Large Patch in Zoysia, St. Augustine, and Centipede

NC State describes large patch as round patches from about a foot across to more than 3 feet. The symptoms are most obvious in cool, wet weather in the fall and in the spring. Plenty of lawns look fine in November and then green up with tan circles still sitting there, because the fungus was active before you could see it. On the leaf, look at the sheath, the part wrapped around the stem. Lesions there run tan, yellow, orange, or red. That orange or brown rim on the sheath is the close-up clue. From the street it just looks like a faded circle.

This disease used to be called brown patch. NC State changed the name because it is a different situation from brown patch on fescue: different time of year, different grasses, a different strain of the fungus Rhizoctonia solani, and a different control plan. Fescue and bluegrass are immune to large patch. The summer brown-patch problem on a tall fescue lawn is the other disease. If that is your lawn, start with fungus versus drought stress instead of this page.

Among warm-season grasses, NC State ranks centipede and seashore paspalum as the most susceptible, then zoysia, then St. Augustine. Bermuda is rarely hurt in a lasting way and usually grows out of it. A Bermuda lawn with summer brown spots is more often drought, grubs, or something else. Do not assume every circle is large patch.

NC State says large patch starts when soil temperature falls to about 70°F in the fall. The symptoms do not have to show up the same week. Cool, wet stretches in fall and spring are when you see the circles. The fungus is favored by too much nitrogen in fall and spring, poor drainage, overwatering, heavy thatch, and mowing too low.

That is why the same zoysia lawn gets a bigger circle every year in the low spot by the patio. The fungus is in that soil. Extra fall fertilizer and a sprinkler that runs because the timer says so are feeding it. The zoysia calendar holds nitrogen back from September through November for this reason. The St. Augustine calendar does the same after mid-September.

You are looking at circles in spring, at green-up. The useful fall spray already passed. NC State says fungicides have to be preventive. As the soil warms, the fungus slows down. A spring spray on the margin of an active patch can limit spread while temperatures are still bouncing around. It will not paint the dead center green. Map those circles, with a photo or a note, so next fall you can treat the spots instead of the whole yard. Hold nitrogen. NC State's cultural guidance is to skip nitrogen on warm-season grass within about 6 weeks of fall dormancy and within about 3 weeks after green-up starts. The grass is growing slowly and does not need a push. Mow at the height that grass wants. Zoysia and centipede that are scalped get this disease worse.

You are heading into fall and this lawn has a history. This is the spray that matters. NC State's large patch publication times it off soil temperature:

• St. Augustine and centipede: start when soil temperature has fallen to 80°F for 5 or more days in a row. In some years that is mid-August.
• Zoysia: start when soil temperature has fallen to 70°F for 5 or more days in a row.
• Two well-timed applications can cover the season on many lawns. Where the disease is severe, repeat every 4 to 6 weeks as long as fall soil stays above 50°F.

The St. Augustine maintenance calendar from the same university describes the fall program as starting at 80°F and continuing monthly until soil drops below 60°F, and it adds a spring application beginning when soil reaches 55°F for four days in a row. Use those as the same idea: fall prevention first, soil temperature instead of a month name, and a spring follow-up only if the lawn has a history and the soil says the fungus can still work. Watch it on the soil temperature tracker. A printed "spray in September" misses a warm fall and a cool August alike.

How you spray matters. NC State says to use at least 2 gallons of water per 1,000 square feet, because the fungus is on the leaf sheath and a mist on the leaf tips misses it. More water, or about 1/8 inch of irrigation afterward, helps. Several fungicides in their table are marked not for home lawns. Homeowner products that do list large patch often use active ingredients such as azoxystrobin, propiconazole, or myclobutanil. The rate and the interval are on the label of the bottle you bought. Do not borrow a golf-course rate.

Between applications, water only enough in fall and spring to keep the lawn from severe drought stress. Fix the soggy spot if you can. Aerate compacted areas when the grass can recover, not in the middle of a cool, wet outbreak.

• Calling every summer brown spot large patch. In July heat, check chinch bugs, grubs, and drought before you buy a fungicide.
• Feeding zoysia or St. Augustine in the fall to "help it recover." Fall nitrogen is one of the conditions NC State ties to this disease.
• Spraying dead grass in April and skipping the fall preventive the next year.
• Using a fungicide in a tiny amount of water so it never reaches the sheath.
• Mowing zoysia or centipede too short.
• Treating a tall fescue lawn for large patch in August. That summer disease is brown patch, and fescue does not get large patch.