disease of pear trees in autumn. damage fruit tree. sick leaf of fungal infection gymnosporangium sabinae. rust spot on

pear rust fall spot autumn sick disease gymnosporangium damage sabinae fungal nature tree leaf fruit leaves fungicide phytopathology unhealthy grow closeup diseased danger aeciospores rusty infestation summer fungi parasite fungus pathology gardening green infected yellow prevention orange foliage treatment pathogen plant pest environment agriculture farming