blast epidemics under field conditions, quantitative data of temporal changes of the amount of fungicide residues on rice leave at various positions and a concentration-response curve of protectant effect against blast fungus versus fungicide concentration were determined. Disease progression in the filed with or without application of the fungicide was assessed to evaluate feasibility of the data. Tricyclazole was applied in two different timing to a rice field. Temporal changes of tricyclazole residues on leaves obey a decay curve model. On the leaves that had fully developed at the time of application, estimates of initial deposits of the fungicide ranged from 4.39 to 19.69 μg/g fresh leaves, and estimates of half-life value ranged from 2.46 to 5.33 days, respectively. In leaves which had not yet emerged or partly emerged at foliar application, 0.16 or 1.08 μg/g of the fungicide was detected when leaves were fully developed, respectively. Foliar application of tricyclazole almost completely protected the completely developed leaves from new infection about for 2 weeks. Also, the leaves newly emerged after fungicide application were somewhat protected. In the greenhouse experiment, tricyclazole showed a completely protectant effect at a concentration above 0.34μg/g, while the effect was not significant at a concentration below 0.20μg/g. The median effective concentration (EC50) of the fungicide was estimated to be 0.24μg/g. Generally, the values estimated in this experiment agreed with the disease progression observed in the field.
