Grub Damage or Drought? How to Diagnose Brown Patches and Fix Them Fast

Grub Damage or Drought? How to Diagnose Brown Patches and Fix Them Fast

Brown patches can show up almost overnight—and on Long Island (Suffolk County), the cause is often one of two culprits: grub feeding or drought/heat stress. Treating the wrong problem wastes time and money, and in peak summer every day counts. Use this guide to quickly tell the difference, apply the right fix, and rebuild a thicker, greener lawn that’s ready for fall.

Why Brown Patches Appear in Suffolk County Lawns

Sandy and sandy-loam soils drain quickly, winds accelerate evaporation, and hot edges near pavement bake the root zone. In that stress, two things happen:

• Grubs (the larval stage of beetles) feed on roots just below the surface, cutting the plant off from water and nutrients.
• Drought/heat dries the upper soil profile; shallow-rooted turf wilts and turns straw-colored.

Because the symptoms can look similar from the sidewalk, you need a simple field diagnosis before you treat.

Fast Field Test #1: The “Carpet Roll” Check (Grubs)

Pick the edge of a brown area and tug gently upward like peeling back a corner of carpet.

• If it lifts easily and the roots are short or gone, you’re likely dealing with grub damage.
• If it resists and stays anchored, roots are holding—drought/heat is more likely.

While the turf is lifted, look for C-shaped, white grubs (¼–1 inch long) in the top 2–3 inches of soil. A few grubs are normal; higher counts (varies by turf type and density) correlate with damage potential.

Fast Field Test #2: Spade-and-Count (Grubs)

Cut a 1-square-foot flap 2–3 inches deep at the border of healthy/brown turf. Count the larvae you see.

• Multiple grubs per square foot + root loss = treat for grubs.
• No grubs, intact roots = look to irrigation, heat, or disease.

Fast Field Test #3: Screwdriver/Soil Probe (Moisture Stress)

Push a screwdriver or probe into the soil in both green and brown areas.

• Hard to penetrate in brown spots, easy in green = dry soil and likely drought stress.
• Evenly moist in both but brown persists = investigate disease, compaction, or prior grub activity.

How Grub Damage Progresses (Long Island Timeline)

• Late spring to early summer: Adult beetles emerge and lay eggs.
• Mid–late summer: Eggs hatch; young grubs feed aggressively on roots.
• Late summer/early fall: Damage appears as brown, spongy patches; wildlife (skunks, raccoons, crows) may dig.
• Fall/winter: Grubs move deeper; turf may not recover without reseeding.
• Spring: Surviving grubs feed briefly before pupating; damaged areas green up poorly.

If you see fresh digging, easy roll-up turf, and visible larvae, act quickly.

How Drought/Heat Stress Shows Up

• Uniform straw color on sunny slopes and pavement edges
• Footprints and mower tracks linger (turf doesn’t spring back)
• Soil is hot and hard in brown areas; green areas are cooler/moist
• After a deep watering or a thunderstorm, color improves within 24–72 hours

Unlike grub patches, drought-stressed turf typically doesn’t peel up; the roots are present but dehydrated.

Fixing Grub Damage (Step by Step)

1) Treat the Active Grubs

If your inspection confirms grubs, apply a curative grub control labeled for in-season activity and water it in per label to reach the root zone. Curatives work best on younger larvae; for advanced, late-season stages, you may need follow-up.

Tip: Preventative treatments applied earlier in the season are the best value; schedule them for next year to avoid repeat damage.

2) Stabilize and Rebuild Roots

• Light topdressing with compost or enriched soil improves moisture retention and microbial activity.
• Apply a balanced or starter fertilizer (phosphorus per local rules) to encourage root regrowth.
• Core aeration in late summer/early fall relieves compaction and improves oxygen/water infiltration.

3) Reseed Thin/Bare Areas

Overseed immediately after aeration with region-matched seed (turf-type tall fescue + elite bluegrass). Seed into the cores for better take, then follow a germination-first watering schedule (short, frequent mists; then taper deeper).

4) Protect Against Wildlife Digging

Where animals are foraging, consider temporary netting or repellents until grubs are controlled and new turf establishes.

Fixing Drought/Heat Stress (Step by Step)

1) Reset Irrigation for Depth

• Target 1–1.5 inches of water per week in growing season, delivered in 1–2 deep morning cycles.
• Use the tuna-can test (or cups) to measure actual output; adjust runtimes to reach your target.
• Break long cycles into two passes to prevent runoff on compacted or sloped areas.

2) Raise the Mowing Height

Set the mower to 3.5–4 inches for cool-season turf. Taller blades shade the soil, cut evaporation, and boost root depth. Keep blades sharp to reduce stress.

3) Relieve Compaction and Improve Soil

• Core aeration opens channels for air and water.
• Topdressing (¼") with screened compost increases organic matter and moisture-holding capacity—especially useful on sandy South Shore soils.

4) Address Hot Spots and Edges

Edges along asphalt, stone, and concrete heat up faster and dry first. During fall overseeding, boost seed rates at edges and consider a bit of additional topdressing for moisture retention.

Not Sure Which It Is? Use This Quick Decision Tree

Does turf peel up easily?
→ Yes: Likely grubs → Apply curative + water-in → Topdress + reseed → Schedule preventative next year.
→ No: Likely drought/heat → Deep morning irrigation → Raise mowing height → Aerate/topdress → Overseed in fall.

Still unsure after checks?
Pull a soil flap and inspect for grubs. If counts are low and roots are intact, treat it like moisture stress first—then reassess after a week of deep watering.

Prevention Plan for Suffolk County Lawns

Grub Prevention

• Schedule a preventative application timed to Long Island beetle cycles.
• Maintain dense turf with aeration and overseeding—adult beetles prefer thin, stressed lawns for egg-laying.

Drought/Heat Prevention

• Keep mowing at 3.5–4 inches; never remove more than ⅓ of the blade.
• Water early mornings, deep and infrequent, measuring output.
• Soil test every 1–2 years; correct pH with lime (when recommended) so fertilizer works efficiently.
• Use slow-release nutrition to promote steady growth and stress tolerance.

When to Bring in a Pro

Call a pro if:

• You’ve had repeat grub outbreaks or wildlife digging.
• Brown patches return each summer despite watering changes.
• You need help with soil testing, pH correction, calibrated aeration equipment, or seed selection.

A professional program coordinates preventatives, curatives, soil work, and reseeding so you get results quickly—without guesswork or wasted inputs.