Others here know more about citrus than I do, but that looks to be one of the worst cases of chlorosis I've ever seen. I almost always guess "overwatering" when I someone says the leaves are yellowing, but those leaves look starved for nitrogen to me. If you find that chlorosis is the main issue, I'd suggest:

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* double or triple the size of that circle that is grass-free;
* use a fast-acting, soluble nitrogen & iron fertilizer around the base and the newly-cleared area;
* put down blood meal or another slower nitrogen source and pile compost over the cleared area (but not around the base);
* spray again with potassium-based insecticidal soap, which is non-toxic but more effective than dish soap. It kills on contact, so you can hose the whole tree down an hour later and wash it mostly free of residue. Look for any ant colonies and consider ways to keep them out of your tree (Bait, traps, tanglefoot, spray, ...).

Your tree is very old, which is not a benefit, but dicot is correct in the belief it is suffering from starvation. The green moss on the old limbs is seasonal and will go away by itself. I do not see any signs of insect damage. You will need to buy citrus labeled fertilizer, which should list all the minors that citrus requires. I would extend the the cleared area out at least to the drip line. Then with a rake add the amount of fertilizer suggested on the bag and just rake it in, do not dig it in. Cover the soil with a vegetative mulch or compost leaving about 6 inches around the trunk bare. The fertilizer is going to suggest applying it 2 or 3 times a year, but in your case I would add it monthly and hopefully you will see some new growth on your tree. The mulch is very important to help the soil overcome its compacted condition and so be sure to keep it on year around. I would also start a regular watering regimen probable once a week in the dry season. With new growth you may attract aphids or scale noticeable by black honey dew or ants. They are easily controlled on citrus with ultra fine horticultural oil. Post again next year so we can see how your tree is doing. Al

Thanks dicot and calistorga, I'm going to take your advice and see if I can't nurse this one back to health. I will report back!

You want to get some LIQUID Ironrite; mix it with water to proportions listed on label snd drench ALL the soil around the tree to a foot past the drip line. I mean really put a lot down.... you tree needs immediate rescue. Then do as directed by those gardeners above.

Also, it wouldn't hurt to put a little Miracle-Gro in the water as well.

Ironrite has toxic things in it. Look it up on the web. But, you can use miracle grow with iron or lily miller makes an iron in a shaker can, or there is omsocote with iron, that is called omsocote plus. Also compost is good to put around the tree to improve the soil health over all in the long term.

I just wanted to add this link. Lead is harmful to children if they play in the soil. I agree with the last poster. If the soil is in bad shape that is why the tree won't absorb the iron, so you have to fix the soil up with compost and organic matter.

Here is a link that might be useful: Ironrite thread ca gardening

If you will use the fertilizer formulated for citrus, it already contains the iron, zinc and other minors citrus requires, as well as the correct ratio of NPK favored for growing citrus. Al

Dying tangerine trees.
I have 2 tangerine trees in Santa Barbara,Ca.It seems to me that they are both dying.I have tried more water, I have tried less water,I have tried Phosphate spray for root rot.I have tried mulch all to no avail.
The two trees right now are loaded with fruit, but no leaves and no new growth.I read somewhere that trees have lots of fruit just before they die.Is there some way to save these trees? I tried to include photos but couldn't
trees are almost completely without leaves. but lots and lots of fruit.I thank you all for any help I can get.
trees are about 30 years old.
pedroza

Citrus requires regular feeding with a high nitrogen fertilizer, such as those labeled "citrus and avocado". You don't say anything about your soil, which is probably seriously compacted and poorly drained. Yellow falling leaves is usually a sign of starvation. You don't mention aphids or scale so presume they are not visible. I would scratch in citrus fertilizer as directed out at least to the drip line. water it in and cover bare soil with three inches of compost or mulch. Pick much of the fruit(the oldest is probably no good anyway)and get the load off the tree. Al

What Al said. Everything Al said. Check your soil. Is it clay? Are you overwatering and suffocating the roots? Pick off all the fruit right away, the fruit should be ripe by now. If your soil isn't saturated, fertilize heavily and water in well. Fertilize every month through November to see if you can save your trees. Be sure as Al has mentioned to use a high quality fertilizer especially formulated for citrus that include micronutrients. Get to a good garden center for advice on fertilizers. I like Grow More Citrus & Avocado Food, but it may not be available in your specific area (not sure where you are in CA.) To post photos, upload to a photo sharing site like www.photobucket.com. Once uploaded, copy the HTML code (NOT the url of the photo) and paste that HTML code right into your message. When you click "Preview Message", your photos will then be embedded right into your message.

Patty S.

My tangerine is starting that. its an indoors tree lol

Any way.. I plan on giving it some lilly grow, which is high and I mean HIGH in iron, phosphates and other lovely things citrus and lillies just can't get anough of , plus its cheep lol

Crap tone of all kinds of Nitrogen, iron zince potatsuim, inc. Its amazing really how water lillies take all most the same as a citrus. Save its a lot safter, since its fishy safe, and if it kills a fish, your toxisity could make a human sick.

wolf, your mandarin really needs to be fertilized with a fertilizer formulated for citrus that also contains micronutrients. Dousing it with iron may not resolve the issue, as most likely, it's not iron deficiency you're dealing with. A very good product for indoor citrus is by DynaGro. It's called Foliage Pro. Its a water soluble fertilizer with an excellent NPK ratio for citrus, plus the full complement of micronutrients citrus need. The ideal NPK ratio for citrus is 5-1-3, so any permulation of that or close to that would be suitable for citrus. And, yellowing and leaf drop may also be an indication of a change in light levels. Citrus are really outdoor plants and need a lot of sunlight. So, be sure your tree is receiving adequate natural light, or a supplemented with full spectrum lighting. Lastly, be sure your tree is in well draining potting medium. You're probably better off posting over on the Citrus Forum, where there are quite a few container citrus experts there, if you need more help with your mandarin.

Patty S.

In some Calif. counties, the exotic Asian citrus Psyllid is found to be infecting citrus trees, my area is affected. It's moving into other counties. It's very damaging to citrus, but worse it hosts the terminal greening disease--the leaves and fruit look part green part yellow. I wasn't able to see your pictures.

On my navel tree, hundreds of mature dried leaves fall off, they're folded looking and have no signs of disease. It has the psyllid, but I'm trying to save it. I pull off all new tender growth that looks terrible. For yellowing problems, try using greensand for a natural magnesium supplement, it helped the yellow go away on mine completely, after a few months last year. Also I give it triple 15 fertilizer, or if you want organic, blood and bone meal with the greensand. Leaves are falling off dry and folded, but weren't yellow. It seemed to help the tree last year when I wet it down, then threw diatomaceous earth over the leaves and any young fruit, this is supposed to kill insects by a mechanical means, not chemical-the insects can't walk on it. It's due for another diatomaceous earth powdering, but I'll wait until no blossoms, so to not harm bees, and when no chance of rain to wash the earth off. I think the Greensand and the D. Earth both helped the psyllid problem. If greening disease is present, the tree is supposed to be cut down and disposed in doubled vinyl bags (like asbestos ceiling popcorn!)

I'll add a link about the Asian Citrus Psyllid damage and greening disease.
For yellowing issues use Greensand, natural magnsesium. Still, my oranges aren't ripening right, they stay part green and never get sweet. The leaves used to look like the ones shown in the link, but look better now.

My 30 y/o lemon tree was destroyed by the Asian Psyllid, I'm taking that tree down--never seen such bad damage to leaves in my life-unbelievable!! Will try to post a picture.
Good luck.

Here is a link that might be useful: CA Pest and Disease Prevention Program

oops, the original post is almost 3 years old!! I wonder how the tangerine trees fared?