Greenhouse studies assessed the pathogenicity of Fusarium pallidoroseurn-on rice leaffolder (LF) Cnaphalocrosis medinalis Guenée at 28.5°C and between 88 and 90% relative humidity. The pathogen was tested at spore concentrations of 0-1×10 7 conidia mL-1. A stock solution of 1 mL was diluted with sterile distilled water, i.e., 100, 1000, etc., which meant 1 part of the fungus suspension was diluted in 99 or 999 parts of water. Thirty third-instar larvae were dipped for 2 to 3 s in each concentration. Treated larvae were transferred to filter paper and incubated in a petri dish containing fresh rice leaves. Mortality was determined after 1 wk of incubation and the percentage adjusted using Abbott's formula. Probit analysis showed that 5.49 × 103 conidia mL-1 was the effective concentration for LD50 of F. pallidoroseum.