Eureka lemon brown spots inside

My Eureka lemon is finally producing fruit, but most of the lemons are brown and shriveled inside. It’s always been on one side of the lemon, never across the entirety of the inside. Anyone recognize this?

Not sure but I wish someone who did would please reply. I have been wondering the same.

Check the UC guide to Citrus pests and diseases.

Without seeing the rind or especially knowing a bit more about the conditions the tree was fruiting in, it’s difficult to tell, there are quite a few diseases or ailments that can impact the formation and quality of citrus fruit. I think where OP is in zone 10a it’s probably safe to say it was not cold damage, and so I’ll offer my guess that it could be from irregular irrigation while the fruit was maturing, or a boron deficiency

As @Richard mentioned, a great place to start is to check symptoms Vs. a good reference like UC’s IPM guide for citrus.

Anecdotally, I’ve seen superficial damage like OP’s before on citrus fruits that were carried through a cold winter with lots of temperature fluctuations - some of the sides of the fruit in my greenhouse that were exposed to the worst of the cold weather looked a little bit like that, but the rinds were obviously damaged from the cold as well.

There are also some insects that can pierce through the rind and introduce infections or vascular deformations, and in my opinion on immature fruit sometimes it is really difficult to notice this damage until after the fruit has formed a bit more completely, or you cut it open and see a “bad” spot inside after harvest. If it just looks dry inside and not like some kind of rotten or infected material from a bug or pathogen entry (sometimes thorns can cause a good entryway for pathogens on citrus), and you’ve ruled out other common diseases or ailments on the list, then it might just have been exposed to suboptimal temperatures during flowering and fruit production, or irregular watering, or maybe both.

Please keep in mind that my growing conditions in 6B (and consequently, a lot of the problems I’ve faced in growing potted and in-ground citrus here) may be very different - I’m sure what I’ve said may not apply to everyone, they are just my observations so far.