Where this disease prevails it is quite destructive. However, its range and frequency are not sufficient to render it of an alarming nature. Quinces affected with Bitter Rot show symptoms very similar to those exhibited by the apple, on which fruit this disease is so common in warmer states. Affected portions on the quince turn brown, the surface becomes depressed, and there appear the characteristic pinkish dots over the lesion. The name implies that the rotten flesh has a bitter taste; however, this is not a constant character. On this account, the name Ripe Rot has been suggested as a substitute. But the rot is not entirely a disease of ripe fruits, hence riperot is fully as objectionable. Usage demands that the name Bitter Rot be employed. Quinces grown in close proximity to apples affected with Bitter Rot may be expected to succumb. However, if history is a reliable basis for prediction, the disease may never be expected to assume destructive proportions. (See Apple, page 14.)

Reference

Halsted, B. D. Some fungous diseases of the quince fruit. The ripe rot of quinces. New Jersey Agr. Exp. Sta. Bul. 91: 11 - 12. 1892.