Summer patch

Symptoms. Symptoms of summer patch appear very similar to necrotic ring spot. This makes it very difficult to identify; if correct diagnosis is critical contact a local cooperative extension program or a qualified commercial lab. Although it is difficult to identify alone, if one takes into account grass species and cultural practices a trained eye can diagnose summer patch. Summer patch will appear as irregular patches, rings (less than 10 inches in diameter), and crescents. The "frog eye" appearance is often from the Poa annua being killed by the fungus while the middle living grass is Bentgrass. On lower cut turf, typically lower than 1.4 inches, summer patch is much easier to identify. A tug test can be performed and look for blackened roots. Yellowing and decline is often found on Poa annua in a mixed bentgrass area.
Disease Cycle. Summer patch is usually caused by an interaction of environmental factors (stress) and a root or crown rot caused by Magnaporthe poae. The fungus Magnaporthe poae is consistently found in grass roots but does not become noticeable until conditions are favorable. Favorable conditions include extended periods of humid weather and daytime high temperatures usually (greater than 82 F) in midsummer. Other causes include: poor air circulation, high soil moisture (sometimes caused by frequent irrigation), soil compaction (heavy traffic), and poor drainage. The disease does not appear noticeable during the cool weather of spring and fall. Summer patch seems to favor soil with a pH higher than 6.