How much damage can thrips do?

My plant has thrips and I can see the spotting on the leaves but how will these affect the plant?

They can kill a plant or stress it so bad you get no yeild. Kill em.

They can get pretty bad fast if you don't do anything about it. Their life cycle is complex you should google it to see what you're up against. Outside it's not too much of a problem 'cause you have help from other insects but indoors needs quick attention. They are tricky because they adapt and gain resistance to most insecticides very quickly. Something with spinosad is the best bet to kill them off fast. Thrips don't have much defense against it and it is organic. Azomax or some other neem based product is good also but there is a chance that they will become resistant to it quickly. It is very important to be thorough when you do whatever it is that your going to do. The more days that they are exposed to anything the more likely they are able to adapt.

Kill them!!!!! Like jessy said use Spinosad and take them out or you will regret it. I had a fight with them on my last batch and I can tell you it goes from "shit should I do something about this or will they make it the last couple weeks" to "Holy Shit Batman WTF happened to my plants" in a matter of days after you notice them. Personally I would hit them with Spino every other day for 3 applications making sure to get the bottom of your leaves. If you are more than say 2 weeks out from harvest I would hit them with a Neem solution on the 8th day. The Spino should kill them and the Neem should help ensure that anything missed doesn't reproduce.

Yep there nothing to f with get a pyrithreum bomb and nuke them