I have a large patio with 4' x 4' concrete squares divided by 3" gaps that are planted with creeping thyme. The thyme is watered using an automatic underground watering system. The patio is in full sun most of the day (with a couple of areas that are in part shade). The thyme was planted about a year ago and has done great until just recently. I am now noticing that in certain areas, it is turning black. The black patches appear to start below the surface...at the soil level but eventually take over the whole area. When you touch the black areas, they are dried out and brittle.

I can't seem to find anything anywhere that can identify the problem I am having, therefore, I don't know what to do to treat it. Is it root rot? Or something else? I really haven't done anything differently lately, however, it has been hot. Any help would be appreciated! Thanks