Modelling yield loss in Indica rice in farmers' fields due to multiple pests

Abstract

Surveillance data on grain yield and diseases, insect pests and weeds from farmers' fields for two consecutive wet seasons (1981 and 1982) grouped into dwarf indica (dwarf) and tall indica (tall) rice varieties were subjected to multiple regression analysis. Equations having r2 or R2 ⩾ 0.60 are reported. Bacterial leaf streak alone explained 70% of yield variation in dwarf varieties, leaf blast and bacterial leaf streak together explained a yield variation of 74%. Brown spot and tungro diseases showed little increase in percentage yield variation in tall varieties. Among the insect pests, yellow stem borer alone could explain 69% yield variation in dwarf and 62% in tall varieties. Narrow-leaf weeds contributed more towards yield variation than did broad-leaf weeds. A combination of pests explained variations in yield better than did any individual pest