My tree is very young but the leaves are curled up. I know it is a common disease, but what should I do for it?
It could be aphids affecting your plum tree resulting in the leaf curl. Neem oil should help with this and is an effective fungicide as well in case anything else pops up. Here is more information: https://www.gardeningknowhow.com/edible/fruits/plum/control-leaf-curl-plum-aphids.htm