What’s Causing Brown Patches in My Lawn This Fall?

Brown patches in Florida lawns are a common concern during late summer and fall. Homeowners may notice thinning turf, yellowing grass, or expanding areas of decline and immediately assume insects are to blame. However, brown patches can be caused by a variety of issues, including insect pests, fungal diseases, improper irrigation, nutrient problems, and environmental stress. Correctly identifying the cause is the first step toward effective management.

Brown Patches in Florida Lawns Caused by Insects

Several insects remain active during late summer and early fall and can cause significant turfgrass damage if populations become high.

Fall Armyworms

Fall armyworms are caterpillars that feed on turfgrass leaves and can cause rapid damage during late summer and fall. They chew grass blades, creating ragged patches and thinning turf. Homeowners may notice increased bird activity as birds feed on the caterpillars. Healthy lawns often recover once feeding pressure declines.

Chinch Bugs

Southern chinch bugs are among the most damaging pests of St. Augustinegrass in Florida. These insects feed by extracting juices from grass plants, causing yellowing and browning that is often mistaken for drought stress.

Common symptoms include:

• Yellow or brown patches in sunny areas
• Damage beginning in hot, dry locations
• Expanding areas of declining turf
• St. Augustinegrass that appears drought-stressed despite adequate moisture
• Small black-and-white adults or orange-red nymphs near the border between healthy and damaged grass

Because chinch bug damage resembles several other lawn problems, close inspection is often necessary to confirm their presence. Chinch bug infestations are most common in stressed turf.

Tropical Sod Webworms

Tropical sod webworm caterpillars feed on grass blades, creating a thin, ragged appearance throughout the lawn.

Common signs include:

• Notched grass blades
• Small brown patches
• Green frass (insect droppings)
• Small moths flying from the lawn when disturbed

Damage typically becomes more noticeable during warm months when caterpillar populations increase.

Brown Patches in Florida Lawns Caused by Disease

Not all turf damage is caused by insects. Several fungal diseases become active during periods of high humidity, excessive moisture, or seasonal temperature changes.

Take-All Root Rot

Take-all root rot is one of the most serious diseases affecting St. Augustine grass in Florida. Unlike insects that feed on leaves, this disease attacks the root system, reducing the turf’s ability to absorb water and nutrients.

Symptoms may include:

• Thinning grass
• Yellowing areas that gradually enlarge
• Weak root systems
• Turf that pulls up easily from the soil

Because these symptoms often resemble drought stress or insect damage, examining roots and stolons more closely may be necessary. In some cases, dark fungal growth can be observed on infected plant tissue, helping distinguish the disease from insect-related problems.

Large Patch

Large patch disease becomes more common as temperatures begin cooling in the fall.

Symptoms include:

• Circular brown patches
• Orange or yellow borders around active patches
• Expanding areas of affected turf during cooler weather

This disease is most often observed in St. Augustine grass and zoysia grass and can be particularly noticeable in poorly drained areas.

Dollar Spot

Dollar spot produces small, straw-colored spots scattered throughout the lawn. As the disease progresses, these spots may merge into larger areas of damaged turf.

Homeowners may notice:

• Small circular patches approximately the size of a silver dollar
• Bleached-looking grass blades
• Increased symptoms in lawns with low fertility

Although usually less dramatic than large patch or take-all root rot, dollar spot can still affect lawn appearance and vigor.

Before You Treat

Because many causes produce similar symptoms, diagnosing brown patches in Florida lawns often requires a closer inspection of the grass blades, roots, and surrounding growing conditions.

Brown patches may result from:

• Insect feeding
• Fungal diseases
• Drought stress
• Overwatering
• Soil compaction
• Improper fertilization

Applying an insecticide to a disease problem or a fungicide to an insect problem wastes both time and money while allowing the actual issue to worsen.

If possible:

• Inspect grass blades closely.
• Check for insects near damaged areas.
• Evaluate irrigation coverage.
• Examine roots for signs of decline.
• Contact your local UF/IFAS Extension office for assistance with diagnosis.

Prevention Starts with Healthy Turf

Many causes of brown patches in Florida lawns can be reduced through proper lawn care practices:

• Mow at the recommended height for your grass species.
• Water deeply but only when needed.
• Avoid excessive nitrogen applications.
• Improve drainage where water collects.
• Reduce lawn stress through Florida-Friendly Landscaping™ practices.
• Monitor regularly for early signs of pests and disease.

Whether the cause is chinch bugs, armyworms, sod webworms, take-all root rot, large patch, or dollar spot, identifying the source of brown patches in Florida lawns can help homeowners select the most effective management strategy and maintain a healthier, more resilient lawn throughout the year.