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I just noticed this hard crusty black stuff at the base of plants today. What is it? It looks like it's eating the base of my plants. What should I do?
That looks like damping off to me. How far along are you? My buddy has had the same issue from scraping his cuttings for more roots. Sometimes the affected plants make it until harvest and snap like a chopstick when bent. Other times they just die in the trellis.
I made him quit exposing the cambium layer and the problem stopped. It only affected blue moonshine.
No, leave it be. You will just weaken it further. Look into damping off and the many remedies here. I would start with h2o2 treatments.
I see your in rock wool croutons. How often and how much do you water?
Once it got that far on my bros shit, it seemed nothing helped.
Post this up in the infirmary section. You will get plenty of answers there. If it is in veg if you can up your plant numbers, I would clone it, replace each plant with 25 lil ones and flower em.
Yeah agree with the stem rot diagnosis. Looks like the rockwool cube is staying wet so long that the stem can't dry out properly which can help lead to the rot. Can you maybe take a couple more pictures to give a better look?
The simple solution is typically to just lower watering frequency. Every third day instead of every other day, etc. If your room humidity is too high/air stagnant it will definitely make this even worse as the cube will stay moist for much longer after watering, meaning the stem is basically always wet.
Definitely damping off or stem rot as Wendull C and others have said. It is not that common in an established plant and mostly effects seedlings. It can be caused by numerous different fungi but in this case it looks like botrytis or grey mould. Unless it can be stopped asap it will probably kill the plant via destruction of the vascular tissues.