What is a sign of petroleum injury in turfgrass?

A sign of petroleum injury in turfgrass is the presence of irregular patches of dead turf. This phenomenon occurs due to the toxic effects of petroleum products, which can disrupt the plant's ability to take up water and nutrients, leading to localized areas of death in the grass. The irregularity of the patches is significant because it indicates that the petroleum exposure was not uniform, impacting certain areas more than others based on factors like soil composition, drainage, and the way the petroleum was applied or spilled.

In contrast, the other options do not indicate petroleum injury. Patches of green grass could suggest areas of healthier turf that are not affected, while uniform ground cover would imply that the entire area is growing uniformly and healthily. Deep soil moisture is unrelated to petroleum injury, as it more commonly relates to adequate water availability for the grass, which is beneficial for growth rather than a sign of damage.