Cucumbers

Our cucumbers seem to have developed a kind of powdery mildew. Is there anything we can spray them with to fix this or is it terminal?

I haven't tried it, but apparently milk spray helps . probably diluted. The Google machine should have the answers.

"Is there anything we can spray them with to fix this or is it terminal?"

Yes and no.

Most fungicides eg copper sprays, Bravo or Saprol will help minimise powdery mildew and help prevent it - so yes, you should probably spray. However there is no magic cure. Spray won't fully fix an established powdery mildew problem. they may not even make a dent in a well established problem.

Fungicides are usually most effective as a preventative i.e. Spray before the issue occurs or at worst at very first sign of it. In your situation where is has become obvious on some leaves (I assume), it is possibly best to remove the worst infected leaves (they'll probably die anyway) and spray the remainder.

I could be wrong here - and someone will correct me if I am. But I think sprays like Bravo or Saprol will be a little better at fighting powdery mildew than a copper spray is, however copper sprays are generally considered to be more 'organic' and less a horrible chemical than the other two - if you're worried about that sort of thing.

Nods head agreeing!
I have this problem with my Toms as well as the cucumbers, but the plants all live on and still fruiting. I have sprayed them with a diluted vertion of anti fungi and insect repellant [bugs under leafs of toms]].

You can try a milk spray with bicarb in it plus a bit of detergent to help it "stick". I can't remember the proportions but you can google it. It's most effective BEFORE the midlew starts though, so if you remove the worst affected leaves and start spraying now, the new growing leaves should have some protection.
Best to start spraying before any signs of mildew, and you have to spray every single week.

Try a solution of apple cider vinegar and water - 3 tablespoons of ACV to 2 litres water. spray under and over leaves.

Copper - Natures Way has a copper/sulfer mix. It's organic too.
However you should spray every 2 weeks to prevent it, once it has it, that's pretty much it. it won't affect the vege. just make the leaves look awful.
And spray over winter too, the spores overwinter in the dirt and branches (on other plants).