What are these black/brown patches on my corn plant

Question

I recently purchased a large dracaena fragrans, collquially "corn plant." Its stalk is approximately 1 meter tall. I keep it indoors, in front of a north facing window (probably not ideal, but at the moment I don't have any other room for it), although there is a white fence right outside the window which reflects good light. It's winter, although I'm in zone 10, and my apartment is ~17C (64F) most of the time.

Recently, I have noticed some of the leaves have large brownish/black patches (see attached photos). The patches are thinner feeling than the rest of the leaf and lack the slightly waxy texture of mature leaves.

Of note, when I purchased it, one of the stems was dried and dead and infested with what seemed to be mealy bugs or something similar. I immediately removed it, and I have not seen any bugs, though I have attached a picture of that area, and you can see black specks, which I suspect are dead bugs, but I'm not sure.

I did a cursory image search and didn't find anything that looked too close to what I am seeing, and I was wondering if anyone here could shed some light on this.

Answer 1

The general term for this is necrosis or cell death. For some reason the membrane that surrounds the cells ceases to function normally; this may have a knock-on effect on other neighbouring cells depending on position in the chain of command. It results in the cells losing moisture (turgidity) and appearing to reflect light differently as the leaf thins and leaves veins protruding. Depending on the leaf structure it may turn black and crackly and fall away completely, but in the case of this corn plant and other monocots there is sufficient structural strength in the leaf fibres that this may not happen until the entire leaf dies.

So now we just speculate on the why it happened. Recall that there is a stage in the life of a leaf when it is very fragile and susceptible to damage, whether mechanical (hit with an object) or vascular (fluid transmission). Simply rubbing between fingers may be enough to disrupt normal function - this is unlikely with this plant as we don't normally associate it with fragrant leaves, but that might explain damage to one side of a leaf, for example. Another possibility is that as the leaf was expanding it was restrained unnaturally and could not develop in the normal manner, leaving some areas deprived of normal sap flow to the extremities. Yet another reason is irregular watering; if the plant is forced to choose where to send resources then some parts may be cut out of normal flow.

But the situation looks good, you have some very nice buds coming on and now that it is in a stable environment (plants don't like change outside their normal parameters) over time you can get rid of the stressed parts and bring on the new growth.