I have a fungus infestation
 

I have a fungus infestation from the high humidity in my grow room. How do I treat the fungus, which is white, circular, about four inches across. some of it has moved to a low stem. Do I have to remove the plant from the room? It is one of my biggest and best and i am reluctant to do so. Do I have to buy some type of systemic fungus treatment??

Yes if it is only on that plant because it will spread to all your plants if you don't get control of it right away. Add fans to your room. Get that air moving 24 hours a day to control fungi. Keep infected leaves trimmed off to keep it from spreading. Keep your room clean even the floor. No carpet or dirt floors. Put down plastic or better yet white tarp to reflect the light back up. Or go buy some fungicide and start treating.