Can you drive a MOSFET directly from a microcontroller?
There are several reasons for using a gate resistor, like:

Damping ringing between wire inductance and gate capacitance;
Slowing down the switching transition and preventing spikes (will also help with EMC);
Reducing the gate drive current spike to a level the microcontroller can safely handle.

If any of these apply for your application, you must use a gate resistor, or another method.
On the other hand, if your application isn't critical re switching speed, there are no good reasons not to include a gate resistor other than component count; I would still add a small one (say 100Ω as Andy suggested) to prevent or reduce possible problems; it is the safe way of doing things.
At the low switching frequency you mention it will do no harm other than slowing the switching action a bit and very slightly increasing power dissipation in the MOSFET for the very short period during the switching transition.