HOW TO IDENTIFY IT
Rust looks like tiny little reddish-brown bumps on the underside of the leaves. It looks like the plant has a rash! The top of the leaves will get yellow splotches on them. At first it will just be a few spots but soon, if it’s not treated, it will spread over the whole plant as well as any other mint plants in the garden.
THE DAMAGE IT CAUSES
Mint that has been infected with rust cannot be eaten. Eventually the leaves will die and drop off and the plant will become stunted. The problem with rust is that, inside each of the bumps are thousands of little spores which burst out and blow in the wind to other mint plants in the garden so they need to be checked for rust too.
HOW TO CONTROL IT
The best way to treat rust on mint is to cut it off but there is a trick to it. To start with, get a big plastic bag because the leaves and stems can’t be put into the compost because the spores will survive and spread through the garden. Instead, seal them in the bag and throw in the bin.
To cut off the rust, don’t just take off the leaves, cut off the whole plant! It sounds brutal but because it is mint, it will grow back beautifully but don’t do this with any other plant as you might just kill it. Use secateurs to cut all the stems off at soil level, putting everything into the plastic bag. When you’ve finished, scrape up any dead leaves that are on the top of the pot as these will have rust on them as well.
Finally, cover the top of the soil with fresh potting mix or compost to completely cover the plant. It will look like the pot is empty. Then, water the mint with liquid fertiliser. Within a few weeks, new shoots will start to pop up and soon the plant will be back in mint condition!