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Pine and fir trees, grown purposely for use as Christmas trees, are vulnerable to a wide variety of pests, weeds and diseases. Many of the conifer species cultivated face infestations and death from such pests as the balsam woolly adelgid and other adelgids. Aphids are another common insect pest. Christmas trees are also vulnerable to fungal pathogens and their resultant illnesses such as root rot, and, in the U.S. state of California, sudden oak death. Douglas-fir trees in particular are vulnerable to infections from plant pathogens such as ''R. pseudotsugae''. Larger pests also pose a threat to Christmas tree plantations and harvests. Mammals such as deer, gophers and ground squirrels are threats to Christmas tree crops because of the damage they cause to roots and buds. Certain species of birds are also considered pests, among these is the pine grosbeak which feeds on conifer buds. Herbaceous weeds, as well as woody plants, also compete with Christmas tree crops for water and nutrients and thus must be controlled by farmers. There are several methods of control, including mowing, chemical herbicide use, and tilling. ==Insects== The conifer species used and cultivated as Christmas trees are vulnerable to dozens of different pests, most of which cause cosmetic damage to the trees, important in the Christmas tree industry.〔〔''(Christmas Tree Pest Manual )'', Michigan State University Extension, ''United States Department of Agriculture'', 1997–1998, (Table of Contents ). Retrieved September 7, 2007.〕 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.〔Sidebottom, Jill R. (Frequently Asked Questions about Christmas Tree Farms and Pesticides ), Mountain Horticultural Crops Research & Extension Center, ''North Carolina State University'', October 30, 2006. Retrieved September 3, 2007.〕 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 species of adelgids also infest fir trees, those include the pine bark adelgid, the Cooley spruce gall adelgid (''Adelges cooleyi''), and the eastern spruce gall adelgid (''Adelges abietis'').〔 Another serious pest are bagworms. These pests can defoliate a tree completely if present in large enough numbers. Additionally, the damage caused by the silk of bagworms can last years.〔Day, Eric. (Insect Pests of Christmas Trees slides ), Insect Identification Laboratory, Department of Entomology, ''Virginia Tech'', January 2002. Retrieved September 3, 2007.〕 Invasive insect species such as the pine shoot beetle and the gypsy moth also threaten Christmas tree crops.〔(Division of Communications: Untitled story ), ''Outdoor Indiana'', November/December 2006, Indiana Department of Natural Resources. Retrieved September 4, 2007.〕 Gypsy moth infestations in Canada required restrictions and requirements to be placed upon Christmas tree growers with plantations in "gypsy moth regulated areas".〔 The restrictions and requirements included ongoing site monitoring, active moth eradication by the grower, accurate record keeping, and government directed moth eradication programs.〔 Failure to abide by the rules could result in revocation of the "approved grower" status from the Canadian Food Inspection Agency.〔(Gypsy Moth Control Program for Christmas Tree Growers ), Export requirements for cut Christmas trees to Mexico: D-95-11, ''Canadian Food Inspection Agency'', August 2, 2007. Retrieved September 7, 2007.〕 The major types of conifers cultivated, pines, Douglas-firs, true firs, and spruce trees, are all affected by some types of insect pests.〔 Douglas-firs are most vulnerable to the Cooley spruce gall adelgid. The true firs are most susceptible to insects such as the balsam gall midge (''Paradiplosis tumifex''), and the balsam twig aphid. Species of spruce trees face assault from insects such as the white pine weevil (''Pissodes strobi''), Cooley spruce gall adelgid, and the pine needle scale (''Chionaspis pinifoliae''). The final category of Christmas trees, pines, are commonly susceptible to insect infestation and damage from the pine root collar weevil (''Hylobius radicis''), Zimmerman pine moth (''Dioryctria zimmermani''), pine needle scale, and white pine weevil.〔McCullough, Deborah G. and Koelling, Melvin R. (Integrated Pest Management in Christmas Tree Production ), Integrated Pest Management World Textbook, ''University of Minnesota'', September 20, 1996. Retrieved September 7, 2007.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Christmas tree pests and weeds」の詳細全文を読む スポンサード リンク
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