Abstract
This study was carried out to determine the economic injury level of the rice leaffolder,Cnaphalocrocis medinalis G.. The damage aspects of rice plant (at tilling stage) by leaf folders at different larval density per plant were studied in pot experiment (24 cm in diameter, 18 cm in height). One leaf folder consumed 6-7 leaves during larval stage. The damage by leaf folders was simulated by cutting off 0, 10, 30, 50, 70, and 90% of leaves before and after heading stage July 15th (at panicle initiation stage) and August 15th (at milk stage), respectively. When leaves were cut before the heading of rice, the linear relationships between the leaf cutting rate (X) and each factors of yield (Y) were as following; for grain maturity it was Y = -9.379X + 83.630 ($R^{2}=0.493$),\;Y = 0.139X + 0.490 ($R^{2}=0.925$) for yield, and Y = -4.880X + 81.116 ($R^{2}=0.665$) for head rice. When leaves were cut after the heading of rice, it was Y = -23.0l4X + 83.589 ($R{2}=0.915$), for grain maturity, Y=0.141X + 3.466 ($R^{2}=0.842$) for yield, and Y = -13.795X + 81.964 ($R^{2}=0.898$) for head rice. We found that when leaf cutting after the heading stage caused more damage than before the heading in terms of yield and yield components. Based on theses results the economic threshold level was estimated to be 30% and 7% leaf loss before and after heading stage.
벼 혹명나방 유충이 벼에 주는 피해를 해석하기 위해 유충 마리당 가해엽수를 조사하고, 생육시기별 절엽 수준(0, 10, 30, 50, 70 및 90%)을 달리하여 수량 및 수량구성 요인을 조사한 결과, 유충 1마리가 유충기간 동안 벼 잎을 $6{\sim}7$개 피해를 줄 수 있는 것으로 조사되었다. 출수전(유수분화기)에는 절엽률과 등숙률과는 Y = -9.379X + 83.630 ($R^{2}=0.493$), 절엽률과 수량감소율과는 Y = 0.139X + 0.490 ($R^{2}=0.925$), 절엽률과 완전미율과는 Y = -4.880X + 81.116 ($R^{2}=0.665$)의 관계가 있었다. 출수 후(유숙기)에는 절엽률과 등숙비율과는 Y = -23.0l4X + 83.589 ($R^{2}=0.915$), 절엽률과 수량 감소율과는 Y=0.141X + 3.466 ($R^{2}=0.842$), 피해율과 완전미율과는 Y = -13.795X + 81.964 ($R^{2}=0.898$) 관계가 있었다. 따라서 출수전보다 출수 후가 혹명나방 피해를 받았을 때 수량이나 수량구성요소에 더 큰 영향을 준 것으로 조사되었다. 벼 혹명나방 피해허용수준은 출수 전(유수분화기)에는 피해엽률 30%, 출수 후 (유숙기)에는 피해엽률 7%였다.
