noun
1. : a disease of leeks especially in Britain caused by a fungus ( Phytophthora porri ) and characterized by yellowing and dieback of the leaf tips which finally turn white
2. : any of several diseases of cereal grasses (as maize) and other crop plants caused by mineral deficiencies and resembling fungous white tip in symptoms
3. : a disease of rice caused by a nematode ( Aphelenchoides oryzae ) and characterized by whitening of the leaf tips