A friend of mine lives in suburbs of Phoenix, AZ, and needs advice about a lemon tree that shows signs of disease/stress. Details about the tree: it’s a mature tree, about 12 ft high, last year it had a bumper crop, but has been showing signs of stress for a few months. Specifically, leaves become yellow and drop (please see the photos below). There are no obvious signs of any insect/pest activity on the tree. It is regularly irrigated (once every 3 days) and occasionally fertilized by magnesium and a “Citrus food”. Another lemon tree nearby and under the same care and conditions is doing just fine and has healthy dark green leaves. Other trees and bushes on the property (not citrus) also seem to be ok. Please help diagnose the problem!
What is the drainage like?
Drainage is fine. As you can see from the last photo, the tree is on a bit of a slope, so there is never standing water near the tree.
Is the soil clay?
I’d say it’s too dry or there is a root issue. How much is it being watered?
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The soil type is Eba-Pinaleno complex, 3 to 20 percent slopes
https://soilseries.sc.egov.usda.gov/OSD_Docs/E/EBA.html
https://soilseries.sc.egov.usda.gov/OSD_Docs/P/Pinaleno.html
This is very gravelly clay loam/very gravelly loam, very deep, well drained soil.
It gets deep watering once every 3 days, in morning.
With that soil it’s certainly not poor drainage. I still think it could be too dry. Is it drip irrigation? That’s not always that reliable.
How do surrounding trees look and are they being watered the same?
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For each watering, they fill up the basin around the tree (the basin can be seen on the last photo). The same for the rest of the plants (another lemon tree, a peach, an olive, and some bushes). All the trees look fine except for this lemon tree. Of the two lemon trees the larger one is stressed.
I agree with @fruitnut that it could possibly be a watering issue, but you also said he only occassionally fertilizes…some lemons are greedy feeders and require monthly fertilization (at least down here) during the growing season. Chances are it’s not getting enough to eat…maybe a good dose of fish emulsion would help it perk up, then keep up with the feedings every month.
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