Grubs, Disease & Fungus: How to Fix the Real Problem

Grubs, Disease & Fungus: How to Fix the Real Problem Don’t guess — identify first, then treat

Brown patches, thinning turf, and spongy spots can come from grubs, disease, drought, dog urine, or poor soil. Treating the wrong problem wastes money and can make the lawn worse. The most important step is confirming what you’re actually dealing with.

Grubs — white C-shaped larvae under the sod

Grubs are the larval stage of beetles. They live in the soil and feed on grass roots. Heavy populations can kill patches of turf that pull up like a loose carpet.

How to confirm

• Look for irregular brown patches that don’t recover with water

• Grab the edge of a patch — if the sod lifts easily and roots are chewed, grubs are likely

• Dig a 1-foot square about 2–3 inches deep and count the white, C-shaped larvae

• Rough rule of thumb: more than about 5–10 per square foot often justifies treatment (thresholds vary)

• Increased digging by birds, raccoons, or skunks can be a clue

Timing and treatment Preventive products target young grubs before they cause heavy damage. Curative products are used when grubs are already large and feeding. Many products need to be watered into the soil to reach the root zone — follow the label. Healthy, well-rooted turf tolerates low grub numbers better than thin, stressed lawns. Grubs, Disease & Fungus: How to Fix the Real Problem

Grubs, Disease & Fungus: How to Fix the Real Problem

Lawn disease and fungus

Fungal diseases thrive when grass is stressed and conditions favor the pathogen — often a mix of moisture, temperature, and weak turf. Common patterns in cool-season lawns include leaf spots, melting-out, dollar spot, rust, and snow mold.

Clues it’s disease rather than drought or grubs

• Patches that appear during or after wet, humid periods

• Lesions, spots, or a smoky/gray cast on the leaf blades

• Rings or distinct patch shapes that expand outward

• Sod that does not lift easily (roots still intact)

Cultural controls come first Most home-lawn disease pressure drops when growing conditions improve:

• Water early morning so blades dry during the day

• Mow at the correct height with a sharp blade — never scalp

• Reduce thatch and relieve compaction so air and water move properly

• Avoid excess nitrogen in hot or wet periods

• Improve airflow and sunlight where possible

Fungicides can help protect high-value turf or stop a spreading outbreak, but they work best alongside better cultural practices — not as a substitute for fixing moisture and mowing problems.

Quick comparison

Sign	More likely grubs	More likely disease
Sod lifts easily	Yes — roots chewed	Usually no
White C-shaped larvae in soil	Yes	No
Leaf spots / lesions	No	Often yes
Appears after long wet period	Less typical	Common
Birds/skunks digging	Often	Less common

Prevention beats treatment

Thick, properly watered, well-mowed turf resists both grubs and disease better than thin, stressed grass:

• Maintain steady growth with appropriate fertility

• Water deeply and infrequently

• Mow high enough for your grass type (often 3–3.5" for Kentucky bluegrass)

• Aerate annually and overseed thin areas

• Clean up excessive leaves and debris that hold moisture

What to do this week

1. Inspect damaged areas — lift a small section and dig a sample square

2. Count grubs if present; note leaf symptoms if the sod stays rooted

3. Fix obvious stress: watering schedule, mowing height, thatch, compaction

4. Choose a product only after you know the target

5. Follow the label exactly — rate, watering-in, and re-entry for kids and pets

Identify first. Improve conditions. Treat only what you confirm.