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Thank You both for your responses. These plants are outside in clackamas coots mix about 3 weeks into flower, the plants are extremely large for the amount of soil they are in. These are a friends plants who brought the leaves to my attention, my initial thoughts was nitrogen or zinc deficiency or a combination of the two.
Going to hit them with some kelp and neem soaked water a few times over the next week or two.
If it is the bottom and lower outer leaves, take a look at your canopy, are they shaded, crowded etc? You may have too many leaves and as you go towards the fall they are starting to die off naturally or not photosynthesizing, how does the entire plant look? If you have more of them mid canopy you may consider adding more N to get them through and get your yield. If it's magnesium that would be very likely 3 weeks into flower gobbling it all up with flower set, both are quite fixable, if you check out modern methods page he has a schedule for top dressing and teas for 10 weeks just to get an idea of what he is adding, he does a top dress at start of flower with ewc and meals to break down slowly through flower and get them through.