bitter rot
nounDefinition of bitter rot
1
: a very destructive disease of apples, grapes, and other fruit caused by a fungus (Glomerella cingulata) and producing cankers on the twigs, limbs, and fruit spurs and a spotting or blistering and decay of the fruit characterized by bitterness of the pulp
— called also anthracnose, ripe rot
2
: a rot of ripening grapes caused by an imperfect fungus (Melanconium fuligineum)