Golf Course Management

JUL 2018

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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70 GOLF COURSE MANAGEMENT 07.18 Dollar spot is a common and widespread disease of cool- and warm-season turfgrasses throughout the world. e first report of dol - lar spot on turfgrass occurred in 1927, when it was referred to as a "small brown patch" because the disease produces small, straw- colored patches that do not exceed the size of a silver dollar (3). However, the fungus was not officially named until 1937 when F.T. Bennett called it Sclerotinia homoeocarpa (1). Bennett selected this name because he ob - served morphological similarities between the causal agent of dollar spot and other fungi in the genus Sclerotinia. However, over the next four decades, researchers began to cast doubt on the true identity of the causal agent of dollar spot because they observed subtle differences in its morphology and re - productive structures that separated it from other fungi in the genus. Fungi in the genus Sclerotinia have tube- like resting structures called sclerotia. Scle - rotia allow these fungi to survive unfavor- able environmental conditions, sometimes for many years. e dollar spot pathogen does not produce true sclerotia and, instead, forms a flat stroma. As a result, during the 20th century, some scientists concluded that S. homoeocarpa was in fact not a true Sclero - tinia species (2,5) and suggested possible al- ternative genera for this important turfgrass pathogen (for example, Lanzia, Lambertella, Moellerodiscus, Poculum or Rutstroemia). Nevertheless, because sexual spores are ex - ceedingly rare (having only been observed occasionally in the United Kingdom), reclas - sifying this fungus was not possible using the technology available at the time, and the name Sclerotinia homoeocarpa persisted in the literature for more than 80 years. New technology In the 1990s, DNA-based technologies became more prevalent, and S. homoeocarpa was subjected to extensive genetic analy - sis. ese studies supported what had been previously reported: namely, that the dollar spot fungus was almost certainly not a true Sclerotinia species. Unfortunately, despite the mounting evidence, the fungus was still not formally renamed because of its exten - sive genetic variability and because only a few dollar spot isolates were included in these early studies. Recently, a group of researchers from Figure 2. Clarireedia jacksonii. (Top) Numerous infection centers on a creeping bentgrass fairway. Photo by Lisa Beirn (Bottom) Close-up of mycelium. Photo by Katie Diehl

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