SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.
Issue link: https://read.dmtmag.com/i/232221
While there are many different modes of action available, many of the most popular fungicide products for turf contain ingredients with the same mode of action. This brings up the potential problem of fungicide resistance. Fungi are highly diverse and repeatedly spraying the same mode of action selects for any resistant individuals that happen to be present in a given population. If they are, then they multiply while susceptible ones are killed and soon the majority of the fungal population is resistant and the fungicide stops working to prevent disease. Modern fungicides tend to have very specific sites of action in fungi. For example, many target just one enzyme in a fungus, binding to it and making it no longer able to function. This is good, since it means that the fungicides are very specific and less likely to cause harm to non-target organisms. But it is also bad from a resistance standpoint because it means that all that has to happen for a fungus to become resistant is a small change in that one enzyme such that the fungicide can no longer inactivate it. This happens in nature and often just one or two mutations are enough to make a fungus resistant. Because of the potential for many turfgrass diseases to become resistant to fungicides, managers have been advised for years to rotate modes of action or to tank mix more than one mode of action at a time in a given application. The international Fungicide Resistance Action Committee (FRAC, www.frac.info) maintains a listing of currently registered fungicide active ingredients and their modes of action. They are sorted into groups of individual ingredients sharing the same mode of action and each group is assigned a unique code. Recently, manufacturers have begun placing the FRAC mode of action group codes on their product labels. This is a tremendous help to the turf manager trying to manage resistance as now it is immediately obvious which products contain ingredients that have the same mode of action. Now it is possible to tell at a glance whether rotating to a given product will actually mean switching modes of action. It is important to remember, though, that even though resistance has been documented in many turfgrass diseases, not every failed fungicide application is due to resistance. It is still more common to see fungicides fail due to improper calibration, reading labels incorrectly, not using enough spray volume and/or the wrong nozzles, and plain old misdiagnosis of the disease. Nevertheless, if you suspect resistance, it is a good idea to contact your local Extension agent or plant pathology lab. They will be able to assist you in identifying possible problems with your fungicide application and, if needed, can collect samples and screen them for resistance. n Dr. Dave Han is an associate professor of Crop, Soil and Environmental Sciences at Auburn University and an Extension Specialist at the Alabama Cooperative Extension System. www.stma.org January 2014 | SportsTurf 31