DaisyI said:
Those look like the oldest leaves. They have served their purpose and continue to yellow until they drop off (or you cut them off) the plant. As long as you have new leaves, all is good.
BigBill said:I am alarmed to see this "damage" and I do not like it!
At first I was thinking insect damage on the underside of the leaf eventually making itself visible on the upper surface of the leaf.
BUT in your last image of the underside of a leaf, between the 2 spikes or inflorescences, those irregular yellowish markings look like it could be a virus! And if it is, that is bad because there is no cure for it.
We have no information as to the light, the temperature and watering details but I am concerned all the same.
BigBill said:I think that your growing conditions are fine.
Any insect damage I can think of does not look like what your images show. Same for fungal or bacterial issues. Hence my concern. It could be insect damage from the underside of the leaves but then those yellow kind of circular/oval stuff I see does not look like insect damage. At least not that I can recall in all my 45 years.
It is not heat stress or cold stress plus your temperatures are fine.
DaisyI said:Are the yellow spots on the old leaves only? If it was a virus, wouldn't the entire plant be affected, including flowers?
DaisyI said:Are the yellow spots on the old leaves only? If it was a virus, wouldn't the entire plant be affected, including flowers? Isolate it and see what develops, if anything. Use your sanitary practices (but you should use those as a matter of course).
If it is a virus, its not in the potting medium but in the plant tissue. Virus are spread by vectors in an exchange of bodily fluids - the same way we get viruses. That could be an insect but most likely a human. Wear disposable gloves and sterilize surfaces and tools between cuts and plants. A 10% bleach solution will kill the virus too, but it sure plays havic with your gardening tools.