Hey buddy. Unfortunately you've been hit with white powdery mildew. And yes, it can destroy a crop as it eats sugars and can have/cause multiple problem. How it happens. Poor ven in a warm high RH envoir. With little ven spores land on your and in and around your plant. Is your intake fan turned on to pump air into the tent or have u got it set up to extract air? It's defo mildew. I'll try find something that can help u and DM it 2 u.