High this is caused through high humidity – Powdery mildew – white spot and will spread very quickly so treatment must be carried out as soon as possible – I use a mixture of baking powder – One table spoon to One gallon of water – Spray top and bottom of leaves – up to three days if necessary. This has worked for me in the past- Triffid Killer -- I meant Baking Soda not powder

If it really is powdery mildew, the most effective treatment is actually 1 part milk to 9 parts water - must be cow's milk though, and spray till run off. Here's something to read about milk treatment and mildew - note the comments about the smell, but if you use totally skimmed milk, its less smelly - its the cream that makes it smelly. The article also says there's some 'confusion' about the ratio of milk to water - there isn't really, its 1:9 for powdery mildew, 1:2 for blackspot, and inbetween those two treatments is where the so called 'confusion' arises. In both cases, its cows milk, not soya or almond or coconut or sheeps or goats!

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