Mildew or summat

[Martin H]

I planted some discounted onion sets last month to give me a supply of "spring onions" through the autumn. But today they are well infested with some disease. Is it mildew, the first stages of allium rust, or something else? Is there anything that can be done to clean them up and make them appetizing?

My first thought was mildew simply because the nearby sweet peas have suddenly got it, see pics.

[Two_Sheds]

diseases don't usually pass between different species.

Your sweet peas have powdery mildew, very common in dry weather


Your onions are out of focus, so it's hard to say, but they can get many problems, not all of them a problem.

Some Common Onion Pests and Diseases | GrowingYourOwnVeg