Fungal diseases do occasionally appear on a fescue lawn, but there is no reason to panic. Fescue is not particularly prone to disease and most people will grow their lawn for years and years without spraying a fungicide. Occasionally a fungal disease appears under the right environmental conditions, but they usually fade away as the weather changes.
Nonetheless, always be prepared to act if brownpatch, dollar spot, leaf spot, pythium, or rust arrives on your lawn. These diseases are often prevalent in the spring and fall when daytime air temperatures are 60-80°. During these times, it is best to switch to a day-time or early morning irrigation schedule so that the moisture will evaporate quickly.
Fungal diseases are difficult to identify and are often attributed to other problems. In fact, many spring disease outbreaks are ignored until the diseased area grows into a sizeable problem. The best advice is to take a good look at your lawn every couple of days and to be aware of anything abnormal. In general, fungal diseases appear as brown or damaged patches of grass with clearly defined outlines.
If you find a lawn that fits this description, don’t run out and spray the entire lawn with a fungicide. Wait to see if the patch of damaged grass expands over the next day or two. It is quite possible that the fungal disease will run its course naturally. An ‘active’ patch of diseased turf will grow and expand concentrically over a couple of days.