Silicon Suppresses Leaf Spotting on Bermudagrass

Silicon is the second most abundant element after oxygen in the earth's crust, and most soils contain considerable quantities of the element (Savant et al, 1997). However, some soils contain litde plant-available silicon in their native state, and repeated cropping can reduce the levels of plant-available silicon to the point that supplemental silicon fertilization is required for maximum production. Low silicon soils are typically highly weathered, leached, acidic and low in base saturation. Highly organic soils that contain little mineral matter may also contain little silicon, and soils comprised mainly of quartz sand (SÍO2) also may be low in plant-available silicon. Such conditions are presumably prevalent on many sod farms and golf course greens throughout the United States. Plant nutritionists and plant physiologists generally concentrate on improving the management of 13 essential elements (Savant et al, 1997). These include six macro-elements (nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), and magnesium (Mg) and seven microelements (iron (Fe), manganese (Mn), zinc (Zn), boron (B), molybdenum (Mo), chlorine (Cl) and copper (Cu).These elements are considered essential because deficiency of any one of them adversely affects physiological plant function, resulting in abnormal growth and/or an incomplete life cycle. Silicon (Si) is considered a plant-nutrient anomaly because it is presumably not essential for plant growth and development. Soluble silicon, however, has enhanced the growth and development of several plant species including rice, sugar cane, most other cereals and several dicotyledons such as cucumber and watermelon. Higher plants vary in their capacity to accumulate silicon (Datnoff etal, 2001b). Wetland gramineae (rice) absorb silicon as monosilicic acid, Si(OH)4, on a dry-matter basis ranging from 4.6 percent to 6.9 percent, dryland gramineae (sugar cane, cereals, St. Augustinegrass) between .5 percent to 1.5 percent and dicotyledons less than .2 percent. Therefore, silicon can be accumulated from soil by plants in amounts that are several folds higher than those of other essential macroor micronutrients. For example, silicon accumulation may be twice that of N in rice. Silicon amendments also have proved effective in controlling both soil-borne and foliar fungal diseases in cucumber, rice, sugar cane, turf and several other plant species (Datnoff et al, 2001b). In rice, silicon has been demonstrated to control rice blast, as effectively as a fungicide and even reduce the rate or number of fungicide applications (Datnoff et al, 2001a). In addition, partially blast-resistant rice cultivars amended with silicon had their resistance augmented to the same level as those considered completely resistant (Seebold et al, 2000). Because this element had proven effective for controlling rice blast (Datnoff et al, 2001a; Datnoff et al, 1997; Savant et al, 1997), Datnoff and Nagata (1999) studied the effect of silicon on gray leaf spot development in St. Augustinegrass under greenhouse conditions. They demonstrated that silicon significantly reduced area under the disease progress curves (AUDPC) for gray leaf spot between the 44 percent and 78 percent, final Silicon accumulation in the leaves of bermudagrass (173) FIGURE 1