Which symptoms are specific to individual plants or their parts?

The correct answer highlights that "plant symptoms" refer specifically to the responses or indicators of distress that are observable within individual plants or their parts. These symptoms can manifest as changes in color, shape, or texture and are crucial for diagnosing issues such as pests, diseases, or nutrient deficiencies affecting that particular plant. By focusing on plant-specific symptoms, a grower can accurately identify the problems plaguing individual specimens rather than general environmental factors affecting larger areas.

In contrast, the other choices pertain to broader concepts. "Stand symptoms" apply to the overall health and density of a group of plants rather than specific symptoms in individual ones. "Visible symptoms" usually refer to observable effects but lack the specificity tied to individual plants that "plant symptoms" maintain. “Environmental symptoms” encompass reactions to broader growing conditions, such as soil pH or moisture levels, rather than the unique characteristics of a specific plant's distress signals.