It depends how old it is. If you must do it do it when it is dormant.
it could
You dig a hole and put the plum tree into it.
It may be aphids.https://www.gardeningknowhow.com/edible/fruits/plum/common-plum-tree-pests.htm
In a plum tree.
spraying a plum tree with what? against what pest/disease?
No.
Yes, but there is no guarantee tou will get a tree with worthwhile plums.
A Plum tree.
It is possible but it would be a waste of your time.
Mow the grass regularly around your plum tree.
Pine tree, pear tree, peach tree, pawpaw tree, poplar tree, plum tree.
no it is not