Summer in the Southeast is the season when lawns either thrive or collapse depending on what you do in May and June. St. Augustine and Bermuda grass — the two dominant lawn species across the region — are warm-season grasses that love heat, but summer in Atlanta, Houston, and Miami throws problems at them that demand specific attention.
If you see irregular yellow or dead patches expanding outward from the sunniest areas of your lawn — particularly along pavement or south-facing slopes where heat is most intense — suspect chinch bugs before anything else.
Chinch bugs are small (1/5 inch), black and white insects that feed by piercing grass blades and injecting a toxin that disrupts water movement through the plant. The grass yellows, then turns brown, then dies. According to University of Florida IFAS Extension, chinch bug populations can reach 20 to 30 insects per square foot before visible damage becomes apparent, meaning infestations are often well established before homeowners notice the first yellow patch.
To confirm: part the grass at the edge of a yellowing patch and look at the soil surface. Adult chinch bugs are visible to the naked eye. Alternatively, push a metal can with both ends removed into the soil at the edge of a damaged area, fill with water, and watch for small insects floating to the surface within 5 minutes.
Treatment requires a pyrethroid insecticide (bifenthrin, lambda-cyhalothrin) applied to the entire affected area plus a 3-foot buffer. Water it in lightly and don't irrigate heavily for 24 hours.
Large patch — the warm-season version of brown patch — is the primary fungal disease affecting St. Augustine and Zoysia in the Southeast. Unlike the version that affects cool-season grasses, Large Patch can kill the crown of the plant rather than just the blades, leading to permanently bare areas.
The conditions that trigger it: warm nights above 70°F, high humidity, wet foliage from evening irrigation, and excess nitrogen fertilization. The symptom is circular patches of yellowing then browning grass, often with a distinct orange halo at the margin in early stages. As NC State TurfFiles documents for Large Patch disease, the pathogen Rhizoctonia solani is most active when soil temperatures fall between 70°F and 85°F — which describes most Southeast summers from June through September.
The most important preventative step is switching all irrigation to early morning. The most common mistake is applying a nitrogen-heavy fertilizer in late summer, which pushes lush growth that's highly susceptible. Stop fertilizing with nitrogen after August 1st across most of the Southeast.
Gray leaf spot is a summer disease specific to St. Augustine — you won't see it on Bermuda or Zoysia. It appears as small gray or tan lesions with dark borders on individual blades, and in severe cases the lawn looks scorched. It's most active in hot, humid, wet weather during July and August.
The conditions that increase susceptibility: recently applied nitrogen fertilizer, frequent light irrigation, cloudy weather. St. Augustine lawns that receive too much nitrogen in summer are dramatically more susceptible.
Treatment with fungicide is possible but rarely necessary if you reduce nitrogen input and improve irrigation timing. The disease is self-limiting once summer temperatures moderate.
Every warm-season grass in the Southeast has a mowing height that keeps it healthy through summer. Mowing too low stresses the plant and removes the leaf canopy that shades the soil (reducing weed germination and retaining moisture).
Never remove more than 1/3 of the blade in a single mowing. Removing more than that stresses the plant and causes yellowing. If you've let it grow too long, mow it down gradually over several sessions rather than scalping it in one pass.
The conventional wisdom is to stop fertilizing warm-season grasses 6-8 weeks before the first expected frost. In Atlanta, that means no nitrogen after mid-September. In Houston and Miami, the window is longer — light applications are fine through October.
More importantly for summer specifically: don't over-fertilize in July and August. High nitrogen in peak summer pushes soft, fast-growing tissue that's maximally susceptible to chinch bugs and fungal disease. University of Georgia Extension's turfgrass fertility guidelines recommend keeping total summer nitrogen applications below 1 lb of actual nitrogen per 1,000 sq ft per month, and skipping applications entirely during drought stress or disease pressure. If your lawn is healthy and dark green in July, skip the fertilizer application.
If you're unsure whether to fertilize in midsummer, take it as a signal to run a soil test first. Excess potassium and phosphorus accumulate in Southeast soils over time; a soil test from your state extension service costs under $20 and tells you exactly what your lawn needs — and what it doesn't.
Chinch bugs, Large Patch, gray leaf spot, and drought stress can all look similar from a distance. Upload a photo for an accurate diagnosis.
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