Blister spot is a bacterial disease causing damage to apples. Not all cultivars have shown susceptibility in commercial fields – the most susceptible is Mutsu (Crispin), followed by Fuji, Red Delicious, Golden Delicious, Cortland, and Rome Beauty. Blister spot first appears in mid to late July as small raised blisters. The blisters increase in size and turn a purplish-black as the season progresses, and can range in size from 1 mm to 5 mm. Up to 100 blister spots can appear on one fruit.