Silicon, applied as calcium silicate slag (20% Si), was evaluated for its potential to suppress gray leaf spot (Magnaporthe grisea) and increase plant growth in newly planted St. Augustinegrass in the summers of 2000 and 2001. Calcium silicate was applied (1,000 kg Si/ha) to three sites that contained Si-deficient Histosols prior to sprigging St. Augustinegrass, cv. Floratam, in southern Florida. This treatment was compared with foliar sprays of chlorothalonil, calcium silicate plus chlorothalonil, and an untreated control. Immediately after planting, applications of chlorothalonil (720 g/liter) were made every 10 days for a total of seven sprays at a rate of 7.6 kg a.i./ha with a commercial sprayer. Based on area under the disease progress curve (AUDPC) values for the treatments calcium silicate alone, chlorothalonil, and calcium silicate plus chlorothalonil, gray leaf spot was reduced by 7, 65, and 68% at site one, 28, 34, and 59% at site two, and 41, 55, and 68% at site three, respectively when compared with the untreated control. The application of calcium silicate alone significantly reduced the final AUDPC of gray leaf spot when compared with the control at site two only. However, when disease severities were analyzed by week, the calcium silicate treatment significantly reduced the percentage of disease at weeks 2, 6, and 8 at site one and weeks 3 to 8 at site three when compared with the control. The final percent bare ground coverage for St. Augustinegrass was increased significantly using calcium silicate by 17 and 34% over the control at sites one and two, respectively (P ≤ 0.05). Silicon was the only element to significantly increase in the leaf tissue for treatments amended with calcium silicate. Levels of Si in leaves for treatments amended with calcium silicate were from 1.2 to 1.3%, while those not receiving calcium silicate had only 0.6 to 0.7%. Amendments with calcium silicate slag for St. Augustinegrass sod production on Si-deficient soils may be an option to reduce gray leaf spot development in newly sprigged fields and promote earlier ground coverage of grass when the environment is favorable for disease.

Isolates of Curvularia lunata, C. geniculata, Bipolaris hawaiiensis, and B. cynodontis were tested for pathogenicity on the hybrid bermudagrass cultivars Tifdwarf, TifEagle, and FloraDwarf at 20 and 30°C. Curvularia lunata, C. geniculata, and B. hawaiiensis produced some minor leaf tip necrosis at the cut ends of leaves 24 to 48 h after inoculation. Bipolaris cynodontis produced significant tip dieback and leaf spotting on all three cultivars at both 20 and 30°C, and disease severity was higher at 20°C than at 30°C. With C. lunata, C. geniculata, and B. hawaiiensis, occasional leaf-spotting occurred only on senescing, older leaves. Bipolaris cynodontis is considered pathogenic on bermudagrasses, while C. lunata, C. geniculata, and B. hawaiiensis are considered senectopathic, able to incite disease only in senescing plant tissue. Curvularia lunata and B. hawaiiensis resulted in higher disease severity at 30°C than at 20°C, indicating that these species are senectopathic at higher temperatures. Accepted for publication 29 September 2006. Published 19 January 2007.

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Fungicides were evaluated for control of fairy ring symptoms in bermudagrass maintained at golf course putting green height. In 2004, Heritage and ProStar fungicides tank‐mixed with the nonionic soil wetting agent AquaGro had significantly higher quality ratings and lower percent necrotic ring symptoms compared to the untreated check. Insignia significantly reduced the percent necrotic ring when compared to the untreated check although the mean quality ratings were significantly lower than those for Heritage or ProStar treatments. In 2005, when fungicides were applied closer to the onset of symptom development, with the soil surfactant Magnus, Insignia reduced percent necrotic ring symptoms and increased turf quality to levels at or above those of Heritage or ProStar‐treated plots. In 2005, Insignia + Magnus resulted in higher quality than Insignia alone. In both 2004 and 2005, neither of the soil surfactants alone was effective at reducing fairy ring development. Treatments containing Insignia (two trials in 2005) and Heritage (one trial in 2005) continued to have significantly higher turf quality, even 6 or 7 weeks after the last fungicide application.

If you maintain St. Augustinegrass (Stenotaphrum secundatum) in Florida, its possible that gray leaf spot, caused by the fungus Magnaporthe grisea (Pyricularia grisea), will be a problem in your lawn or sod field. Research has proven the effectiveness of amendments of silicon (Si) to soils that are deficient in soluble Si (<25 mg/L) for control of diseases on a number of hosts including rice and sugarcane, which are regularly fertilized with Si in south Florida. This document is PP-67, one of a series of the Plant Pathology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date: July, 2003. https://edis.ifas.ufl.edu/pp114