This is leek rust, same sort of thing as onion rust or garlic rust. It’s a fungus that spreads itself via airborne spores. It wont kill the host plant, but it will severely affect it’s growth.
I’ve had a bit of this each year, mainly on the leeks and garlic, but it’s much worse this year. I’m going to be planting my garlic soon, and I’m concerned that it won’t come to much if it succumbs to rust from the onset. There’s not a lot I can do unfortunately. The usual crop rotation methods are recommended, along with good hygiene, i.e. clearing affected leaves from the bed and not putting them in the compost where the disease will remain.
So I have cut away the worst affected leaves – it’s too widespread to remove every bit – and going against my usual organic methods, I have sprayed them with a fungicide. Not ideal, but I want to try and clear the disease as best as possible before I plant out my garlic and onions.
Once we get some very cold weather, frost in other words, then it should kill off the disease. But obviously the plants will have already suffered a set back by then, so I’m holding off planting my garlic just yet, and I’m hoping I can at least alleviate the worst of the condition on the leeks. Fingers crossed.