Figure 5. The Hawksworth six-class dwarf mistletoe rating system

Note: for coastal western hemlock, a descriptor for stem swellings can be added after the numerical rating using:

N = minor stem swelling (25% of the stem circumference affected)
M = major stem swelling (>25% of the stem circumference affected).

Only a major stem swelling is recorded if there are both major and minor swellings.

For example, a hemlock with a mistletoe rating of 4 and one or more major stem infections would be coded 4M.

On a tree or stand basis, light infection is a rating of 1 to 2; moderate is 3 to 4; and severe is 5 to 6. For a stand, the rating is calculated as the average rating of all infected trees. Incidence is the percentage of susceptible trees infected by dwarf mistletoe.