What caused a healthy citrus tree to experience a sudden die-off?

One of the most common causes of sudden death in trees is root rot usually caused by poor drainage.

Q. I’ve read your articles for many years and have gained much knowledge. My wife and I own an acre of land in the outskirts of Moreno Valley, with approximately 70 assorted citrus trees. We have a dirt street with a cul-de-sac that leads to our house, where we planted two Cara Cara orange trees approximately 17 years ago. They are a foot and a half above the native soil. These trees have done phenomenally. In May 2023, I noticed one tree turning a slight yellow, and by the end of August it had lost 99% of its foliage. I have since taken out the tree. The other tree is still doing very well and its fruit are large and sweet. If you have any ideas of what may have caused this sudden die-off, please help me so that I may try to prevent it from happening again.

One of the most common causes of sudden death in trees is root rot usually caused by poor drainage. This doesn’t seem to be the cause in this case since your trees are planted on a berm (a very effective way to deal with soil that doesn’t drain well). Citrus trees have a relatively shallow, but dense, root system. This can make them sensitive to irregular watering. If they are on drip irrigation, it’s possible that there was a drip failure for just the one tree. 

Citrus trees don’t do very well when planted in a lawn, since grass roots will out-compete tree roots for water and nutrients. As if that wasn’t enough, I’ve seen cases where a tree has been girdled by repeated strikes from weed trimmers. This is not likely in your case, but worth mentioning since it happens to many homeowners.

Yellowing and leaf drop is common in citrus trees that are deficient in nitrogen and/or iron. Our native alkaline soil tends to bind iron, making it unavailable for tree roots. If you see leaf yellowing (chlorosis), apply nitrogen (all-purpose or citrus) fertilizer and iron. In your case, only one tree exhibited chlorosis before leaf drop, but there may have been a localized nutrient deficiency in your soil.

All commercially available citrus trees are grafted onto a hardy rootstock, either sour orange or flying dragon. Sometimes the graft will fail, and the top half of the tree will die but the rootstock will survive. If there’s growth below the graft, this is probably what happened. If the rootstock is allowed to sucker and grow, it will produce incredibly bad-tasting fruit. Graft failure is usually a random occurrence, especially in commercially produced trees. Since one tree remained healthy while the other perished, this would be my best guess as to what happened.

If you wish to replace the lost tree, I advise not planting it in the exact spot that the dearly departed tree occupied, but it should be okay in the same general area.

Los Angeles County

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San Bernardino County

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