Although dollar spot has been around since the 1920s, it remains one of the most expensive diseases to manage. Photo courtesy John Kaminski

The bottom line is disease management is not a stationary target. Turfgrass managers must keep current with the latest information on emerging diseases and the latest products available. They must also continue to review fundamental concepts such as disease lifecycles as well as the biology of the turfgrass pathogens. Only when a manager can grasp all the concepts surrounding the pests and current chemical and cultural management options can they make the best decisions when it comes to keeping their turf healthy.

If nothing else, the evolution of turfgrass diseases will result in two things: it will ensure only those that keep up with all of the changing information are able to successfully control their disease problems, and it will ensure turf pathologists around the world are forever employed.

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Breeding programs continue to help improve the tolerance of turf to various diseases. Photo courtesy John Kaminski

Another major factor in the evolution of disease management is the ability (or lack thereof) to manage pathogen resistance to fungicides. Rotation of chemical classes, proper use rates, and tank-mixing are a few ways to help delay or prevent the onset of resistance. Other factors, however, play an important role in the efficacy of the fungicides.

One of those factors is the timing of the applications. Many law-makers and those who do not really understand the biology of pests or the management of turf often suggest that waiting until symptoms appear is the most environmentally sound way to use pesticides. This author gets into these discussions routinely and does his best (although it sometimes may fall on deaf ears) to explain why this may not always be the case.

As an example, dollar spot is a prominent disease on golf courses and can occur over extended periods. Targeting this disease preventively is an excellent way to keep inoculum levels down and therefore prevent damage from occurring. Curative control (i.e. after symptoms have developed) is often difficult and comes at the expense of higher pesticide use rates, shorter application intervals, and increased potential for resistance development. In these cases, letting the disease develop before implementing a chemical control can actually result in an increase in pesticide use and loss of currently effective products through resistance.

While this concept can sometimes be difficult for those who do not understand disease lifecycles and epidemiology, it is the same concept that allows turf professionals to choose which diseases should be treated preventively versus curatively. Diseases such as take-all patch, dollar spot, summer patch and the snow moulds are more effectively managed when pesticides are applied preventively. On the other hand, diseases such as brown patch and even rust to some extent can quickly be squelched with a curative application.

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Understanding basic information about fungicides is critical in resistance management. Photo courtesy John Kaminski

Between old diseases emerging as more prominent problems, uncommon pathogens becoming more common, and entirely new pathogens appearing, the turfgrass pathology community is constantly evolving.

How does this impact turf professionals and the management of their issues? If they are one of the fortunate superintendents in the areas where pesticide restrictions are limiting the ability to manage the diseases, they are lucky. If they do not have the ability to do anything about it, then there is not much that can be done. The reality of disease management under the high pressure observed on golf courses is often too much to handle soley through changes in cultural management programs and, unfortunately, biological controls have been met with limited success in high maintenance turf.

If there is still a limited arsenal of control options available, then he or she may be one of the lucky ones. However, this does not mean reliance on chemical control should be the first option. Choosing sound cultural practices for the species being managed is the first place to make adjustments. Growing the healthiest plant possible is going to make the fungicides more effective.

Read the full article: The Evolution of Turf Diseases

Bentgrass dead spot represented an entirely new disease caused by a previously undescribed pathogen. Photo courtesy John Kaminski

Although grey leaf spot was a minor disease in the southern United States, it was known. What about the development and presence of entirely new problems no one has ever heard about? It certainly happens with evolution and is no different in turf.

A good example of a new pest problem emerging in turf occurred on creeping bentgrass putting greens in the late 1990s. This author remembers starting his graduate program at the University of Maryland and seeing the first case of bentgrass dead spot on the second day. When his mentor and advisor Dr. Peter Dernoeden first looked at the sample under the microscope, he was quite surprised—he had never seen anything like it in the past, and was excited to figure out exactly what he was looking at.

After a few months of isolations and a few years of data collection and molecular investigations, it was determined that not only was this pathogen new to turf, but it also represented an entirely new species within the genus Ophiosphaerella. How can a new species suddenly show up on 10 different golf courses from six different states in a single year? Although this author never definitively determined how the pathogen made its way to so many courses at the same time, the fungus was later found on a bamboo-like plant used for packing material in shipments from Asia. This could simply be a case of putting a previously unreported fungus in close proximity to a susceptible host and letting nature do the rest.

However, this was not the only isolated incidence that occurred in the past decade or so. Rapid blight (caused by Labyrinthula terrestris) was another previously unreported pathogen in turf, but quickly made its way onto golf courses in the Western United States where high salinity water was being used.

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Identification of turfgrass diseases based on a combination of disease symptoms and pathogen signs is critical for a proper diagnosis. Photo courtesy John Kaminski

By taking a closer look at the influence turfgrass diseases have had on management practices, it does not take long to realize their importance. In the 1970s and 1980s, Kentucky bluegrass was a common turfgrass species on fairways throughout the mid-Atlantic region of the United States. During that period, summer patch (caused by Magnaporthe poae) became such a devastating problem that golf course superintendents had to figure out an alternative species to prevent the exorbitant costs associated with chemical control of the disease. It was time for a species switch.

Perennial ryegrass was a logical solution at the time. The rapid germination rate, dark green colour, and lack of susceptibility to M. poae made it a logical and cost-effective replacement for Kentucky bluegrass. The conversion seemed to be doing well, and even the high-handicap golfers liked the fluffy lies that would allow them to easily sweep the ball off the fairway. Unfortunately, unexpected outbreaks of an uncommon disease in the mid-1990s took its toll on those that switched.

Read the full article: The Evolution of Turf Diseases