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Disease Detection and Losses

Relationship Between Nitrogen Fertilization, Bacterial Leaf Blight Severity, and Yield of Rice. A. P. K. Reddy, Plant pathologist, All India Co-ordinated Rice Improvement Project (AICRIP), Hyderabad 30, A.P., India; J. C. Katyal(2), D. I. Rouse(3), and D. R. MacKenzie(4). (2)Soil scientist, All India Co-ordinated Rice Improvement Project (AICRIP), Hyderabad 30, A.P., India; (3)(4)Graduate assistant and associate professor, respectively, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 69:970-973. Accepted for publication 22 March 1979. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-970.

In a field study two rice cultivars were compared at various levels of nitrogen (N) fertility in three seasons for both yield and bacterial leaf blight (BLB) severity of rice. High N levels (> 100 kg/ha) increased disease and reduced yield in BLB-susceptible IET 2895. BLB-resistant IET 4141 was least affected by all N levels tested. The relationships between yield and N level and between BLB severity and N level were best described by quadratic and linear functions, respectively. The optimal level of N application (to derive maximum yield with minimum disease effects) was 76 kg/ha for the susceptible cultivar IET 2895. The strategy of eliminating topdressing of rice with N when BLB is severe is discussed in relation to the optimal N level.