Leek rust is a fungal disease causing bright yellow spots on the leaves. It is often worse in long, wet spells.
Remedy: Mild attacks of rust won’t affect the plant, but serious infections may cause leaves to shrivel and affect yield. There is no control for rust once you have the infection. Make sure you don’t crowd plants, as this increases humidity and increases the likelihood of infection. Dispose of any badly affected plant material, and don’t grow garlic, leeks or onions in the same spot for three years.