My only thought is wondering if daily watering is causing the tree roots to grow closer to the soil surface. Why are you watering daily instead of once a week deep watering.

You have a very beautiful place. I suggest getting a certified arborist there ASAP.

Thanks Rosie,

We only water the lawn daily during the hottest summer months, out of necessity I guess. Common practice here in AZ. While I realize it is better to water less frequently and deeper, it is more difficult with our fast draining soil and very low humidity. We also have bare areas that we've re-seeded and are trying to get filled in. Also, just to clarify, some of the plants in jeopardy are not receiving daily watering. They are on a drip system that waters every 3-5 days. So, not sure it could be related to that.

As for the arborist, unfortunately we don't have any in the area that really know their stuff. I had one of them come by and diagnosed it as root nematodes... I thanked him and sent him on his way. I'm not in a panic yet because the worst tree is slated for removal anyway, due to limbs threatening our home. The rest of the trees/plants can be corrected, I'm sure.

Hope others will jump in here and offer help.

I know nothing about root nematodes, but wonder if you're investigating this. Perhaps you could talk to your county ag agent.

Another thought - seem full of them this a.m. - have you cross posted to the TREES forum?

Good idea to post to the trees forum.

I've seen root nematode damage before and in my opinion this doesn't fit, but if others out there disagree, I'm all ears. If that is the correct diagnosis, I have some property for sale :)

The need to water daily indicates there is not enough organic matter in the soil to hold sufficient water, which is not too surprising in Arizona.
What is the humus level of your soil?
Have you checked drainage?
What kind of life is in your soil?

Raising the level of organic matter in our soil is an ongoing process. In all the shrub/perennial beds we covered with a 4" layer of wood chips. We have great quantities of these available to us, so we refresh them on an annual basis to spruce things up. They are never incorporated into the soil.
In addition we leave all of the leaves that fall in place and mulch them into the lawn. By spring, it is hard to find a trace of them because the soil critters consume them so rapidly.
Our property has a large pond at the lowest point that collects runoff in large rain events. As regular maintenance I remove large quantities of elodia and cattails which I add to our compost pile. Other compost ingredients include weeds and poultry waste from our coop of about 25 birds. Most of this is used in the vegetable garden.
So I think we have a pretty healthy organic level in our soil that is improving over time. Drainage is definitely not an issue, except that it probably drains too fast.

The pale leaves with dark veins is typical of iron deficient plants. In AZ that is quite common.

You need a good soil test, because you might have plenty of iron and too high a pH, or you may have little iron and a lower pH.

Yes...soil test in progress. I'm betting on high pH, which my concern would be that with all we've been doing with mulching, the situation should be improving. Unless our water is high in alkalinity and then every time we water we're worsening the situation. I've heard some growers in our area have had to acidify the water prior to irrigating.

Looking forward to hearing soil test results. Impossible to acidify your water pre-irrigation, probably. You've presented a unique and intriguing problem.

The soil test might tell you something. But I bet it is not the cause of your problem. It sounds like you're doing some things to improve your soil. But in AZ I suspect watering daily is not beneficial to the trees or the soil, only the grass. Start with your tree. There is grass obviously up and around the base of the tree. This is not good for the tree. Get down there and remove the grass (vines?) growing around the tree by hand. Secondly, is the root flair for this tree above the ground? It should be. Exposing the root flair if it is buried will also help overall health and vigor. A buried root flair is prone to adventitious root girdling of the trunk of the tree. Finally, in my area, 25 years is starting to get old for a Cottonwood. Sure, sometimes they live longer in the wild, but in the wild cottonwood typically grows very close to water. Does the cottonwood have a steady water source other than your daily irrigation? They grow fast and die fast. The tree could be declining because of age. A good arborist should be able to identify the cause of the problem. Good luck.

That pear definitely looks like a problem with alkalinity. Those trees are sensitive to alkaline soil conditions and tend to yellow and burn at the edges just like you see there.

As far as the cottonwood, I'll just give dogwind a "ditto".

In regards to acidifying your water probably being impossible. Not quite impossible. It can be done and is done regularly in commercial growing situations but requires you to either use a sulfur burner or inject acid directly into the line, typically N-pHuric or sulfuric. It would require special equipment and expertise. This would likely be somewhat impractical for your situation (although I don't know how important your trees are to you, how much time and money you have to spend, or if your water is even alkaline or high in bicarbonates.)

Around here, a 25 years old cottonwood is a teenager. There are hundreds of them in the valley we live in that are 4 times as old as this...and the older ones that are declining seem to do so by losing out to gravity. They drop large branches over time until they've been reduced to a stump. Even then they still grow, and if it weren't for people removing the stumps they'd probably continue on for another fifty years looking like a bonsai gone wrong...so definitely not age related.
Please explain why grass growing at the base of a tree is a problem. I always try to plant some sort of ground cover around the base of trees. The benefits in my mind being that it shades the root zone and encourages beneficial soil life to colonize there. It is no different then having a thick layer of mulch. While grass is not my first choice I don't see a problem with it. There are healthy mature trees all over this country growing in lawns, and old growth forest trees with dense groundcover at their base, so I think it is fine for the tree.
The more I investigate this by looking closer at the different plants throughout our landscape, I am becoming increasingly aware that it is probably going to be an alkalinity problem with the water. Plants that are more tolerant of alkaline conditions are thriving while adjacent plants are turning chartreuse.
Gargwarb, I am a little familiar with acid injector systems, but what do you think the long term effects would be on the environment? Specifically the groundwater? The trees are very important to us, with exception of the cottonwood that is going to be removed this winter. I like to be practical, so the pear would probably be removed and replaced with a more alkaline tolerant tree.
Thank you everybody for the input so far!

Please explain why grass growing at the base of a tree is a problem.
Sure, there are a number of reasons. One problem is that the watering regime for grass is usually different from that of the tree. You'll often end up trying to meet the requirements of one to the detriment of the other. Also, people tend to adjust sprinkler heads to spray all of their turf...right up to the trunks. Spraying trunks directly can open them up to trunk and collar rot pathogens that require free water to enter the host. This can be exacerbated when something sits right up against the trunk, allowing the bark to remain wet for extended periods of time. This could be mulch or another plant.
Grass also competes with the trees for nutrients (and could potentially be a factor in the yellowing of the cottonwood).

It's not that growing grass under a tree is a death sentence, it just introduces a host of potential stress factors. It's a lot like eating cheeseburgers is for us. If you eat double western bacon cheeseburger regularly, are you guaranteed to have a heart attack? No, in fact lots and lots of people get away with it. But you increase the chances unnecessarily.

The acid injection won't get into the ground water. Sulfuric acid (either from straight injection or through the use of sulfur burners) will decrease the ph of the water by reacting with bicarbonate, thereby neutralizing both the bicarbonate and the acid. Typically your acid rate is calculated to neutralize a lot, but not all, of the bicarbonate (usually 10 ppm or lower is good). In other words, all of the acid has been neutralized by bicarbonate before it even reaches the spray nozzle. If acid is over applied, it will react quickly with organic matter and lime in the soil. In either case, the products of acid/base reactions are a salt and water. In alkaline soils that contain lime, and in high bicarbonate water, the primary salt created as sulfuric acid (H2SO4) reacts with lime (CaCO3) and bicarboate (HCO3) is calcium sulfate (CaSO4). Hey presto! You just made gypsum!

As far as the N-Phuric (CO(NH2)2 * H2SO4) goes, it acts a little differently. It reacts with bicarbonate (HCO3) and forms sulfate, carbon dioxide, water and urea. Since it's a synthesized form of urea, you wouldn't want to do this if you need to stay organic but it is a much safer and less complicated alternative to handling sulfuric acid and it provides nitrogen for plant nutrition.

I agree that picking something with more tolerance to alkalinity than the pear would be a good idea.

Oops, I meant 100 ppm bicarbonate or less.

On a side note, alkaline water could be a contributing factor to alkalinity in the soil but I would imagine that the bigger factors are likely to be the presence of lime and the effects of an arid climate and its relationship to the physical and chemical development of the soil over a long period of time.

I agree that spraying the trunk directly with water is a death sentence...which I avoid doing. Remember we are dealing with a cottonwood that naturally grows in riparian areas and is accustomed to having roots and trunk base flooded on a regular basis. One huge old tree at the lower end of our valley grows in a meadow that is standing in water 9 months of the year and it seems to be doing very well.

As for the alkalinity of the soil and it's development over time in an arid environment, why would the tree grow fine for 20 years of it's life before showing signs?

And.... This is the first year I've had this problem showing up in annuals. Interestingly, every plant showing this problem is within the probable root reach of the cottonwood. You mentioned grass depriving the tree of nutrients, but isn't it possible the tree is depriving the entire area of nutrients? I've always thought that is why it is hard to grow even shade loving plants under mature trees.

I was talking about trees in general. I am aware the cottonwoods riparian. You asked and I answered your questions? You can take the information or leave it.

As far as the cottonwood and alkalinity, I don't,t think that's likely to be an issue. Cottonwoods are relatively tolerant of alkaline conditions and your cottonwood pictures don't look like alkalinity induced chlorosis. I was referring to the pear and other plants that are more sensitive to alkaline soil conditions.

Could the trees be competing with everything for nutriens? Sure. Why would suff do well for a long time and start showing problems now? I don,t know. There are so many factors that could be involved that I wound need to be there to give you a good answer (That,s why I only talked about a couple of specific factors rather than saying, "I have the answer to all of your multiple issues")

I thought I'd post a couple of pictures of cottonwoods in the neighborhood exhibiting some of the same signs as mine. Neither of these have turf grass around their base and neither are watered by any type of irrigation system. They are both presumably tapped into permanent underground water. By presumably I mean the water table is about 18' down here, and they would not survive here without irrigation otherwise.

The distant shot is of a very large cottonwood growing along the wash, where the water table is very shallow. But dry on the surface unless we are currently having a precipitation event. The light discoloration is how ours looked a few years back, and my guess is that these trees will meet the same fate. Time will tell.

I've also included some photos of other plants that show symptoms. The sempervivum does not receive any irrigation water, and in other areas of our yard it is doing very well. Potentilla, Euonymous, and Barberry are all affected plants that in my mind should be alkaline tolerant. Not sure about the poppy, can't remember the species, but it receives no irrigation either. All of these are located near the troubled cottonwood, and for the most part grow elsewhere in our yard with no problems...yet!

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Gargwarb,

I hope I don't seem argumentative, not my intent at all. I very much appreciate you taking time to respond. Just trying to take what you're suggesting and see if it fits. If not, I just want to consider other options. You say, "multiple issues" but I am thinking that they are all related to the same issue. Maybe not, I dunno.

The biggest changes for your established trees are the new lawn and irrigation system. Construction, trenching, compaction, sod, and then the insult of the tiny, daily sprinkling.

Speaking of grass, little is said about this but some turf species exhibit allelopathic properties against some plants, including trees. EEK.

Well... I was hoping the pictures of the other trees in the neighborhood without lawns beneath them exhibiting the same symptoms would dismiss the lawn as the cause. While I agree with all that is being said about grass around the base of trees, the spraying of the trunks, and the daily watering not being ideal, I think cottonwoods are more tolerant of this. Not to mention the fact that out of the 10 trees in our lawn, this is the only one showing trouble.

Well... I was hoping the pictures of the other trees in the neighborhood without lawns beneath them exhibiting the same symptoms would dismiss the lawn as the cause.

Here's the thing. Trees aren't like people. When something is wrong, they can't get the sniffles, they don't get a rash, that can't tell you that they have a soar throat or a headache.
They can turn yellow, they can turn brown and they can die. Of course, I'm over-simplifying but not by too much. The fact is, plants have a relatively limited set of symptoms for a vast array of problems. There are many things that can cause trees to yellow. There are many things that can cause the other trees in other pictures to yellow and they are not necessarily the same things. You're problem may or may not be the grass. The problems with the other tree are...who knows what.
I don't think anyone here has said with certainty that the lawn is causing the problem. We're giving general information based on a description and a couple of pictures. None of us has been there to look at the whole situation.
Knowledgeable people are throwing out strong possibilities for you to consider and investigate further. If you choose to disregard the information out of hand because you see other yellow trees in the area, rather than giving our information serious consideration, that's cool. At this point, you probably need to pony up the dough and get an arborist or other professional horticulturalist out there to look at the situation first hand.

Gargwarb,

All the strong possibilities are being received and considered, trust me. For that I am thankful.

As for ponying up the dough for an arborist or professional horticulturist, that is advice that can be given to every poster on this forum. It is totally dependent on others contributing whatever knowledge or experience they are willing to. If you feel you've contributed everything you're willing then that's your right, and thanks for that. Others are willing to offer advice and then consider other options based on continued feedback from the original poster.

I will post soil test results as soon as they are available.

Well here it is...

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You can purchase pelletized sulfur, which is the only way I'd consider putting it down. You can apply the pellets with a spreader, irrigating it in afterwards. You may want to consider running the cycles long enough to disperse the pellets and carry the sulfur into the soil system.

Rhizo, do you agree with the application rate? Based on another thread I read, this may not be enough.

Quoted from the other thread:

"The rate of sulfur given by the lab is very conservative. It translates to about 2 lbs. of soil sulfur per 1000 sq. ft. With a pH of 7.7 and CEC of 20 I would bump that up to about 10 lbs. per 1000 sq. ft. incorporated to a 6 to 8 inch depth before your next croping cycle. The test does not mention lime content. Lime can increase the soil's ability to buffer against downward pH adjustments and an increase in lime means a higher rate of sulfur required."

Here is a link that might be useful: First soil test some help

Dittos on the high pH, 8.0. Caution on trying to apply too much sulfur in one app! Incorporated, higher volume, surface applied (as in conjunction with core aeration) much, much lower volume or things fry from too much shallow acidity.
But my comment goes back to the second picture in the OP. Bleeding from the wound(s) from branch removal(s) indicates wetwood disease, common to cottonwood. That may be an additional problem affecting the tree.
hortster

it is interesting to see that your sulfur level is very high, yet they recommend adding more sulfur. This is an organic gardening forum. A high quality compost, broadcast over the property, will do more to improve your soil than sulfur by itself will, by lowering the ph, improving the carbon level, and making trace elements available on an as needed basis. Your lab does not recognize carbon or organic matter, which is a big problem because it is essential to healthy soil.

Here is a link that might be useful: Texas Plant and Soil Lab

I questioned the addition of more sulfur as well. It was explained to me that there's a difference between sulfate and sulfur. Maybe somebody can explain that better than me.

First, there is nothing "non-organic" about adding sulfur to the soil. Second, a half-inch of compost under the tree isn't going to lower the pH as 'quickly' as sulfur; the tree is not happy and you want to lower its stress as quickly as possible. Third, maybe Garg has an elevator phrase for this, but elemental sulfur is more readily used by soil bacteria to convert to sulfuric acid, which lowers pH; the sulfate ion may bind with something else & not do the job, or buffer the S reaction. Hard to say. This is not to say OM application is a waste of time - this is to say time shouldn't be wasted. Lastly, one hopes the lessons here about the basics of soil can be applied to the business in the future - those PedOCaL soils in that place have high salts and pH for a reason. Plenty of plants don't care for it.

Dan

How was the soil sample taken? It seems like everything is "Very High" almost as if chemical fertilizers were used.

Nope, no chemical fertilizers have been used on this property in the 7 years we have lived on this property.

The samples were taken by removing the first couple of inches soil and then digging approximately 12 " of soil. Several samples were taken from different areas, and all was mixed together before scooping enough to send to the lab.