oh that's not good.
This is the link to the RHS site and it talks about protecting with fleece.
https://www.rhs.org.uk/advice/profile?pid=652

hope it helps.

Thought so. Makes it a bit expensive to grow them then by the time we have bought the fleece and the hoops.
Wonder how long one would have to not grow them for the moth to die out through lack of food.

yes it does a bit. Not sure really and I also think they like onions too. :o(

We no longer can grow onions, we have White rot which takes 30 years on non-growing Alliums to clear from the ground.

This has been a big problem for a number of years here and they say there is nothing on the market that will get rid of them