<unk>  is a physiological plant disorder that affects some grape varieties such as Concord. It is essentially a potassium deficiency that causes the leaves on a vine to turn purple and eventually<unk>  as chlorophyll is lost. For wine growers this<unk>  of chlorophyll inhibits the vine's ability to transmit sugar to the grape, leaving the resulting grapes with a low brix count that may be less than ideal for wine making.
Black spot leaf disease
Ascochyta diseases of pea
Scabies
Black rot 
Demodicosis
Foot-and-mouth disease
Chancroid
Zoonosis