Is This Powdery Mildew?

[wax]

Hi everyone,
Its my first year growing Courgettes and I've noticed two of the plants have started developing a whiteness around the edge of the leaves, one leaf on each plant. I'm not sure what it is. It doesnt look like any of the pictures google throws up of powdery mildew but it could be the beginning of it.
Can anyone who knows about it take a look and see what they think?
I read that if it is powdery mildew then I just need to snip the infected leaves off. Is this OK considering they are the first true leaves on each plant?
Thanks!

[toomanytommytoes]

Could it be cold damage?

[wax]

Could it be cold damage?

It shouldn't be. They haven't been outside, just on the windowsill. As they have got larger I have left them on the windowsill behind the blinds at night where there is a bit of a draft but not much. Ive always left them there with smaller, weaker tomato seedlings and they seem fine.

[Snoop Puss]

Hi wax. If they're in a greenhouse and got splashed when you've been watering, the leaves could have got scorched.

Have you got a photo of the underside of the leaves?

Edited: sorry, didn't see your reply to toomanytommytoes before posting. Still think sun scorch most likely problem. In which case, don't cut the leaves off. Mildew is unlikely in an indoor environment, I think, in any event.

[nickdub]

Looks like a bit of sun scorch to me - most likely when we had that very sunny weekend.

[wax]

Here are some pics of the underside.

[Snoop Puss]

^Not mildew, I'd say.

[Derbydal]

it looks like some kind of leaf miner or caterpillar ! atb Dal.

[wax]

So would it be best to remove the leaves?

[nickdub]

Not if it is scorch - bit like sunburn, but in the case of a plant the burnt area is leaf tissue so as it grows it makes new leaves and the old ones become less important - I'd leave it alone, but possibly give a thought to how close to where the lights come in you are putting your seedlings - to be fair its rare to get bright sun light in April but it could happen again if we get strong sun this month.

[ameno]

Initially I thought sun scorch (my cucumber seedlings have a bit of that), but seeing that picture of the underside of the leaves, I'm thinking it might be overwatering.
Cucurbits respond to excess water by ejecting it through the pores along the leaf margins during the night. If you look at them at night, you may see droplets of water along the leaf margins. This can often cause the cells around the leaf margins to die, and produce those slightly translucent patches you can see on the undersides of the leaves. It happened to one of my cucumber plants last year.
Either way, it's nothing to be too concerned about. Maybe take a look at how much light and/or water they are getting, but otherwise just leave them be and they should still grow fine.

[wax]

I think I'll move it to the windowsill with net curtains between the plants and the window and see how it goes.

Thanks everyone for the help.