Diagnosing Brown Patches: Grubs vs. Fungus vs. Drainage

Front lawn brown patches April-June (possible grubs/leatherjackets). Back lawn new patches in August. Need diagnosis and solution.

Term Clarification

"Leatherjackets" = crane fly larvae (European crane fly). Feed on roots in spring. Grubs = beetle larvae (Japanese beetle, June bug). Feed summer/fall.

Differential Diagnosis

Symptom	Grubs	Brown Patch Fungus	Crane Fly
Timing	Aug-Oct damage	Hot, humid weather	Apr-Jun damage
Pattern	Irregular, rolls up	Circular, "smoke ring"	Thinning, not distinct patches
Root test	Tugs loose, grubs visible	Roots intact, lesions on blades	Roots clipped at crown
Soil	Often well-drained	Wet, compacted, high N	Wet, organic soils

Diagnostic Steps

1. Cut 1 ft² flap in transition zone (healthy to damaged). Count grubs (>5-10/ft² = treat)
2. Check blades for fungal lesions (brown margins, tan centers)
3. Soil probe: compaction, moisture, thatch depth
4. Send sample to extension lab if uncertain

Treatment by Cause

Grubs

• Preventive: Chlorantraniliprole (Acelepryn) in June
• Curative: Trichlorfon (Dylox) in Aug-Sept
• Organic: Beneficial nematodes (Heterorhabditis), milky spore (Japanese beetle only)

Brown Patch

• Fungicide: Azoxystrobin, propiconazole
• Cultural: Reduce N, improve drainage, morning water, reduce thatch
• Organic: Baking soda spray (1 tbsp/gal) - preventive only

Crane Fly

• Monitor: Spring larval counts
• Treat: Same as grubs if threshold exceeded
• Birds often provide natural control

Organic Ecosystem Approach

Build soil life: compost, reduced chemicals, diverse plantings. Predators (birds, beetles, nematodes) suppress pests naturally. Transition takes 2-3 years but yields resilient lawn.

Identify first, treat specifically. Blanket applications waste money and harm beneficials.