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I presume you started with new soil and using good water with quality nutrients. Possibly the start of a fungus in the roots. Let the top of the soil dry well between waterings. Tip the plant out of the pot gently and get a look at the roots ball and see if they are white or brown. If you post a photo of the whole plant it would be helpful for the best answer.
Could also be the natural progression of a plant big enough to have completely shaded those leaves. Without seeing the whole plant, there's no way to know.
Could also be the natural progression of a plant big enough to have completely shaded those leaves. Without seeing the whole plant, there's no way to know.
I'm guessing this is outdoor. If that's the case it's fine considering the time of year for the reasons GMT stated. As the plants enter flowering and use up their nitrogen the lower leaves will naturally turn yellow and lose vigor. As the leaves die they'll lose their resistance to disease, some of the necrosis does looks fungal. I wouldn't worry about it or start spraying unless it spreads to healthy parts of the plant that get plenty of light.
Earlier in the year I had a similar necrotic pattern on my leaves outdoors, on a few of the lower shaded leaves. Only the plants were in Veg and much younger. I know the culprit, slugs. I took pictures to document the damage even though the plants were healthy. I love my plants, make sure they have good soil, water, and light, or else it could have turned into a disease. Here's some of the pictures.
You can see it's fungal, probably boytritis, that grew after the slug chewed on it. Probably infected by the slug. Most people wouldn't have noticed, I was trying to document the diseases the slugs spread so I investigated and took pictures. This is what the whole leaves looked like, at the macro level you hardly notice it.
The plants were and are perfectly healthy. I didn't spray or freak out. Stuff like this is part of nature.