Sphaceloma fawcettii var. scabiosa
Also called lemon verrucosis, this fungal disease causes raised roughened warty lesions to form on the outside of the fruit. Although the inside of the fruit is unaffected, the disease should be controlled because it gradually reduces the vigour of the tree. Damp, cool weather encourages the disease.
Rough patches also appear on the stems and leaves, and fruit drop often occurs.