Dry Spots After Double Fertilizing: Grubs or Watering?

Diagnosing Post-Fertilizer Brown Spots

Michigan lawn, double fertilizer application → expanding brown spots (10+ in). Over-fertilization possible, but if not re-fertilized, look deeper.

Top Suspect: Grubs

• Dig at green-brown edge; look for C-shaped white larvae.
• >1–2/sq ft → Apply GrubEx (chlorantraniliprole) now.
• Reseed dead areas after treatment.

Root Cause: Shallow Watering

• Daily 10–20 min = shallow roots → heat scald.
• New seed needs frequent/shallow; established grass needs deep/infrequent.
• Transition schedule:
  • Weeks 1–2: 10 min daily.
  • Weeks 3–4: 20 min every 2 days.
  • Weeks 5–6: 45 min twice/week.
  • Week 7+: 2 hrs once/week.
• Deep roots = heat/drought tolerance.

Best Practices Summary

• Mow high (2.5–3.5 in), frequent, recycle clippings.
• Fertilize: late spring, early fall, late fall. Never summer.
• Water deep/infrequent (except new seed).
• Annual grub check (July–Aug).

Bottom Line

Double fertilizing likely didn't cause spreading spots. Check grubs first. Then fix watering—shallow daily cycles are the silent killer of Midwest lawns.