I believe it is just old and has lived as long as it could. Do you know it's age? My place has been here since 72 and my grapefruit tree died at about the age of 30 yrs.
and then the hurricane really did it in.

Citrus Greening Disease. :(
See link below.

Carol in Jacksonville

Here is a link that might be useful: Citrus Greening Disease

Get a bottle of turfpro with Iron and follow directions for foliar feeding making sure alot runs off into the ground. You may want to wait till the last chance of frost passes as it will encourage a leaf flush. It is a Treatment of last resort for me.

I tried to upload a recent photo but was unsuccessful. Tree was a sad sight with only about 10 % of it's normal foliage. Appreciate the feedback tho, - gots ta look at the glass as half full. At least I got the 3 great harvests out of this wonderful producer. A new appreciation for Ruby Reds. Thanks all.

You said "killing all grass underneath"......how did you go about doing that, manually or chemically?
I have a Ruby Red for probably at least 15+ years, love it. Once it got started, only had about 2 off years when it had minimal production. The girlfriend would probably dump me if I lost it and didn't replace it with the same.

Hope it come back for you.

DM

Hi DM. I just sprayed the ground around the tree with a common grass & weed killer, then put down some pine bark mulch. Not sure how all important doing that was, as the tree obviously thrived for many, many years with grass growing under it. Just following the advice gleamed from a couple of online sites.
Am tempted to get two tree guys in to cut the old tree down, but will wait awhile. May plant a young 5 - 6 ft tree nearby just in case it is dying, - have come to love those fruits as you guys do.

Hi
All my citrus trees were removed by the state about 3/4 years ago two of my neighbors and i replaced two years ago Every one of the new plants looks terrible and several have died. Don't know what the problem is but never had a problem with the originals. have only a mandarin left and though it grows and flowers the fruit is terrible. Hope you have better luck with replacements giving the mandarin one more year good luck gary

Sadly, the problem with all of these citrus trees is almost certainly Citrus Greening Disease. (See my prior post, third from the top, above.) Coincidentally, Tom's Digs of the Orlando Sentinel posted an update on the disease today. See link below.

Carol in Jacksonville

Here is a link that might be useful: Despicable Disease Claiming Dooryard Citrus

If the common grass and weed killer that you sprayed was Roundup, that is what killed your tree and there is nothing you can do to reverse the problem. I had this unfortunate experience with a healthy grape fruit tree and a healthy, very large and productive orange tree. Killed them both before I realized what was the culprit. Citrus tree roots are very shallow and Roundup will kill the tree.

What kind of weed / grass killer did you use? The grass was probably the best kind of cover for the tree..

The spray I used was not Roundup. But my spraying had nothing to do with my huge Ruby Red tree to decline, as the spraying was done long after the tree was obviously in trouble.
After chatting with my neighbor this morning, who also has a 20 + yr old grapefruit tree,( not a Ruby Red ), that has just gone into decline this year, a full year after mine, ( she never sprayed anything underneath ), I went out and bought a new Ruby Red at the Home Depot in North Port. A 15 gal pot, cost $60,..will plant in within the next week. My last attempt to keep a steady supply going. The jury is still out on the big 18 - 20 footer. Will give it another year of TLC.
Thanks for the comments just the same.

I retrospect, with the news this morning of my neighbors big grapefruit tree also now in the same condition mine is, I am afraid that Carol in Jacksonville's comments above may have hit the nail on the head. If, upon further scrutiny, this appears so, I will immediately have my big tree cut down and the wood carted off to the dump. Hope this is not whats happening but will keep my ear to the ground. Seems too convenient having two big, healthy citrus trees on adjacent lots suddenly die within a year of each other. Hopefully there's another, easier to deal with, reason.

Well, after carefully mulling my situation over, I am convinced that the two year steady decline of my large tree is caused by either it's age, ( max life span averages 33 - 35 yrs for these trees, mine is about 30 y.o. ), or it has citrus greening.
In either case the tree is most likely a goner, so yesterday I had over my two guys to cut it down and plant the new Ruby Red I bought 4 days ago at Home Depot.
The following is the pictorial sequence of a sad demise and an optimistic beginning. Am hoping its just an old tree as Wanda said, and the more I think of it ( a dangerous thing for me ), the more I feel she is right. Felt I had to do something, instead of just wasting another year looking at a slowly dying tree. Want to get some Ruby Reds back in production asap.
Now hoping I can download the pics. The old tree that was just cut down was growing right behind the pic of the new 4 ' tree.lol

This post was edited by jofus on Tue, Jan 8, 13 at 10:04

Slowly dying Ruby Red.

..gone ! This is the new 4 ft tree,..hey, can see some tiny fruits already !!!! ( smile )

That tree didn't look so bad, to me. Supposedly, people are having some success with intensive nutritional sprays. Might be too costly/too much work for most dooryard citrus growers, though.

Here is a link that might be useful: Citrus Greening Management