The Wow Factor, Seashore Paspalum and Dollar Spot

I hear or read a lot about the "Wow" factor of seashore paspalum (Paspalum vaginatum) in reference to the vibrant green color of the grass, but not so much about the other "Wow" factor associated with seashore paspalum -- it is highly susceptible to dollar spot. And it is dollar spot season now in many parts of Southeast Asia, with temperatures cooling down to 22 or 23 °C at night (about 73 °F) and rising to about 32 °C (about 90 °F) in the afternoons. During the hotter times of the year, when nighttime temperatures are warmer and rain falls more frequently, I see less dollar spot.

Why is that? You may not think these temperatures are cool, but this is the coldest time of year at places such as Bangkok, Ho Chi Minh, Manila, and Hong Kong, so the warm-season grasses (including seashore paspalum) grow a little bit slower. Also, this tends to be the dry season in parts of Southeast Asia, and seashore paspalum eventually slows its growth under deficit irrigation (applied irrigation less than evapotranspiration). So we have plants that are growing a little bit slower, slightly cool nights at an ideal temperature for the dollar spot pathogen to grow, and a susceptible host. It doesn't snow here (One of the many reasons I chose to work in Asia was because of the salubrious climate, so I savor my memories of snowy winters while I enjoy my winters in tropical climates) but sometimes the dollar spot is so severe that a fairway can look as if a light snow has fallen. That is the other "Wow" factor of seashore paspalum.

Seashore paspalum is generally quite susceptible to dollar spot, although there are differences among cultivars. Dr. Bryan Unruh's research with different seashore paspalum varieties in Florida (the research paper is available for download here) shows big differences among cultivars. SeaIsle Supreme was especially susceptible to dollar spot; SeaDwarf and SeaSpray were among the varieties with the lowest incidence of dollar spot. Dr. Philip Harmon has written a good reference on seashore paspalum diseases. That article was just published in the Green Section Record (download Challenges and Opportunities: Disease Management for Seashore Paspalum in Florida).

In the warmer parts of Southeast Asia, where the nighttime temperatures rarely drop below 20 °C, dollar spot on seashore paspalum can usually be managed (at least on tees and fairways) with minimal fungicides. If we can accept some damage from disease, applications of fertilizer and water to stimulate more rapid growth will usually allow the turf to grow faster than the dollar spot can damage it. In cooler parts of Asia, where seashore paspalum growth is more restricted in winter, then fungicides may be required to control the disease. On greens there is rarely a situation when the risk of severe dollar spot infection can be tolerated, so fungicides are almost always required on a preventative basis.

My management suggestions are:

• monitor the turf growth rate and scout for dollar spot daily
• on fairways and tees, apply fast release nitrogen (sources such as ammonium sulfate, urea, or calcium nitrate work well) to stimulate growth when dollar spot infections are more than you wish to tolerate
• ensure that soil moisture levels are in an optimum range for seashore paspalum growth
• on greens, follow the same practices and use fungicides as necessary to control and prevent additional infections

One thing to note is that bermudagrass and zoysiagrass are relatively immune to dollar spot in Southeast Asia. On golf courses I have never seen that pathogen on those grasses. So keep that in mind when choosing grasses for your course. If seashore paspalum is chosen for the "wow" factor of color, you may also see the "wow" factor of snowy fairways. With zoysia in January (see below), very little maintenance is required but the grass provides a great surface.