Is this Mold in my Garage
I agree with Bill - It is unfortunate that the plywood was hung so low, especially since you have a concrete block supporting the framing. It at least is is better than the sill sitting on the slab.
You could just let it stay as long as you can stand it and it is functioning. Eventually, you can expect some mold and serious rotting in the future.
As a fix, remove the plywood and search for a more suitable material and hang it higher. If you are lucky, you will have 8" high block and not just 4" high.