Ligustrum are very prone to three leaf spot diseases, all of which are caused by fungal organisms. Exosporium concentricum, Cercospora adusta, Phyllosticta ovalifolii are commonly observed on these plants in the fall, though can appear at any time. Spraying with a fungicide now (something containing Daconil), cleaning up all the fallen leaves and putting down new mulch will be helpful. It is likely that you will have to spray these plants from now on, but conservative fertilization practices can help subdue which ever of the diseases it is. (No more fertilizer for the rest of the year.) Keep your plants well watered, but never over watered in times of drought.

By the way, any of these diseases are considered cosmetic and not necessarily fatal, but serious infestations can lead to the ultimate and permanent decline of your shrubs. All of the above fungi are ubiquitous and did not necessarily come WITH the plants, but have been able to take hold because of the stress of transplanting. You can help the plants overcome the problem.