[HELP] My tangerine tree is dying?

Question

My father purchased a dancy semi-dwarf tangerine tree from Lowes about two months ago. It had leaves in all of its branches, all of the branches resembled a green-like color and it was growing a tangerine on it (the first photo shows an example of this). We decided to transfer it from the store-bought pot to the pot that it is in now, so it has more space to grow. There were also a frequent amount of caterpillars and eggs found on the leaves, so we decided to spray the tree occasionally with soapy water.
Everything seemed fine until two weeks ago, I noticed that leaves had started falling from the tree at a rapid rate. Until a week ago, I also had noticed that the branches were turning brown and eventually to a darker color than brown. I’ve done a bit of research and decided to move the tree to a location where it captured about 60-75% sun (previously it was catching about 50% of the sun during the day). I also have started only watering the plant in the mornings and only when the soil lacked moisture.
This tree means a lot to me as it was the last thing my dad bought before he passed, so any help would be amazing!

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Answer 1

Citrus can be quite finicky in container, so I understand your frustration. I'll help you to learn a few shortcuts really fast, though.

The first thing that we need to look at is container size. You will have to size them up slowly, starting with a container that is only 1 or 2 inches larger on all sides. Going up to too large of a container too fast will cause symptoms of overwatering and infection, as you see before you.

Treatment of the issue will be quite simple with the proper tools. A good fungicide is in order for the top of the tree, above ground. This article will help with fungicide use: https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm

Next, you will need to use a Citrus fertilizer. A good granular should be used 1 or 2 times per year, up to 4 if it needs. Using a Citrus fertilizer will be the best shortcut, since it is already pH balanced properly.

DOLOMITIC LIME (1/4 cup) and iron sulfate (about 1/4 cup) will be your best friends. The lime helps to stabilize the pH, while giving the tree much needed calcium and magnesium. Iron sulfate will provide the acidic touch to the soil while curing infections and providing Iron, which is a common deficiency.

Make sure to let this tree dry out down to 3 or 4 inches, thoroughly, between waterings. This will keep infections to a minimum. When you start to see roots on top of the soil, wait a year and transplant then.

Here is an article that will help you to grow these trees: https://www.gardeningknowhow.com/edible/fruits/tangerine/tangerine-tree-care.htm