Simple method of deciding sampling date for determining whether to control rice leaf beetle (Oulema oryzae Kuwayama)
1999
Hachiya, K. (Hokkaido. Central Agricultural Experiment Station, Naganuma (Japan))
In northern Japan, farmers have to determine appropriately whether to control rice leaf beetle in order to avoid yield loss and overuse of insecticides, because it is the most important pest of paddy field before the heading stage of rice and its occurrence density varies with fields and years. A simple decision-making plan of control necessity consists of determining the sampling time, sampling fields, sampling hills and the procedure for examining population density would be very useful. The present study reports a simple method of deciding the date of egg-mass sampling in order to determine whether insecticide needs to be applied during the succeeding larval injury period. It was possible to forecast the maximum period of egg-mass density, i.e. the proper sampling time, by means of a regression equation for the date of the first day on which the maximum temperature exceeded 25 degrees C nineteen days before the sampling day on average. The solution chart of this equation is convenient for farmers. It was also possible to explain the maximum period of egg-mass density by the effective cumulative temperature above 11.5 degrees C since the end of winter. This method is practical for agricultural guidance offices. The ratio of hatched egg-mass to unhatched egg-mass increased by 12% to 100% (number of hatched masses was equal to unhatched masses) within the maximum of ten days of egg-mass density based on the mathematical simulation. Observation of hatching in paddy confirmed that the sampling time was proper
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