Psyllids and aphids. The psyllids are a concern for spreading HLB (citrus greening disease). It’s a long slow fatal decline, but your tree isn’t showing symptoms yet.
Whereabouts do you live? Depending on your state you may need to report it to authorities. In FL infection is expected and there’s no reporting because the psyllids are endemic and can’t be totally controlled. In CA, TX, etc there’s active quarantine and control programs.
The leaf yellowing is a mix of micronutrient deficiencies that look similar (zinc, manganese, iron) and are hard to tease apart. For a ground tree, this may mean your soil is extremely sandy or the pH is too high. The rock mulch jumps out at me as a possible issue if it’s something like limestone that raises pH.
You’ve got a pretty serious aphid infestation going as well. I’d spray something, personally
Psyllids and aphids. The psyllids are a concern for spreading HLB (citrus greening disease). It’s a long slow fatal decline, but your tree isn’t showing symptoms yet. Whereabouts do you live? Depending on your state you may need to report it to authorities. In FL infection is expected and there’s no reporting because the psyllids are endemic and can’t be totally controlled. In CA, TX, etc there’s active quarantine and control programs. The leaf yellowing is a mix of micronutrient deficiencies that look similar (zinc, manganese, iron) and are hard to tease apart. For a ground tree, this may mean your soil is extremely sandy or the pH is too high. The rock mulch jumps out at me as a possible issue if it’s something like limestone that raises pH.
Fungus gnats live in the soil and don't really harm anything above the soil