Hi Tigercub,
I've never heard of a disease called plum tree wilt either unless you are saying that the tree is wilting.
When I hear of newly planted trees in distress it's usually one of three things.
If your trees look like telephone poles planted in the ground, then it's either planted too low or the mulch is piled up against the trunk and the root flare is not exposed. Take a look here.
http://www.tlcfortrees.info/planting%20depth.htm
http://hort.ifas.ufl.edu/woody/planting/nosoil.htm
http://hort.ifas.ufl.edu/woody/planting/rootballdimensions.h tm
Another reason for stressed newly planted trees is lack of water. That can be caused by the tree having been rootbound when planted. If the roots were circling, then you will need to remove about 2/3 of the soil around the rootball and, either untangle some of the outer roots and spread them out, or cut some of them and spread them out.
http://msucares.com/lawn/tree_diseases/images/rootball.gif
Watering a newly planted tree for the first year or two, depending on the weather, is important until it's established.
http://www.watersaver.org/pdfs/fall_watering_trees.pdf
If none of these is the problem, please get back to us with a new post and more informatio such as when the tree was planted, was it pot grown or balled and burlaped, where are you located.
Newt