Study of Factors Affecting Growth and Development of Narrow Brown Leaf Spot of Rice Caused by Cercospora janseana (Racib.) O. Const.

Abstract

Studies evaluated the effects of planting date, cultivar susceptibility, fungicide application timing, nitrogen management, and tillage practices on the severity of narrow brown leaf spot of rice (NBLS) caused by Cercospora janseana. All factors evaluated affected NBLS severity. The mid-April planted rice had less NBLS as compared to mid-May, late planted rice. Propiconazole fungicide (Tilt) application at panicle initiation or early boot stage was found equally effective in terms of disease reduction in mid-April planting while panicle initiation stage was the best time to apply fungicide in the late planting (mid-May). Early onset and higher severity of NBLS was observed on very susceptible cultivars (Cheniere and CL131) and delayed and least on resistant cultivars (Della and Presidio) at both the planting dates. The very susceptible to moderately susceptible cultivars produced similar yields under lower disease pressure (mid-April). Under, higher disease pressure, yields were lower, and variable responses to NBLS were detected among cultivars that did not relate to the susceptibility ratings based on disease severity. NBLS severity was higher when no nitrogen or excessive nitrogen was applied in susceptible and moderately susceptible cultivars, but no effect of nitrogen was observed in resistant hybrid LAH10. Split nitrogen applications (84/50 kg/ha) resulted in lower NBLS severity in susceptible cultivars compared to single nitrogen application. NBLS development was higher in a stale seed-bed as compared to conventional seed-bed system and increased at higher seeding densities. At a low seed density, NBLS severity was not significantly different between the two tillage systems. The demonstrated effects and interactions of host resistance, fungicide application, and cultural practices on NBLS severity indicate the potential for integrated disease management of this increasingly important rice disease