Development of Dwarf Mistletoe Infections on Western Hemlock in Coastal Oregon
Needles and twigs of western hemlock, Tsuga heterophylla, were inoculated with seed of Arceuthobium tsugense in October 1972, 1973, and 1974. One infection developing from the earlier inoculations produced mature seed within 4 years; however, most produced seed in the fifth year. Success of inoculation was affected by loss of seed to winter storms, fungus attack, and insect predation. Approximately two-thirds of the 4,584 seeds placed on host trees were retained over winter. Seed placed on twigs was more likely to overwinter on the host than seed placed on foliage. About 45 percent of these 3,069 overwintering seeds germinated and about 8 percent (243) caused infection of host tissues. No strong relationship existed between success of infection and branch height or aspect, nor exposure of tree crown to direct light. Forest Sci. 25:237-243.