Baking powder for mildew issue?

My courgette plants seem to have a mildew or fungal issue.
I’ve researched apparently using baking powder solution seems to be a non chemical solution.

Has anyone tried this? Is it effective?

That leaf looks healthy enough! Some courgettes have a silvering in the leaf colour I think Yorkie is correct.

The other possibility could be damage from the seriously sunny and dry weather we have had. Perhaps make sure you have provided enough moisture for the plant as they don’t like a lack of water.