Edges of marrow leaves turning white

[ladykathryn]

What could be the cause of this. I have never seen this happen before. these are young plants that are being grown by a friend of mine and she asked me to contact you regarding this. She only planted her well established sprouts a week ago. They are covered by a warming blanket that lets in light and water. Could this be not allowing light to come in properly.

She waters ever other day. And has not used fertiliser on her young plants. Other plants that she is growing in her green house are green and doing very well, just like the other ones. She is not sure if she should plant her new babies out with the others if this might be a disease.

This is not a powered residue, or spots. It's just on the edges all around the leaves where they should be green. Can anyone help, she is really concerned. Like me this is her first go at a veggie garden and wants to make sure everything is okay.

Thank you very kindly everyone.

[the.fee.fairy]

sounds to me like a lack of light. are they leggy too?
Leaves need decent sunlight to make their leaves green (the chlorophyll needs the light to photosynthesise) so if there's not enough light, then they're wont to turn white. There are some veg that people deprive of light to turn white (i'm thinking asparagus here, but i'm not sure).

[ladykathryn]

the plants are out doors, and in full sun, there are no trees nearby. Maybe the warming blanket is the problem?? What do you think?

[NZAmish]

Sounds like Powdery Mildew to me.
My plants had the same probelm this year.