Looks like leaf miners too me, certain of it. There are many different types of control. Pesticides, sticky traps, biological ect... Just google leaf miner control.
How bad is it.... If its isolated to just those leafs i would cut them. Then spray neem mixed with Dr.B or any soap spray. Maybe let a ladybug or two into your grow room.
I usually dont like spraying anything on my plants that far into flower. Good luck.
Leaf miners is a name used for a large variety of different bugs that live inside your leafs and pruduce larvae. Like I said before any insect soap with some neem should do the trick unless your whole garden/plant is infested.
It will if your plants are a few weeks into flower that's why i try to use it as a preventative spray while my plants are in veg. I use a 75-25 mix of dr. Bronner hemp peppermint soap and pure neem oil.