Recent weather patterns of cool/cloudy/rainy weather across much of North Carolina have been perfect for foliar diseases such as Bipolaris leaf spot and Pythium blight on bermudagrass putting greens.
We have received many samples in the past week at the NC State Turf Diagnostics Lab that were devastated by the fungus Bipolaris cynodontis. Bipolaris leaf spot is most severe on turf that is growing slowly due to adverse weather conditions or improper management practices. Shaded areas with little or no air movement result in weak turf and extended periods of leaf wetness that favor disease development. Deficient or excessive nitrogen, excessive thatch, extended periods of leaf wetness, and low mowing heights are factors that encourage the development of leaf spot diseases. The fungus is easily spread by mowers, wind, and/or rain.
We have also diagnosed many bermudagrass samples this week with Pythium blight in conjunction with leaf spot or acting alone. The symptoms are a rapid foliar blight that initially has a purple coloration but then fades to tan. Spreading by mowers or in drainage patterns usually occurs as well.
Pythium blight in October? Yes, you read it correctly, it is Pythium blight in October. There are a lot of Pythium species that can infect grasses. Most people are familiar with P. aphanidermatum that causes Pythium blight on the cool season grasses during hot summer weather. However, there are other Pythium species that grow during cool or cold weather. We don't know what species is causing this outbreak yet, but obviously it grows well during cool weather and has a competitive advantage over the bermudagrass under these conditions.
Fungicide treatments may not always be necessary to control Pythium blight on bermudagrass, as dry and sunny weather usually put a stop to it very quickly. However, if the forecast is calling for extended periods of wet and cloudy weather, an application might be a good idea. Any strong Pythium fungicide should do a good job.