The program seeks to provide and maintain virus-free sources of budwood for state nurseries and growers. Penn Premium trees are certified for both virus-free budwood and rootstocks. Surrounding states may also have certified virus-free trees. Growers are encouraged to take advantage of these programs. When ordering trees ask the nursery if it belongs to such a program.
Tree caliper is another measure of nursery tree quality.
The larger a tree's diameter, the less choice you will have in selecting scaffolds. Thicker trees tend to be taller, and it may be difficult to force branches low to the ground. In addition, after a larger-caliper tree is headed back, Cytospora canker may infect the large wound area, eventually resulting in the tree's death.