Last year as I maintained a commercial facility under contract the mature crabs all wilted upon warm -hot weather. Lost leaves and one of our Lesco reps claimed it was apple scab,treat early next year with dormant oil on lower main limbs and trunk. With "spring" here buds are appearing and after discussing the symptoms with another contractor he thought it was cedar rust, and couldn`t remember what they had used. Then if diseased I`ll have to treat the canopy? Hoping to nip it in the bud this year so they look good.