What is your circulation fan situation like? You really need air blowing through every nook and cranny above and below the canopy. I would spray those ASAP with potassium bicarbonate or Greencure, which is the same thing but with a wetting agent. There are other things you can do to knock it back long enough to harvest usually, but if the plants are young it's going to be a long battle. Once you have it, you will need to be extra vigilant from now on with every single grow-start treating weekly with biofungicides, neem/silica, aspirin, and the potassium bicarb. Some people burn sulfur with good effects too.
