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.