TheGardenLady received this question from Tricia.
About a month ago I transplanted 2 young avocado trees (bought at the local nursery) into large containers (their spots in the orchard aren’t ready yet). I had watered them 2x/wk week in the beginning and then 1x the following week because the soil was staying wet and I was afraid there wasn’t enough drainage. One of the trees’ leaves started yellowing, even though it gave me flower buds already. So I stopped watering it, afraid that’s why it was yellowing (the other one is fine). It now has all the upper leaves completely yellow and some turning brown and curling. The lowest ones are still green. I’m not sure what to do? Water it or not? The soil still appears moist.
Fungus is the most serious disease of avocado trees, which may be the problem of your avocado tree. As you wrote, you over-watered the plant and also the plant might have had poor drainage in the pot you put it in. You should take your plant to your nearest Agriculture Extension
office for an accurate diagnosis. They can offer you, for a fee, lab tests and soil tests to see if your tree has a fungus. (see here)
It is difficult to diagnose the problem from just a brief paragraph. Here is what UCDavis has to say about avocado diseases.