[viettaclark]

My crops suffer badly from this every year and although I know now not to water the leaves because it creates the conditions it loves, I still get it.
I think some could be because I plant quite closely in my raised beds and there isn't enough air circulation. The garden is also fairly sheltered.
Now I'm wondering if I'm doing it myself by composting mildewy material? My compost gets very hot due to chicken waste, I don't use it for 2 years and I've not noticed any correlation between outbreaks of mildew and use of compost. I didn't put compost on the sugarsnaps and they're the worst. Courgettes, chard, spinach and cucumbers are affected and I expect the perpetual strawbs will get it (along with grey mould) seeing as they're beginning to fruit again now......
Any wise thoughts on why my plants are so susceptible? It's impossible to control!

[JayG]

Mildew would be only one of probably hundreds of different fungi present in unsterilised compost so I doubt it's that.

It's often a problem as the season progresses because many plants are reaching the end of their life-cycle (getting "ready to rot"!) and the days get progressively cooler, shorter and more humid.

Creating a micro-climate which makes the humidity worse is obviously a bad idea, especially in an already sheltered garden. You are obviously aware of all this; be vigilant about removing old and mildewed leaves which will in itself improve the air circulation and don't leave finished crops in place for the same reason.

[emptydraw]

If it becomes a persistent problem, why not try mildew resistant varieties. Our "Tosca" Courgettes are extremely healthy, right next to my outdoor gherkins which are coverded in mildew.
So it does pay to spend some time and pick your varieties carefully.

[mumofstig]

They're also more likely to suffer when the weather is hot and roots are dry.
Keeping the roots well watered helps 

[Kleftiwallah]

"It is said" .  .  .  .that if you collect mare'stails, bruise it then boil it up in water , strain and then mix with a smidge of soft soap (or Lux flakes), this will keep the powdery mildew at bay.  I don't know if it will reverse an attack but,  you never know if you don't try.     Cheers,     Tony.