08/07 - Begining of the vegetation phase.
13/07 - Had to travel for an emergency for 3 days! When back home the leaves were yellowing. Began with NPK 20-20-20 3,5g per liter.
15/07 - New leafs growing green and healthy.
- Lights at 30% the entire week.
Only on one leaf of one plant. Is this some fungus or virus?
It looks a bit like coffee rust, but I couldn't find anything else like it.
How should I proceed?
Thanks in advance!
Pretty certain this is Leaf Spot Fungus otherwise known as Rust Fungus... and you'll need to jump on this quickly as it spreads fast... it spreads by spores that you can't even see so don't think you've got any time to waste here... I won't go into all the details of what you need to do as this article is very thorough.. Do give it a read and get going so you don't lose your entire grow...
https://www.urbanorganicyield.com/rust-spots-on-leaves-during-flowering/
Good luck!