I picked the last of my leeks today and when stripping the outer skins noticed red lines running down the length of the stem. I have seen it before but can't find out what it is doing it. Can anyone help or advise me please.
Alium leaf miner. Where the grubs eat the leek, a red stain appears. If you see little black grains, that's the pupating grubs. If you search on here, you'll find various posts from about 5 years ago. It seems to be less of a problem now, perhaps because the advice is to put barrier netting on the crops.
I think the number of people using barrier netting is reducing the pest pool... only found one grub in 48 plants last season.