I bought my kumquat tree a year ago from Costco. I planted it in my front yard. About a month or so after I planted it last year, the leaves started to curl and turn yellow and fall off. I tried solid fertilizer and then liquid fertilizer. I make sure I water the plant. I don’t know what to do. It makes me depressed looking at it. Does it have a disease? It’s been looking sick since a month after I planted it a year ago.