Meyer Lemon Tree with Wilted Leaves and White Cake Under Leaves
It seems like I have been having trouble with my meyer lemon tree since I purchased it about 2 years ago. Initially the tree looked healthy and seemed okay. After bringing it home, I repotted it into a large clay pot, keeping the original soil in place, and putting general top soil around it with river rock on the top. The leaves then seemed to yellow and I thought that the problem may be 'wet feet'. So, at the beginning of this year, I carefully removed all the soil from the root ball and mixed down the potting soil mixture with 50% peat moss, a little bit of sand from the ground and Vigoro citrus and avocado plant food (12-5-8) all throughout. There has been no significant change with this new mixture. The tree flowered early in the year, but hasn't began displaying any fruit since. About 1-2 months ago, there was a rush of new branches and fresh green leaves. However, the older leaves are still yellowing as depicted in the photos. Today, I also noticed the 'white cake' on the underside of a couple of leaves which is causing me more alarm!
I don't have a way to measure the soil's moisture or pH. However, I think the soil is now properly draining with this new mixture in place. I have the pot positioned so that it gets watered from the sprinklers outside 5 days/week for about 15 minutes each time in the middle of the night. The tree is fully exposed in the sun all day long in Burbank CA. I do not treat the tree with any pesticides as I would prefer to avoid this if possible. I have noticed flys just hanging out on the leaves and seemingly not too concerned with me when I get close to them.
Can anyone please help me identify any potential issues you can see? Any information is greatly appreciated :)
Link to the album: