Identify a key sign of lawn fungus disease.

A key sign of lawn fungus disease is the presence of circular patches of turf with yellowing or dead grass. This characteristic symptom, often referred to as "fairy rings" or other patch diseases, helps distinguish fungal infections from other issues. The circular patterns are a result of the fungus growing out from a central point and can create distinct areas of affected turf, leading to noticeable contrasts between healthy and unhealthy grass.

Recognizing these circular patches allows for more accurate diagnosis and targeted management strategies. In contrast, while yellowing of grass leaves can indicate various turf problems, including nutrient deficiencies or drought stress, it is not specific enough to pinpoint a fungal disease. Similarly, uneven grass height could arise from numerous factors, such as inconsistent mowing or water distribution, and does not directly indicate a fungus. The presence of insects might suggest pest problems but would not be a reliable indicator of a fungal issue. Overall, the distinctive circular patches are a clear and defining trait of lawn fungus diseases.