Kumquat is a citrus, this is a loquat. One that it is hard to believe is only a few weeks old. Anyway try searching "loquat leaf spot" and seeing if anything relevant comes up.

Embothrium - I received it at a few weeks old. I had it growing all summer to this size.

you may never get fruit and they bloom here (east central alabama, zone 7-8) in fall, normally peaking around thanksgiving. after that, our late cold blasts in february kill most potential fruit. i harvested a dozen or more loquats this past spring for perhaps the third time in 25 years. it is a nice evergreen here and grows tall if left to its own patterns. the sapsuckers love to damage the trunk. reminiscent of a magnolia after seasonal leaf drop in that the leaves are leathery and persist on the ground unless raked. the flower clusters have a nice floral scent, not as potent as true citrus, and it is good forage for bees in cool weather. easy to grow from seed if you ever get to harvest any.

I have several loquats in my yard and it's one of my favorite trees. Jeff is right about the sapsuckers (type of woodpecker) loving them. I wrapped chicken wire around my tree's trunk and round limbs with a diameter about broom handle size. They don't bother smaller limbs. I'm in zone 9a and my in-ground tree fruits prolifically. I have seen trees north of me that do loose their fruit in response to colder weather. Ballpark guess but I think you will get fruit if you don't go below 27F or so. It does bloom in winter, in fact it has begun to bloom now and will set fruit during winter and will be ripe in early spring....perfect timing for fruit-hungry folks after the winter! I would suggest making a nice big hole...much bigger than your pot...and adding lots of loamy material to loosen up your native soil if you have hard/compact soil. Loquats seem to just stay the same size if they don't like the soil they are in. I doubt you will be able to get your tree big enough to fruit in a pot but I could be wrong. They grow fast in the right soil and should fruit in just a few years but will probably be eight feet tall by then. It has a small root zone when the tree is little and is very susceptible to being blown over in windy and wet conditions. Hurricane Laura and Hurricane Delta recently blew my 6-foot tall tree over. I propped it back up and it looks as healthy as always. I wouldn't worry much about the spots and leaf loss. Guessing it's in response to the extreme wet/dry soil conditions a potted plant endures. They like a mesic soil conditions (not in standing water except for the shortest periods) Best!

Oh Ariel, I see you are in zone 7b. Yes, that's several hundred miles north of my zone and you are probably too cold to plant in-ground. Try a big 5-gallon or more pot. I think it would be a gorgeous indoor plant if it doesn't get too big.

adding lots of loamy material to loosen up your native soil if you have hard/compact soil

Never do this with planting holes for woody plants, because small areas of amended soil surrounded by unmodified soil of a close texture can either become collection points for water during wet conditions or prone to having water attracted away from them during dry ones.

Loquats in my part of USDA 8 collapse as though gone over by a torch during our sharpest winters, take years to recover afterward. So USDA 7 does seem like it would be problematic for them. And also consistent with above remarks fruiting of any consequence here is occasional at best, due no doubt to the winter flowering time.

Embothrium, I think you have to change your native soil it it won't support certain plants you wish to grow. I agree that people often do this the wrong way...make the hole too small and without irregular sides...and in effect create a pot in the ground where the roots circle and don't grow into the native soil. Another way to go is to build a raised bed and that works great in my area but it has to be pretty big if you plan to grow larger trees. I think you can create a healthy environment in poor or hard-packed soil, you just have to make the hole quite large, irregular, and by mixing the new amendments into the native soil rather than throwing out the original material. I like to extend the effective size of my irregular hole by working a sharpshooter into the ground in spokes away from the hole creating cracks for roots to find later.

Here is a good reference on how to plant a tree. Howard Garret is very well respected in the Dallas, Texas area. I'm clearly violating the amendments part but it's working for me in my clay-dominated yard.

https://www.dirtdoctor.com/garden/How-to-Plant-Trees-Properly_vq1600.htm

Here's a similar one:

https://s3.wp.wsu.edu/uploads/sites/403/2015/03/Planting-fact-sheet.pdf

it's working for me

Actually as it mentions at your link your trees are growing despite your preparations rather than because of them. With it being the case that if every amended planting hole killed woody plants outright the practice would have been dropped a long time ago. With instead it continuing to be concluded by many - including yourself - that because specific random plants in amended holes were able to grow and establish they were helped by the amending.

University level organized tests using large numbers of like plants with common shared cultivation histories including percentages operating as untreated control blocks were showing more growth being produced by untreated planting holes decades ago. With differing test plot soil types - including clays - producing the same basic outcomes.

Ariel,

My 3 and 4 foot loquats are blooming. But they were grafted trees. You will need a ten to 15 gallon pot eventually. It will need to be protected from hard freezing since it is in a pot. My guess is it has some type of fungus. It will need a bigger pot pretty soon. I would wait until spring. Do not want to plant in a big pot that can cause root rot until plant is big enough to fill the pot.

I had one growing in a 5 gallon bucket that got about 4 foot tall. It blew over after every small wind until the roots escaped the holes on the side of the bucket. Then it took a very hard wind and loosen the soil in the pot. I planted it in the ground after that.

It will need a well drained potting mix but I would put in something like lava rock to give it weight to keep it from blowing over. Maybe 10% of the mix. Your plant grew well for a first year plant. I have one I grew from seed this year and it is not quite as big as yours. I checked and the older leaves have holes but not the brown spots like yours.

Gary, if you are from Beaumont, Texas, I'm just east of you in the Orange area. All of my loquats are seed grown. The two that failed were the first one I had that did great until we had a very wet year and it was apparently borderline low and the wet year did it in. The other is still alive but is just maintaining it's height....I think it's too dry and I think the ground is also too hard there. I have another in a raised planter and its looking great but the two hurricanes blew it over each time. I may have to violate another tree planting guideline and add some guy wires to hold it up for a few years. When young, the roots seem to only be like fine hair with few to no larger diameter roots to keep it upright. The good news is that when the tree falls over, nothing breaks so you just prop it back up.

John,

I was in Beaumont but after getting over 8 feet of water in my house from Harvey I moved to Buna.

I had a couple of trees blow over due to Laura and Delta. I just drove a T post about a foot away from tree and used a bungee cord to straighten the trees. That way the tree would still move some and could build up the roots. After about 6 months the bungee cord deteriorates but by that time hopefully the tree has recovered.

Maybe next spring we can meet up somewhere and I can trade you some loquat seeds. I have a couple of improved varieties.