Diagnosing Light Green Patches: Yellow Patch vs. Necrotic Ring Spot

Two Likely Culprits

Yellow Patch (Rhizoctonia cerealis)

• Appears in early fall with cool temps.
• Triggered by hard, compacted soil and poor drainage.
• Leaf blades show small purplish discolorations at tips, spreading downward.
• Black fungal strands between leaves.

Necrotic Ring Spot (Leptosphaeria korrae)

• Similar rings, but more distinct "frog-eye" pattern (green center, dead ring).
• Also favored by compaction and excess moisture.

Cultural Control (No Fungicides Needed)

• Water deeply, infrequently: Once weekly for 1 hour vs. daily 20 min. Early morning only.
• Improve drainage: Correct standing water areas.
• Core aerate in fall: Relieves compaction.
• Fertilize properly: Late spring (May), Sept, Oct. Avoid heavy spring N; no summer N.

Alternative: Weedy Grass Invasion

Rough bluegrass (Poa trivialis) forms light green patches that brown early in summer. Check leaf texture and seasonal behavior.

Key Insight

Both diseases are symptoms of poor soil conditions. Fix the environment (drainage, compaction, watering, fertility timing) and the grass recovers. Fungicides are temporary band-aids.