Torsiello's Turf Talk: Dollar Spot - The Bane of Golf Course Superintendents

By: John Torsiello

Get a load of this stat: In Wisconsin it has been reported that golf course superintendents typically spend 60 to 75 percent of their chemical budgets spraying for dollar spot. To be sure, in other states, the expenditure to prevent and treat dollar spot is also one of the biggest line items in a course's maintenance budget. So, yes, the turf disease can be a big deal, a lot more than a dollar's worth of trouble.

The disease affects the majority of turfgrass species, and is active under a wide range of temperatures. Dollar spot is the most common turfgrass disease in North America, with the exception of the Pacific Northwest and western Canada. It is caused by the fungal pathogen sclerotinia homoeocarpa, in the sclertiniaceae family. The pathogen blights leaf tissues but does not affect turf grass roots or crowns. Disease symptoms commonly result in poor turf quality and appearance and it occurs from early spring through late fall, but is most active under conditions of high humidity and warm daytime temperatures between 59 and 86 degree Fahrenheit and cool nights in the spring, early summer and fall. The disease infects by producing a mycelium, which can be spread mechanically from one area to another.

Here is what some experts told me recently about the problem:

Dr. James Kearns, Turfgrass Pathologist with North Carolina State University's Department of Plant Pathology, says if superintendents allow the disease to develop and infection centers to sit over winter it provides an excellent source of inoculum for epidemics the following year. "Moreover, for those that experienced snow mold pressure, applications in the fall for dollar spot will help limit snow mold development as well."

As far as winter temperatures, he adds, the dollar spot fungus can survive readily in foliage and most likely thatch in extreme weather conditions. "We examined this in a three-year study in Wisconsin and we were always able to find the fungus even after the harshest winter. As an example, we can store the dollar spot fungus on filter paper at -112 Fahrenheit and it will survive if it has had an opportunity to dry down."

Todd Hicks, Program Coordinator of Turfgrass Pathology in the Department of Plant Pathology at Ohio State University, says if an area had a late fall and extended time for dollar spot activity there could be two possible scenarios. "One, it gave you more time to clean up disease if present and go into winter in a health condition. Or, two, if there was dollar spot and you did not manage the disease, the turf would be in poorer condition going into winter and with disease that will be more difficult to manage the next year."

Okay, that's looking ahead to the end of the year when you can get the jump on dollar spot. But what about now? Well, spring weather is crucial in regards to the possibility of dollar spot outbreaks. A mild, humid spring, as some regions of the U.S. have experienced, will help the disease to readily develop. Superintendents should watch RH values and use temperature only as a guide. Says Dr. Kearns, "We know dollar spot can develop from temperatures ranging from 50 to 95 Fahrenheit if relative humidity is sufficient."

Joseph Rimelspach, Program Specialist of Turfgrass Pathology in the Department of Plant Pathology at Ohio State University, says watch out for a warmer than normal spring with moisture and high humidity. It will often enhance early dollar spot development that potentially could be severe.

Dr. John Inguagiato, Assistant Professor, Turfgrass Pathology in the Department of Plant Science and Landscape Architecture at the University of Connecticut, says he and other researchers consider dollar spot epidemics "polycyclic." In other words, as long as favorable conditions for disease exist the pathogen will continue infecting its host and quickly grow its population and increase the severity of the epidemic. The severity of dollar spot epidemics this year will most likely have more to do with springtime temperature and humidity levels than anything that happened over the winter.

Dr. Geunhwa Jung, Associate Professor of Turfgrass Pathology/Breeding at the Stockbridge School of Agriculture at the University of Massachusetts, says superintendents should be aware of the grass species on their course. Creeping bentgrass is the most susceptible species to dollar spot. Superintendents should also closely monitor "indicator" or "hot spot" areas in which dollar spot historically shows up first. These spots are likely to have extended leaf wetness because of poor drainage, more morning shade, or a lack of air movement.

Adam Moeller, agronomist for the United States Golf Association Green Section's Northeast Region, says dollar spot severity should be objectively assessed if an outbreak occurs. In many cases, a very small outbreak does not warrant an extra fungicide application outside of a traditional preventative program. Superintendents should increase efforts to manage the disease culturally by dragging fairways to remove dew on days when mowing is not performed, and perhaps increase the input of nitrogen into the soil.

Dr. Inguagiato advises to double-check sprayer output to ensure applying fungicides at the proper rate in on-e to two-gallon, 1,000-foot two-carrier volume and flat fan nozzles that produce a medium to coarse droplet size. "If dollar spot damage is evident, consider using a water-soluble nitrogen source to grow out of damage. When disease outbreaks occur, we often find it necessary to temporarily shorten fungicide re-application intervals to arrest further disease development."

If dollar spot infection occurs and curative action is required, Dr. Jung advises to use tank-mix contact and systemic fungicides to stop infection and maintain a regular (14 to 21 days) application interval following initial curative application. However, selection of the proper fungicide classes is critical since resistance to three fungicide classes, says Dr. Jung. "Resistance has not been reported to the SDHI (succinate dehydrogenase inhibitors) fungicide class (boscalid, fluxapyroxad, and penthiopyrad) and this class provides very good dollar spot control."

Dr. Paul Koch, Assistant Professor in the Department of Plant Pathology in the Molecular and Environmental Toxicology Center at the University of Wisconsin-Madison, says once dollar spot is present a mixture of fungicides should be applied as quickly as possible to bring the disease under control. Use a contact fungicide to quickly limit the spread of the current infection, and a penetrant fungicide to protect emerging leaf tissue. Reapplication intervals should then be tightened for several weeks following the outbreak to allow for a full recovery of the turf.

John Torsiello is an editor/writer living in Connecticut. He has written extensively about all aspects of the golf industry for a number of national and regional publications. He is a regular contributor to "Golf Course Industry," "Lawn and Landscape," "Golfing" and "Fairway Living" magazines as well as various online publications. He has strong, ongoing relationships with industry professionals and has worked closely with course owners, architects, developers, course superintendents and general managers around the country. He has won a number of awards for his writing, including first place from the Turf and Ornamental Communicators Association for a piece that appeared in "Golf Course Industry" magazine.

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