Thank you flor answer me. Im in argentina. Both are being grown in pots and mixed outdoors and inside because of the coming of the winter. The orégano Is just a few and i think the problem could be a miner worm. The mint is widespread and i dont know what it could be.

I can't say what it is, but can you take it to a local Ag Extension/University?

Otherwise:

You could cut the mint back... a lot, and let it grow all new leaves. (Mint is notoriously hard to kill.)

I'd cut off any problem branch from the Oregano and watch for any more signs of this problem.

How cold does it get, Franco? Both stay outside all year round here.

Around 0° C. They are both young plants so i kept them inside in the night.

Both can cope with 0c. Oregano is evergreen but mint mostly dies to the ground in winter but will reappear in spring.. If you want mint all year round it need protection but it’s harder to keep healthy indoors. If you have a cool, light place like a glass porch or greenhouse it would be better than in a heated house.

So should I cut down the mint to the ground? And wait for the spring?

Don’t cut it down until it dies of its own accord.

Ok Thank