Christmas tree pests and weeds

An adult Balsam woolly adelgid, a major pest in the Christmas tree industry.

Fir trees are vulnerable to a number of different pests, most of which cause cosmetic damage to the trees, important in the Christmas tree industry. The Balsam woolly adelgid (Adelges picae) are small soft-bodied insects which attack the Fraser Fir. The insects appear as white, woolly spots on the tree and are fatal to the fir if left untreated. The woolly adeligid was native to central Europe where it affected the silver fir; it was introduced to the United States, where it has no known native predators, before 1900. Balsam twig aphids (Mindarus abietnus) are another type of tree pest which affects fir and spruce trees in the spring. The aphids can cause stunted growth in trees with heavy infestations rendering badly damaged trees unsellable. Other types of pests which affect Christmas tree production include spruce spider mites (Oligonychus ununguis), and rust mites (Nalepella). Other species of adelgids also infest fir trees, those include the pine bark adelgid, the Cooley spruce gall adelgid, and the Eastern spruce gall adelgid. Another serious pest are bagworms, the damage caused by the silk of bagworms can last years. Invasive insect species such as the pine shoot beetle and the gypsy moth also threaten Christmas tree crops.

A hillside devastated by sudden oak death includes species of conifer. The disease has been found at California Christmas tree farms.

Christmas trees are also vulnerable to large scale infestations from various fungal pathogens. In 2002 concern in the U.S. Pacific Northwest arose over the spread of a relatively new fungal disease called annesus root rot. The disease is spread by airborne fungal spores and was first discovered in Northwest Christmas tree farms in 1983. The plant pathogen, Phytophthora ramorum, which causes sudden oak death, is a fungi-like protist which was identified in the early 1990s. By 2002, sudden oak death had been reported along the California coast and the Oregon coast, and two species of conifer were identified as hosts of the pathogen, Douglas fir and coast redwood. Between 2003 and 2005 P. ramorum was detected in Douglas fir, grand fir, white fir and California red fir on Christmas trees in Santa Clara County, California.