Optimal tuning of preventative fungicide applications for fairy ring caused by Vascellum pratense in creeping bentgrass putting greens

• Published in: Phytopathology 2009-06, Vol.99 (6), p.S199-S199
• Main Authors: Miller, G L, Tredway, L P
• Format: Article
• Language: English
• ISSN: 0031-949X

Fairy ring symptoms occur around the outer edge of a subsurface fungal colony, where density of mycelium is greatest. This mycelial mat can result in soil hydrophobicity, resulting in turf loss and making delivery of curative fungicide applications difficult In 2007 and 2008, single spring applications of the low and high rates of triadimefon and tebuconazole were evaluated for control of fairy ring on 'A-1' creeping bentgrass maintained under putting green conditions. Each treatment was applied when 5-day average soil temperatures (2 inch depth) reached 10C, 13C, 16C, 18C, 21C, or 24C. Treatments were arranged in a split plot design with timing as main plots and fungicides as subplots. Fungicides were applied in 0.08 L H sub(2)O m super(-2) and immediately watered in by hand with 6 mm of irrigation. Surfactants were not tank-mixed with fungicides, but Cascade Plus (Precision Laboratories, Waukegan, IL) was applied on monthly intervals to prevent localized dry spot. Visual and objective disease severity ratings were taken every 7-14 days. Data were subjected to analysis of variance and means were separated with the Waller Duncan k-ratio t-test (k = 100). Fairy ring symptoms were most severe in 2007 due to drought conditions. In 2007, symptoms began to appear prior to the 24C application timing, rendering these treatments curative in nature. In both years, all preventive fungicide treatments resulted in adequate control of fairy ring in early summer, but suppression failed later in the season. In 2007, plots treated with the low rate of triadimefon had higher disease severity in late summer than those treated with the high rate of triadimefon or either rate of tebuconazole. Area under the disease progress curve (AUDPC) was lowest for fungicides applied at 13C, 16C, and 18C in 2007. In 2008, AUDPC values were highest for the earliest (10C) and latest (24C) application timings.