Research in Plant Disease 2008;14(1):21-25.
Published online April 30, 2008.
벼 잎도열병 피해해석에 의한 경제적 방제수준 설정
예완해, 박홍현, 남영주, 김설아, 이정희, 심홍식, 김용기, 이용환, 이영훈
 
Establishment of Economic Threshold by Evaluation of Yield Component and Yield Damages Caused by Rice Leaf Blast (Magnaporthe grisea)
Wan Hae Yeh, Hong Hyun Park, Young Ju Nam, Seol A Kim, Jeong Hee Lee, Hong Sik Shim, Yong Ki Kim, Yong Hwan Lee, Yeong Hoon Lee
Abstract
This study was conducted to decide disease incidence level of rice leaf blast required for reasonable fungicide application in paddy field. We induced the disease development by inoculating rice blast pathogens on rice seedlings (Jinmibyeo) in the greenhouse and transplanting the infected seedlings in the field two weeks after rice plants were transplanted. We scored the disease incidence, grouped and marked according to degree of percentage of diseased leaf area at maximum stage of disease development. The percent diseased leaf area (PDLA) had negative correlations with panicle number per hill, ripened grain (%), and total yield; their correlation coefficients (r), -0.97**, -1.00** and -0.96**, respectively. However, it had positive correlations with spikelets per panicle and thousand grain weight; their correlation coefficients (r), 0.98** and 0.98**, respectively. Gain threshold (GT) calculated based on control cost and market price was estimated to be 8.35. Economic injury level (EIL) obtained based on GT and coefficient of damage of regression equation between disease incidence and the different yield components; panicle number per hill, spikelets per panical, ripened grain(%), thousand grain weight and yield were 41.8, 9.7, 19.1, 291.1 and 3.4%, respectively. Economic threshold (ET) for yield was 2.7% (3.4%(EIL) × 0.8) on PDLA. These results suggest that application of fungicide is necessary when two under leaves are almost covered with lesions or contained more than twenty large lesions under leaves at maximum tillering stage.
Key Words: Economic threshold, Fungicide application, Leaf blast, PDLA, Rice


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