Add powdered malted barley to a handful of compost and water it. Leave it in a container
After a few days it will have a lot of fungus growth
When it is visibly covered in fungus, place it in a ladies stocking. Create compost tea from it being sure to aerate it for 2 days using an air stone. Please see the sticky for more information on aeration
Then spray this fungal compost tea on the plants and the fungus in the tea will out compete any bad fungus