Does your lawn look like something from the movie “Signs” with Mel Gibson?  Big circles of grass that is dying back?  You are not alone, but fortunately this is just a fungus and not aliens!

Large patch is a common disease of warm season turfgrass, especially St. Augustine and Zoysia grass in Texas.   It is caused by the fungus Rhizoctonia solani.  This fungus is present in the soil and thatch layer all year long, but it thrives in cooler temperatures when the soil is wet.  We got a cool front and rain a couple weeks ago, and many lawns started showing symptoms of large patch shortly after that.

The first symptoms of large patch are circular patches in the lawn with orange or yellow borders.  These are almost perfectly shaped circles, and then it spreads out from there.  The large patch fungus infects the grass’s sheaths, stolons, and roots.  The diseased shoots pull out easily from the sheath.   In fact, an easy and practical way to diagnose large patch is to see if you can easily pull the grass blade out of the sheath.

Large patch infection occurs in areas that are over-fertilized late in the fall, have poor drainage, get too much water, and have excessive thatch.  Good management of your lawn can help prevent the environmental conditions that make it easy for large patch to establish.

Proper fertilization plays a big role in preventing large patch.  The last time to fertilize in the fall is six weeks before the first frost.  Fertilize the first time in the spring about three weeks after green-up.

Try to improve drainage in areas that hold water for long periods of time.  Remember that you can probably turn off your automatic sprinkler system until late spring since we have more rain and cooler temperatures now.  Just water in the fall if we have extended dry periods.

Core aeration and vertical mowing will decrease thatch and discourage disease.  Using the proper mowing height will also help.  Mow at two to three inches for St. Augustine and one to two inches for Zoysia.

If you do have large patch, fall is the recommended time to apply a fungicide.  Try to apply fungicide before or immediately after the disease begins in the fall.  Spring fungicide applications are not recommended because warmer spring/summer temperatures will limit the spread of large patch.  You can find many options for fungicides labeled for controlling large patch at local nurseries.