Studies on yield loss and economic threshold of the rice leaffolder Cnaphalocrocis medinalis (GN.) at heading stage of rice in Henan Province, China.
1987
Zhang G.F. | Liu Q.X.
Rice leaffolder is an important rice pest in Henan province, China. In order to obtain better information on the economic threshold for the application of insecticides against leaffolder on rice, during the growing season of 1978-1983, it was decided to evaluate the yield losses due to leaffolder by artificial infestation in different larval density levels at initial heading stage (about 55-60 days after transplanting) to milky ripeness in field plot tests and caged rice at Zhengzhou, Henan province, China. It was found that yield reduction is negatively correlated to larval density. Based on analysis of covariance of the experimental data, the following regression equations were derived. The regression equation of percent leaffold (R) dependent on number of larvae (x) was R = 0.95-0.82 x 0.77. The regression equation of yield-loss (Y) dependent on the percent leaffold (R) was Y = 13.09-20.63 Log R3.99. The regression equation of percent yield-loss (Y) was dependent on number of larvae (x) was Y = -30.92-20.63 Log x 4.65. When the tolerant loss levels were 2%, the control threshold for 3rd-larvae were calculated to be 40-50 larvae/100 hills, or the percentage of leaffold to be 5%.
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