It sounds like Downy mildew to me monsterhitz. Downy mildew is much whiter and thicker/heavier than Pm and downy mildew is harmless really.
When you see the white, almost opaque appearance of Pm in the field, the fungus is in its final stages and is "flowering" so to speak. The opaque whiteness are spores being released. By the time you see white with pm, the plant is very sick and has numerous yellow leaves. The disease has been in the plant for several weeks and is systemic in nature. Powdery mildew is incurable. It is easily preventable but practically impossible to cure once contracted.. The chemical in Eagle 20 or Immunox will control the disease hopefully to the extent that it doesnt hurt the plant to badly, (not always)but it will still have the disease until the weather turns cool enough that the fungus dies.
I wouldnt use Eagle 20. Its far far too strong a concentration of chemical to apply to cannabis and even though when smoked you cant feel the effects of it, its in the plant tissue. Immunox is the same chemical but in a far safer dosage for cannabis and kills pm on contact. Its sold in many home improvement and garden stores as Spectracide Immunox all purpose fungicide. Its perscribed for vegetables and is in a dosage thats safe. Eagle 20 is for commercial applications and is not safe for cannabis. You will be smoking the chemical if you use Eagle 20. You just wont know it..
But as i say, youre describing Downy mildew. If the plants arent also sick, its Downy. Google and read about it.