I have 4 pictures showing damage to the leaves of my dwarf mandarin tree. Please help!

Last picture:

My first thought for the yellowing leaves is a nutrient deficiency. Looking at the pictures on this page http://lemoncitrustree.com/store/pest-disease it seems to most closely match an iron or zinc shortage. (the bottom two images)

The brown spots made me think immediately of spider mites, but it also closely resembles one of the fungal diseases on this same page.

If I were dealing with this tree I would first give it a good dose of an organic fertilizer (a thick layer of compost might suffice).
If only a few leaves are affected by the spotting, I would remove them before the issue could spread. (this would be the same whether insects or fungus) If you have any good local nurseries, bring a sample of the leaves for the employees to look at. They should be familiar with the common ailments in your area. Even if they don't offer an organic solution, just knowing for sure what you are dealing with can make it easier to do more complete research.

Often just improving the nutrition of a plant will give it the fortitude to fight of diseases or pests on it's own. Citrus are one of those plants that can recover from extreme defoliation.

The yellowing might be too much water or too little nitrogen. Citrus are nitrogen pigs. Are you giving it nitrogen? Try peeing all around it about 3 times daily for a month or two -- or some other nitrogen source. See if that picks things up a bit.

If it's getting too much water, let the soil dry out a bit between watering.

But the brown spots and the brown on the base of the leaf . . . that's a new one for me. Has your weather been wet and cold? When it's cold, I really cut way back on water.

Thank you both! I will give it extra fertilizer and nitrogen. (I'm not very good at keeping up with those.)

I will try taking the leaves to a local nursery, too.

The lows have been in the high 40s or low 50s lately. It might be getting too much water lately, but I think a nutrient deficiency is more likely.

We're both in California. We were promised El Nino, but never really got it in Southern Cal. From what I understand, you got a lot of rain up your way this past winter. It may just be waterlogged. Does your soil drain well? Is it sitting in a low, cold pocket? Between the cold and he water, that might be the issue.

As things warm up, you'll need to give it water, but things are so cool and wet right now --- I would imagine that the poor thing is half drowning. Give it some nitrogen and let the roots dry out. See if new growth begins to flush out as the weather warms up. All my citrus has already bloomed and set fruit, and new growth is coming on like gangbusters.

It certainly doesn't look like it's in any mortal danger. It should be fine once the weather warms up.