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I recently bought a house in Arizona with two very tall trees in the front. The lawn itself is normally flooded once a month by the irrigation system to give water to the plants, but during the purchasing process the seller skipped a month. During this time there was a record drought, and once I moved in I noticed that one tree looked pretty sickly.

The "leaves" on this tree are pale and sparse compared to the healthier one, and there are slight vertical cracks on the trunk. My question is if this tree is dead, dying and in need of treatment, or just dormant and will recover on its own.

We got rain and irrigation just a week ago, so the soil is wet, but since the tree doesn't look any better I thought I should ask. The tree in question is on the right of this photo.

Tree in question is on the right

Update: Called an Arborist and this tree is dead. He cut off a few branches and found 99% of the leaves were dried out. If anyone is wondering, this tree is about 4-5 stories tall, needs to be taken down with a crane, and will cost 1.5k - 2k to cut down :(

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Those trees are probably Thuja plicata, also known as Western Red Cedar or Arbor Vitae, but could also be junipers of some kind or a Western US species that I'm not familiar with. In any case, two trees of the same species planted that close together should be equally affected by watering issues, because their roots are definitely overlapping each other in the soil, and by many other issues because of their proximity. Additionally, a recent drought would not show damage this quickly, as it can take weeks to months for an evergreen to show foliar issues. I would rule out watering then and look for other causes.

I think you could look at (in order of likelihood):

  • Wounds to the roots or trunk
  • Chemical damage
  • Nitrogen deficiency
  • Insect or disease

Wounds

Has there been any trenching or other construction near the tree? Of so, this could be the cause of the yellowing, although I'd expect the damage to be a bit more localized. If not, then you can rule this out.

Chemical Damage

This could be drift from an application of something like RoundUp to an area to the right of the photo, but then I'd expect the damage to be only to that side of the tree and also perhaps affect the same side of the other tree. Alternatively then, a chemical could have been deposited on the lawn on that side of the property and taken up into the tree via the roots. Perhaps a spill of some kind? Perhaps someone dropped way too much fertilizer on the right side of the lawn? This may have occurred many feet from the trunk of the tree (if arbs, then the tree roots spread out quite a ways from the tree).

Nitrogen Deficiency

I think that this is unlikely, as it would most likely affect both of the trees. Its symptoms are a yellowing of leaves through the tree, which does match what you're seeing, however, so it may be worth trying a soil test in the root zone of the affected tree (say, within 10-15 feet of the trunk). Do NOT treat for this without a soil test confirming low nitrogen, though!

Insect or Disease The best person to identify whether your trees are infested with anything is a certified arborist, but the fact that one tree is perfectly healthy and the other is in trouble kind of suggests that these are not a factor in the problem (both trees should be equally affected).

Ideas for these solutions come from the Ortho Problem Solver reference book.

One reference for you could be your state's Extension service. Most states' Extensions have websites (usually available from the state university with the best horticulture program). These have information that discuss local problems with trees, shrubs, and other plants and could perhaps point you in other, more localized, directions.

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  • Thank you for the detailed response! Given the proposed potential problems, it is weird that these two trees are faring so differently from one another. There is no real difference between the trees location, or anything harmful on either side. My thought is that if it's not a water issue, it might be a nitrogen deficiency. I might test for soil then. Do you think there's any chance that the tree might recover from whatever's wrong with it on it's own? Dec 20 '20 at 17:55
  • If it's a nitrogen deficiency then the tree should recover with treatment; otherwise, maybe not (depends on what's causing the yellowing). There's the possibility that the tree has actually reached the end of its life and is actually dying of old age. I recommend that you contact an arborist (NOT a tree-cutter) if the soil test is doesn't show a deficiency.
    – Jurp
    Dec 20 '20 at 21:07
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I wonder if it's possible your tree was effected with japanese bark beatle. I grew up in southern California and it was running rampant down there. That would explain the big defirence between the two trees. Have an arborist look at it. If it is infected then it will have to be cut down.

Nitrogen doesn't seem likely. Odds of it only effect one tree with both so close might be pretty hard.

Wounded might still be an option. Old owners could have trenched new sprinklers or dug up sewer or water line to the house for repair.

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