I see your posting was made on Nov. 6 having no reply. So
I'll have a go at this one.
Die back can be from under or over watering the citrus. although I updated to Win 7 on a Sony. The photo you posted is not viewable.
I do suggest you remove any dead or living matter such as dead leaves and grass from the top soil for this will contain moisture and pervert aeration to the root system.
Most of all citrus failures are do to the lack of aeration to the root systems. being soil drainage and either over or under water. A good soil mix is one that offers good drainage and aeration to the root system.
Perhaps the problem maybe somewhat more . I strongly suggest the findings from others. Regards. plant54

I am NO expert and do not grow citrus inground. Too cold here. But I will make an attempt to help.

How long have you had your orchard? And how familiar are you with growing citrus?

Do you live in an area where canker or greening disease is present?

Yellowing between veins is usually a sign of deficeincy. What is the pH of the soil?

Black sooty mold is usually a sign of scale. Ideally this should be washed off because it is blocking sunlight from reaching the leaf surface and also not allowing oxygen to enter the leaf.

White fuzzy substance could be mealy bugs or a fuzzy scale called cushion(?) scale.

At this point stop all the spraying. The leaf pores may be getting clogged and not allowing transpiration to occur.

Cornmeal. This is something that I once read about and now use. Although its success will depend on what the real problem is, but it will not hurt anything and may help. Get a few kilos of cornmeal (ground corn), sprinkle very liberally around the tree, rake it in and water. In 3 to 4 weeks you may see healthier tree.

If you have questions about anything I've written, please feel free to ask.

What is the cornmeal supposed to do? I have never heard of using it as a supplement. I have had good luck in the past using grits to get rid of fire ants in the yard.

Lisa

Basically, the cornmeal encourages the rapid growth of friendly fungus (and other beneficial microorganisms). This friendly fungus then kills off pathogenic fungus.

This worked for me with my Key lime, which started to decline. Just repotting it did not stop the decline, but it turned around after the cornmeal was applied.

citrusnut, where do you get the cornmeal from? TIA.

I got Quaker yellow cornmeal at my local supermarket. It was in the baking section near the flour. You will find yellow and white cornmeal there. I was told to get the yellow, so I did, but don't know why yellow is better.

People say that there are other places to buy it like feed stores, but the only place that I found it was the grocery store.

Yoggity,
About watering your trees, is the ground beneath your trees lower than the surrounding area of any of those trees that are suffering from twig dieback? If so, and if those trees have the yellow leaves or leaves that have green veins but yellow areas outside the veins and the yellow areas ever increasing so that an entire leaf may become yellow? If so, I would wonder that the trees may not have sufficient drainage. This could cause an Iron deficiency and cause other problems as well -- like the declining of a tree ... including twig dieback and leaf drop.

Those green leaves that have brown spots that are surrounded by a yellow coloring around them reminds me of Alternaria.

I would like to write more, and will wait for you to reply--maybe not till this evening.

Hi All, many thanks for the replies. I just got back from a trip so am just getting to these.

plant54 this is a link to an album with the photos in case you still cannot see them http://s22.photobucket.com/albums/b336/yoggity/Trees/?albumview=grid

To start off, I would agree with everyone that the general problem is poor drainage. This is former lakebed and very dense sticky clay (I have broken trowels right off the handle in the stuff). Recently I dug a hole for a new tree and filled it with water to see how it drained and it took almost 48 hours for it to drain.

This said, I have some questions about making the best of the situation:

Watering:
1) We are cutting back watering to every 14 days and generally just giving a pretty good soaking. Should we be more measured in the actual amounts of water?
2) Being a tropical climate with heavy sun, even though 6" below the surface it is still moist or even pure water, the top bakes and cracks within a day or 2 after watering. Would plastic or mulch covering around the tree help
3) Is it advisable to not water for an extended period of time (say 3-4 weeks) to make sure the soil really dries out once and for all, then aerating and going back on the appropriate regimen? Would this help? Would it hurt?

Aerating:
1) What is the best method to aerate the soil? Can it be done with the special aerating drill bits I have seen?
2) Once aerates, should we mix in some organic mulch, liquid humus, or something?
3) Is this best done during certain time of year? We are entering a brief spell of cold (never freezing) and then a long, super sunny dry season until July.

As for you other questions regarding soil pH and the pests, let me get outside and do some legwork and get back to you with more details. This is a home orchard, we are not professionals, do not sell but rather give away the fruit to neighbors, and consume much of it. Again, I appreciate the responses and hope to continue hearing from you.

Thanks,
JNR

Okay, here is a summary of pest/disease possibilities:

No sign of spider mites or scale.

Wooly Whitefly:
I believe this is the main culprit. Explains sooty mold, shrivelled leaves, dieback, fuzz under leaves.

Citrus leaf-miner:
I believe this is at work on some trees, although I have yet to find a live bug. I did find a folded over edge with a cocoon in it. As I understand that this pest isn't totally devastating.

Greening Disease:
This was very disturbing as I read it because so many of the symptoms coincide with my situation. However, upon a more detailed reading, I do not think it is at work because the yellowing does not (yet) affect whole sections of the tree and is symmetrical across the vein. Also, I still have exceptional fruit quality.

Canker:
Fruit are good, even on sick trees. Leaf-miner mottled leaves do not have canker. I recall last year finding a cankerlike fruit, but it is very rare. Definitely no infestation.

Here is what I am doing:
1) Ant control... not sure exactly what I will do yet (I heard cornmeal works here too), tanglefoot is not available in Mexico that I know of, so probably baits
2) Powerwash leaves, if I can find a powerwasher
3) Insectidal soap with horticultural oil spray
4) Look for natural predators to control biologically, again not sure if available down here
5) Rethink chemical fumigation so as not to kill natural predators

I would appreciate any commentary and especially opinions/tips on my control strategy as far as what works, how often, etc.

Thanks,
JNR

Oh also, does not seem to be Alternaria. I have seen navel end rot on a few of the limettas and seedless limes I have, but usually this is long after they have been picked or left on the tree for way too long. Seems more like natural rotting to me.

However there is an occasional small blob of gummosis resin, usually on branches and upper trunk, never at graft or lower trunk. This would support the lack of drainage and excess soil humidity right?

I see no signs of fungal or bacterial diseases in the photos. Your speckled limetta is interesting -- I'm wondering if there's a bit of molybdenum deficiency there. Do any of your fertilizer materials contain any Mo? It doesn't take much. I don't know of anything else that makes yellow spots like that, since you say there are no insects involved (scale feeding on the undersides could mimic that symptom).

As for your tangerines -- water damage to the roots would produce symptoms like that. You don't want to let the trees dry to the point of severe wilting, but it's probably good that you're watering only every 2 weeks. Do you know the soil pH? It may be high. If you can test it, try to get the pH below 7, and preferably below 6.5 with sulfur or iron sulfate. But I would not just throw some of those materials on, unless/until I'd done an actual test of the pH.

Malcolm M. Manners
John and Ruth Tyndall Professor of Citrus Science
Florida Southern College
Lakeland, FL