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Do you know if this mildew is now systemic in the plant and if @Hanglow really needs to go so far as to totally destroy the whole plant as he is threatening?
Or is it only a temporary infection encouraged by this year's weather that can hopefully be eliminated by cutting back the bine and treating with a 'mildewicide"?
Yep - powdery mildew is primarily airborne so there's not much you can do to prevent new infections other than practising good hygiene and not letting old infected leaves over winter, and then treat with fungicides on an annual basis as required. Whereas verticilium is primarily soilborne so that's where you need to be paranoid about soil movements and disposing of old crowns. And downy overwinters primarily on plant material, both debris and in dormant buds, but can also be in the soil.
googling the various hop diseases doesn't seem to help an amateur like me much, a lot of the pictures of the cones are similar!
Once they've got to that stage, they all tend to look alike, it's like diagnosing a human death when the corpse is a month old. Diseases are most characteristic in the early stages, before all the secondary infections set in, and on the leaves rather than cones. But as I say, 90+% of the time if you've got a disease (as opposed to feeding damage) then it will be one of the big three of downy, powdery and verticilium, and they're reasonably distinctive if you look closely.