Every spring it produces lovely blooms, then the leaves soon turn yellow, develop black spots, wither and die. Also, there is a gray, hard, scale over much of the trunk and branches. An arborist treated for three years with anti-fungal plugs with only modest results. We have not continued the treatment for the last two years. Can you offer any advice to save this tree? Thank you.

I suspect the crab apple is susceptible to a fungal foliar disease called Apple Scab. Infection takes place as leaf buds just begin to expand very early in the Spring. Several treatments are needed per label instructions. If the first applications are missed, there is little that can be done. Fungicides are only preventive in nature. Sprays applied later may provide protection from futher infestation, yet any leaf impacted will fall to the ground. Cleaning up the fallen leaves in the fall will reduce overwintering inoculum. the blue gray blotches are lichen moss. they do not harm the tree, just an iindication of age and enviornmental conditions.