If the yellow leaf were coming from the rhizome and was watery, I would suspect a fungal infection. Since it seems to be located in the middle of the leaf and the lesion seems to be dry, I think the plant is just absorbing nutrients back and sacrificing that leaf.
I think Cattleyas are very resilient, especially unifolates. I've had a rootless Cattleya purchased from a terrible vendor in the midst of winter survive 9 months without roots, and then shoot a new growth. Yours is making a speedy recovery.
Not sure if your plant is underwatered or rootless. Either way, it's dehydrated. If it doesn't have roots except for the new ones growing, I would hold off on the fertilizer. Without roots to absorb it, it'll just accumulate in the medium. I would've potted in a smaller pot (always pick pot size based on the size of the root ball, not the upper plant), but your media is chunky and I think the plant will do fine. I would just water the heck out of it with very clean water and fertilize sparingly or not fertilize at all until next Spring. However, keeping the media moist at all times should be helpful, especially those new roots currently growing will want to stay really moist.
As a note for when you can start fertilizing again: I have experimented with giving my Cattleyas a summer rest this season and they've responded shooting new growths and making me happy. Overall, I think even 100 ppm N a week is "up there" in terms of fertilizer, 50-75 ppm N a week has given me better results in the long run. I would recommend reducing fertilizing by A LOT in weather extremes (summer and winter) and fertilize more in fall, and much more in spring. Plants grow slower but excess fertilizer favors rots in my experience.
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Last edited by MateoinLosAngeles; 08-21-2023 at 08:24 AM..
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