Guignardia citricarpa is a fungal pathogen primarily affecting citrus plants, particularly citrus fruits like oranges and lemons. It is responsible for a disease known as citrus black spot, which causes dark lesions on the fruit's surface, leading to reduced quality and marketability. This fungus thrives in warm, humid environments and can spread through infected plant debris or contaminated equipment. Effective management strategies include proper sanitation, the use of resistant varieties, and fungicide applications to minimize its impact on citrus production.