Disease Note

Exotic Pines Infected by Two Dwarf Mistletoes in Southern California. R. F. Scharpf, USDA Forest Service, Pacific Southwest Forest and Range Experiment Station, Berkeley, CA 94704. F. G. Hawksworth, USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Ft. Collins, CO 80526. Plant Dis. 70:173. Accepted for publication 9 October 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-173e.

Exotic pines are often planted as ornamentals in the western United States. Three species, Pinus halepensis Mill., P. pinea L., and P. thunbergiana Franco, became parasitized by dwarf mistletoe (Arceuthobium occidentale Engelm.) when planted near native P. sabiniana Dougl. infected with dwarf mistletoe. P. halepensis was also infected by A. campylopodum Engelm. when planted near infected P. ponderosa Laws. P. halepensis and P. pinea are favorable hosts for A. occidentale. Many infections with abundant shoots and fruit indicated a compatible host-parasite relationship. Growth of the parasite was poor on P. thunbergiana, however. Host-parasite compatibility of A. campylopodum on P. halepensis was not determined. Caution should be used in planting introduced pines near infected native pines.