If they were over watered they might have a bad/weak root system can u look?
U may have an abundance of calcium or salts in ur water, what's ur waters PH stand point? It's a great indicater if ur feeding with a PH of 6.5 and its run off is 6.1 tells a lot!
Most bugs won't cause that type of damage but if they're stressing the plants they won't have great immune systems so weak against all manner of issues.
I'm surprised no ones mentioned broad mites yet!? =$