Symptoms of disease refer to what?

Symptoms of disease specifically refer to the observable plant responses that occur when a pathogen infects a plant. These responses manifest in various ways, such as wilted leaves, stunted growth, discoloration, or abnormal growth patterns. Each symptom provides vital clues about the underlying issues affecting the plant, including the identity of the pathogen involved and the severity of the infection.

This understanding is crucial for effective pest control and management practices, as recognizing the symptoms enables farmers and pest control advisers to diagnose the disease accurately and implement appropriate control measures. The other options do not capture this concept accurately. Defects in agricultural equipment relate to machinery performance rather than plant pathology. External conditions impacting growth could influence plant health but do not represent the symptoms of a disease caused by pathogens. Lastly, while observations made by farmers are important for identifying symptoms, they do not define what symptoms are. Thus, identifying symptoms as plant responses to pathogen infection is essential in the field of plant pathology.