Development of resistance inDrechslera oryzaeBreda de Haan (Subram. and Jain) was observed under field conditions by continuous treatment of edifenphos. Before the application of fungicide, 96% of the isolates showed a sensitive level, but within 5 years the level of sensitivity dropped and the proportion of resistant populations increased to 52% in 1988. Cross‐resistance studies indicate that edifenphos resistance can be counteracted by spraying mancozeb as an alternative fungicide.