Put some of the infected leaves in an envelope. There may be people who might pay quite a bit to infect their out-of-control mints.

I know, right? MINT IS SUPPOSED TO BE UNSTOPPABLE! And yet I managed to somehow acquire the one thing that's going to wipe mine out in a mere two weeks. What the heck?!!!

This post was edited by leggs on Wed, Jun 11, 14 at 11:17

Either too dry or too wet.

Some sort of a powdery mildew?

Back off on the watering, and don't water by spraying it.

Thanks! Will it eventually recover from the overwatering on its own or do I need to give it some kind of treatment?

I'm trying to work out what substance it's growing in. What is the gloopy looking blob in front of the plant?

Although it looks a bit sad it is definitely not dying as there are new shoots appearing away from the main clump.

The only 'treatment' for overwatering is to stop watering and let it the soil dry out a bit.

To me the soil looks very poor. Hard, dry (I see no signs of overwatering here), rocky, and concrete-like. Mixing in plenty of compost would help immensely.

Rodney

The soil's not great, but it's been doing fine in it for several months. As floral_uk pointed out, it's been putting out shoots like crazy.

Suddenly, though, they're ALL going gray at the bottom. It started with just one plant and quickly spread to all of them. Is it a pretty safe bet that it's just a watering problem or could a fungus have gotten in somehow? It doesn't look like bug-work to me.

Knowing mint's strength, I would go ahead and cut whatever is still good for eating, then cut the remaining from the ground level. Toss those and let the plant regrow.

Whatever problem it is, may kill the current growth and then allow your remaining stems to grow more.

Or alternatively, you can take any good branches of the mint and start them in a pot(s), until this problem is resolved. You'll still get your mint and not have it die or be all eaten up, and hopefully the problem will pass.

To me it looks stressed from drying out. Mint likes soil that is a wee bit on the damp side. If it goes dry for too long the plant starts to stress, and the first thing to go is the bottom leaves.

Also a water soluble fertilizer treatment might help it a bit too. Also when watering keep the plant dry, and water the soil not the plant. Also dirt splashing up on the leaves can cause what you are seeing. Last year my wife nearly killed of an orange mint plant with the sprinkler by first over watering, and letting the soil stay of the leaves, and then letting it go too long before watering it again. My solution this year is a soaker hose, and mulch. I have to keep the mint contained it is going crazy this year.