Effects of silicon on gray leaf spot development of perennial ryegrass turf

Studies were conducted to investigate the use of silicon in integrated management of gray leaf spot caused by Magnaporthe grisea in perennial ryegrass (Lolium perenne L.) turf. The ability of perennial ryegrass to accumulate silicon was determined in greenhouse experiments in two soil types (peat:sand mix and Hagerstown-silt-loam) amended with two sources of silicon (calcium silicate slag with 43.3% of SiO2 or wollastonite with 50% of SiO2) at six rates (0, 0.5, 1, 2, 5 and 10 metric ton/ha). Perennial ryegrass was determined to be a silicon accumulator and tissue silicon content increased up to 4% in this study. The tissue silicon content (%) of perennial ryegrass increased with increasing rates of silicon applications and was also influenced by the soil type and source of silicon.; The effects of silicon on gray leaf spot development were evaluated in controlled environment chambers, semi-field conditions, and on golf courses. In controlled environment chamber experiments, nine-week-old perennial ryegrass grown in peat:sand mix and Hagerstown-silt-loam, amended with wollastonite and calcium silicate slag, at six rates (0, 0.5, 1, 2, 5 and 10 metric ton/ha) were inoculated with M. grisea (35 x 10 3 conidia/ml H2O). The results showed that disease incidence and severity were reduced compared to the non-amended control by silicon amendments. Furthermore, disease incidence decreased with increasing levels of silicon. Disease incidence also decreased with increasing tissue silicon content. Similar trends were observed in semi-field conditions when six-week-old perennial ryegrass were placed in holes made with a cup-cutter among established perennial ryegrass turf and inoculated with M. grisea (60 x 10 3 conidia/ml H2O).; The effects of silicon fertilization on gray leaf spot development were evaluated on two golf courses in Pennsylvania. Site 1 had alfisols with a soil silicon level of 31 mg/kg while Site 2 had ultisols with 18 mg/kg of silicon in the soil. Silicon was broadcasted as a top dressing and incorporated by core-aerification. The plots were inoculated with M. grisea (60 x 103 conidia/ml H2O) nine weeks after applications of silicon. Results showed that the area under the disease progress curve (AUDPC) and final disease severity were significantly reduced by 5 and 10 metric ton/ha of silicon compared to the non-amended control in Site 1. All rates of silicon reduced AUDPC, final disease severity and the rate of disease progress compared with the non-amended control in Site 2. Disease severity at individual assessment times was also reduced by silicon amendments between 4-10 weeks after inoculations in both sites. Results clearly showed a greater magnitude of gray leaf spot reduction in the silicon deficient Site 2 compared with Site 1.; Studies were conducted on golf courses to determine whether silicon could suppress gray leaf spot as effectively as recommended rates of two commonly used fungicides to manage gray leaf spot.