Turfmate field notes · Diseases

Summer patch

Magnaporthiopsis poae, formerly Magnaporthe poae.

Summer patch is a root disease of certain cool-season grasses. It becomes conspicuous in hot weather as weakened roots struggle to support the plant. Different grasses in a mixed surface may respond differently, leaving rings or uneven patches of damage among surviving turf.

Summer patch affecting annual bluegrass while neighbouring bentgrass remains green.
Summer patch affecting annual bluegrass while neighbouring bentgrass remains green.
Photo: Pete Dernoeden, Ph.D / Syngenta GreenCast · Full photo ↗

What to look for

  • Small areas of slow growth, thinning or wilt that turn yellow, bronze or straw-coloured.
  • Circular or irregular patches, sometimes with a surviving green centre and a more damaged outer edge.
  • Dark, declining roots or crowns beneath affected plants, especially where heat combines with drainage or compaction stress.

More photos to compare

Compare the overall pattern with the plant detail. Check the grass species and growing conditions as well as the appearance.

Summer patch in a fairway containing annual bluegrass and bentgrass.
Summer patch in a fairway containing annual bluegrass and bentgrass.
Photo: K. Happ / Syngenta GreenCast · Full photo ↗
Summer patch damage in Kentucky bluegrass.
Summer patch damage in Kentucky bluegrass.
Photo: Pete Dernoeden, Ph.D / Syngenta GreenCast · Full photo ↗

Check the grass and site

Australian guidance lists wintergrass, fescue and Kentucky bluegrass. Identify the affected species in mixed turf: the photographs include damaged annual bluegrass growing beside surviving bentgrass.

Confirm it before you treat it

Identify which grass species is failing and compare the roots with healthy turf nearby. A ring-shaped patch alone does not establish the cause. Record the weather and site pattern, and request a turf diagnosis if damage persists, expands or returns.

What to do next

  1. Review irrigation and drainage, avoiding a pattern of repeated light watering that leaves soil continually wet.
  2. Reduce stress by reviewing cutting height and traffic, particularly on already weak or scalped areas.
  3. Address compaction and support balanced nutrition through a planned recovery programme appropriate to the grass species.
Seasonal watch

Conditions matter more than dates.

Symptoms become more visible during summer heat, particularly where rainfall, poor drainage or compaction has stressed roots. Sunny, exposed areas and water-flow routes may be affected. The root problem can begin before obvious leaf damage appears.

Why is green grass left inside some damaged rings?

A less susceptible grass may survive or grow into the centre while another species declines. That mixed response is a useful clue, but it still needs to be considered with the host, roots and growing conditions.

Compare similar problems

Reviewed 18 October 2026 · Turfmate. Identification guidance is not a laboratory diagnosis or a spray calendar.

Technical sources & image credits

Syngenta photographs are reproduced in full with attribution. Source grass species and settings are identified where supplied; photographs support identification and do not replace diagnosis.

A Turfmate product link does not imply endorsement by a photographer or source.