jz, the yellowing is more likely to be a overly wet issue and spots could be related (fungal) due to wet conditions. If you have not changed the soil for the trees and it is not draining freely enough. Perched water at the bottom of the pot will cause problems. As the soils break down they filter to the bottom of pot with watering an air spaces between particles in mix become absent.

Take off the yellowing/spotted leaves and throw in trash.

Rick