An even better picture would be helpful, still not 100% clear on diagnosis......do you see eggs or black specs under the leaves too?
If it was me, and assuming your still in veg- go buy Forbid 4F on Ebay. They sell little bottles for around $20. You only need to mix between .5ml and 1.2ml per gallon. Keep the pH between 5.5 and 6.5. Spray the shit out of everything- plants, pots, floor, walls, etc. I typically shut my room down an 1/2 hour early to let the plants cool down a bit. Make sure you do a thorough watering a few hours before you spray the plants. Turn the lights down very low or off before spraying and after spraying, turn all fans and lights off and let the room dry out slowly over night. Spray plants top to bottom well.
If you still see any activity in a week or two, I'd switch off to another product i.e. neem, mighty wash, green clean, monteray spray, liquid ladybug, Avid, or one of the other 100 available products. Do not switch to flowering until the issue is resolved.