mysticepipedon said:

I don't think that's leaf septoria.

This doesn't look like an immobile nutrient deficiency symptom, because the growing points are not affected, and the new leaves aren't affected, just the mature ones below the very tops. it kind of makes me think it's light-related, but I'm not sure.

Could you post pics of a larger area of the grow? I know it would be tough to impossible to get a pic of an entire plant, with the net and all.

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mysticepipedon said:

I don't know if it's this problem for sure, but many plants want more cal/mag in early flower. LED lighting seems to increase that demand.

In my grows it was often the leaves just below the tops that suffered, so that's why I kind of think it's cal/mag and light related.

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HaveApuff said:

This does look like a mag deficiency, and as I see you are already going into auto-flower, as a rule the plant still wants magnesium, but not so much calcium as it does in veg. Switching to a sulfur/mag in flower helps in keeping the mag in your supplements that are needed by the plant, while the sulfur encourages ripening

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How to fix Cannabis Magnesium Deficiency (Mg) Pics & Symptoms

Does your cannabis plant have yellowing lower leaves between the veins? See pictures of a magnesium deficiency and learn the easy solution.

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