Yes, a main disconnect is needed in the detached garage.NEC 225.31 requires a disconnecting means to be installed at the detached building. This is so you can de-energize the entire building in an emergency or for service.Since you are using a MLO (main lug only) panel, you will need to install a separate disconnect switch (breaker or fused) ahead of the panel. This disconnect must be readily accessible to occupants of the detached structure.Think of it this way: the MLO panel is just a junction box with breakers. It has no way to shut off power to the entire garage. Flag for review