Effect of Calcium Silicate on Blast and Brown Spot Intensities and Yields of Rice. L. E. Datnoff, Assistant Professor of Plant Pathology, Institute of Food and Agricultural Sciences, University of Florida, Everglades Research and Education Center, P.O. Box 8003, Belle Glade 33430. R. N. Raid, G. H. Snyder, and D. B. Jones. Assistant Professor of Plant Pathology; Professor of Soils; and Associate Professor of Agronomy, Institute of Food and Agricultural Sciences, University of Florida, Everglades Research and Education Center, P.O. Box 8003, Belle Glade 33430. Plant Dis. 75:729-732. Accepted for publication 23 January 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0729.

Rice production in the subtropical climate of Florida is on Histosols, which are high in organic matter content and low in plant-available silicon (Si). Broadcast rates of calcium silicate slag were 0, 5, 10, and 15 Mg/ha in 1987 and 1988. In 1987, applications of calcium silicate slag reduced blast by 30.5% and brown spot by 15.0% over the control. In 1988, blast and brown spot were reduced by 17.4 and 32.4%, respectively, over the control. Linear and quadratic equations significantly (P ? 0.05) described the slag-disease and slag-yield relationships. In rice straw samples, only Si, not Ca, significantly increased (P ? 0.05) with increasing slag rates over the control. It appears that reduction in disease intensities can be accounted for only by Si in this study.