Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Plant, Environmental Management and Soil Sciences

First Advisor

James H. Oard


Sheath blight caused by fungal pathogen Rhizoctonia solani can cause significant yield loss in rice, especially in warm, high rainfall environments. Integrated pest management (IPM) is the key to sheath blight control. This system utilizes disease resistance, pesticides, cultural practices and biological control to control multiple pests. Silicon fertilization is an additional cultural practice that can reduce sheath blight severity and increase grain yield. Studies were conducted in the greenhouse and field to determine the effect of calcium silicate on sheath blight severity, rice grain yield, and leaf silicon concentration. Results in the greenhouse study showed that sheath blight severity was significantly reduced in the cultivar Cypress when calcium silicate was applied to a Crowley silt loam soil. Disease severity for another cultivar Katy was inconsistent in that disease severity was significantly reduced in 1997, but not in 1995. In the same experiment but using reclaimed marsh soil, sheath blight on Katy was significantly reduced in 1997 but not in 1995. In contrast to Cypress grown in Crowley silt loam soil, disease severity was unaffected by the calcium silicate in the reclaimed marsh soil. In the 1995 field study, silicon fertilization on a Crowley silt loam soil in Vermilion Parish, Louisiana, affected yield, y-leaf Si (most recently matured leaf at panicle initiation growth stage) and mature straw Si. Rice grain yield increased 13 percent from a 3.3 Mg ha-1 application of calcium silicate. A significant reduction in sheath blight severity was detected on three different soil types in Louisiana when amended with calcium silicate. The sheath blight severity decreased linearly with slag amendment. These results show that Si fertilization can reduce fungal disease severity, improve grain yield and increase silicon concentration levels in rice tissues. Cultivars differ in their response to the slag amendment in different soils. Silicon concentration in plant tissues can be used as an indicator of yield potential and disease severity in some rice cultivars.