Q What is mint rust?
A The most obvious sign of attack occurs at the beginning of summer when new shoots are thickened and distorted. They become covered with tiny cup-shaped blobs called cluster cups or aeciums. These release aeciospores, spores that drift on the breeze to infect new plants. Where they land and cause a new infection, yellow pustules form, which release the summer spores called uredospores. These are highly infectious, spreading the disease very efficiently.
Sometimes plants are seriously attacked, losing leaves and even dying. By the autumn, the pustules turn darker as they switch to teliospore production. These spores get washed into the soil, where they end up in the underground buds of next year’s mint crop. They germinate in the spring and infect young foliage,
causing the cluster cups that start the cycle once again.
Caption: Mint rust is highly infectious
Q Which plants are affected by mint rust?
A The fungus can survive the winter inside common mint, but not other hosts. Common mint and peppermint are very susceptible. Some other mints, and sometimes other plants, such as marjoram and savory, are affected.
Q What can I do if mint rust occurs?
A Good hygiene is the first step. Remove and destroy any infected plant material by burning, or consign it to the dustbin. Affected mint beds can be burnt off with a flame gun to get rid of as much contaminated material as possible. There’s no need to buy a flame gun for small areas or single uses, as equipment shops hire them out. Alternatively start again with fresh plants in a new part of the garden.