By Stephanie R. Butcher, County Extension Agent

Question… My bermuda grass lawn looks strange this fall. It has a mottled appearance. I didn’t apply anything or do anything out of the ordinary this year. Why does it look like this?

Agent: If your lawn looks like the one in this picture, then there is nothing to worry about. Your lawn is just going into dormancy. The interesting pattern is sometimes referred to as ‘tiger stripe’. You might be thinking, “My warm season lawn goes dormant every winter, and I haven’t seen it like this before?”

There are several reasons why many lawns looked like this over the past several weeks, but they are all related to warm season grasses going into dormancy. Several things have to occur at the same time in order for this to happen. Research shows that the determining factor for patterns like this have to do with temperatures (air and soil) and the height of the turf grass during our first cold snap.

Without getting into all of the complicated scientific formulas for why this phenomenon happens, it is basically caused by a difference in the way heat is distributed throughout the individual blades of grass—called ‘thermal convective motion’. See what I mean about not getting too complicated?

We had an early and quick cold snap this year. In fact, it was the earliest first frost date that we’ve had in several years. We went from extremely warm air temperatures to extremely cold air temperatures very quickly. Soil temperatures were still pretty warm and provided a buffer with rising warm air that protected some turf grass from the cold air moving through the grass canopy. In lawns with a lower mowing height, you may not have seen this pattern, whereas lawns with a higher mowing height would have shown the pattern.

So why don’t we see this every year? Because when temperatures decrease gradually and we have a later frost date, then soils have already cooled down. Usually by the time we have our first real cold snap, the cooler air is more evenly distributed through the grass canopy which causes grass to go dormant more evenly across your lawn.

One word of caution about warm season grasses and winter dormancy. If you take the opportunity to treat winter annual weeds with a non-selective herbicide in your bermuda grass lawn after it goes dormant, make sure that your bermuda grass is completely dormant before doing so.

Even though bermuda grass may appear dormant (brown grass), sometimes our winters don’t get cold enough for the grass to go completely dormant. Check the turf grass rhizomes down next to the soil surface before applying herbicides. If you see any green, then the plant is not completely dormant and could be damaged if it comes into contact with herbicides.  This commonly happens around sidewalks where radiant heat from the concrete keeps the turfgrass next to it warm enough to prevent dormancy.

For more information about lawn care, contact UGA Cooperative Extension in Coweta County at 770-254-2620 for more information. The University of Georgia College of Agricultural & Environmental Sciences is an equal opportunity, affirmative action organization.