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Effect of Dew Period and Temperature on the Ability of Exserohilum monoceras to Cause Seedling Mortality of Echinochloa Species

In greenhouse and controlled environment experiments, disease development and mortality of Echinochloa crus-galli, E. colona, and E. glabrescens caused by Exserohilum monoceras were affected by duration, frequency, and timing of dew period, as well as by dew-period temperature and post-dew temperature. When adequate dew was provided, 100% mortality occurred for all three Echinochloa spp. over the broad dew-period temperature range of 20 to 30°C. The effect of post-dew temperature on disease development varied with the initial dew period. The minimum dew period to achieve 100% mortality was 16 h for E. colona, 12 h for E. crus-galli, and 8 h for E. glabrescens. Increasing dew period enlarged the range of temperature for maximum efficacy, whereas the use of optimum dew-period temperature decreased the dew period requirement. Delaying the initiation of the dew period by 24 h did not adversely affect disease development. Increased disease development occurred for inoculated seedlings treated with repetitive dew periods of shorter duration than the optimal period. These findings characterize one of the epidemiological requirements, i.e., dew requirement, needed to assess the potential of E. monoceras for the control of Echinochloa spp. in rice.