You are looking for a fairly decent sized bug there. See if you can see them in under the leaves. If you cannot find an insecticidal dormant oil like neem, just use soapy water in a spray bottle. But on a plant that size, just use your eyes, look for the bugs and kill them. Hopefully they are not soil born bugs.
A sterile grow space is the better thing to spend your time on. Keep the bugs out in the first place so that you do not have to pick up the pieces from an infestation at a later stage.