Summer Patch

Magnaporthiopsis poae (syn. Magnaporthe poae)

Cool-Season Grasses Severe Fungus

Symptoms

Circular to irregular patches of wilted, straw-colored turf in summer. Patch margins often have a "frog-eye" pattern with a green center of less-susceptible grasses. Roots and crowns are dark brown to black.

Circular patches from 6 inches to 3+ feet in diameter, bleached tan to straw-colored
"Frog-eye" pattern: ring of dead turf surrounding surviving grass in the center of the patch
Roots and crowns are dark brown to black and severely rotted
Symptoms appear suddenly during summer heat stress — infection actually occurred weeks earlier
Turf in affected patches is unable to recover without fungicide intervention or re-establishment

Signs

Dark brown to black ectotrophic runner hyphae visible on roots and crowns under a hand lens — similar in appearance to take-all root rot
Perithecia (flask-shaped sexual fruiting bodies) may be found in thatch and at the soil surface, but are rarely observed in the field
Infected roots are dark and rotted; no sporulating structures visible without magnification

Biology

M. poae infects roots and crowns in spring when soil temperatures reach 65°F. Infection progresses through the root system without visible symptoms. When summer heat arrives, the compromised root system fails and patches suddenly appear. The pathogen overwinters in infected plant debris.

Favorable Conditions

Temperature range: Soil temps 65–80°F during infection; symptoms at 85°F+

Soil temperatures reaching 65°F or above (infection begins)
Hot, dry summer conditions following infection (symptom expression)
Compacted soils with poor drainage
Low mowing heights and mechanical stress
Acidic soils below pH 6.0
Thatch accumulation

Cultural Practices

Raise mowing height — closely mowed bluegrass is most susceptible
Core aerate to reduce compaction and improve drainage
Avoid drought stress — the interaction between root damage and heat/drought causes symptom expression
Adjust soil pH to 6.0–7.0; avoid highly acidic soils
Use nitrogen programs that sustain summer root growth
Overseed with resistant perennial ryegrass or improved bluegrass cultivars

Related Reports

No published reports yet for this disease.

Reports will appear here as they are peer-reviewed and published.