Arceuthobium divaricatum, a perennial stem parasite, appears on pinyon trees throughout New Mexico. Known as pinyon dwarf mistletoe, the parasite belongs to the Viscaceae family (mistletoe family). It occurs predominately on Pinus monophylla and Pinus edulis but can also occur on Pinus californiarum, Pinus discolor, Pinus quadrifolia and Pinus cembroides in parts of Colorado, Arizona, Nevada, California, Texas and Utah, according to the U.S. Forest Service.
The pinyon dwarf mistletoe parasite gradually causes the decline of its host pine trees in New Mexico and other regions of the country. The pine tree's growth is stunted and the tree looses vigor over time, which makes it more susceptible to other diseases. The parasite takes food and nutrients from the tree. A pine tree that is heavily infected with the parasite suffers extensive dead branches, which makes it unsightly and also poses a serious wildfire threat.
Despite the fact that the parasitic pinyon dwarf mistletoe slowly kills its host, the parasite does offer benefits to the environment. It helps to feed local New Mexico wildlife and birds who relish the flowers, shoots and fruits that it produces. It offers a superb hiding location and cover against inclement weather for small mammals and birds who seek refuge within the witch's brooms that the parasite produces. When the pine tree finally succumbs and dies from the heavy parasite infestation the dead tree is often utilized as a wildlife tree by cavity nesting birds or other wildlife.
From August through September the pinyon dwarf mistletoe produces profuse, tiny blossoms. Each plant is either male or female. Pollination occurs from the wind and insect activity. Approximately 13 months after pollination occurs tiny fruits are produced by the mistletoe female plants. The tiny fruit contain the seed that the plant expels with a pop through the air. A sticky residue coats the seed so it easily adheres to the pine tree that it lands on, according to the Colorado State University.
The seeds begin to produce roots on local pine trees. The specialized root-like structures wind past the tree's bark and into the very wood of the tree. Top growth of the pinyon dwarf mistletoe does not show up visually on the pine tree until the mistletoe is three to five years old but a bulge under the bark of the tree may be discernible after one to two years. Extensive damage to the tree has normally occurred within six years of infestation. The mistletoe normally effects the lower portions of the tree's canopy and then gradually works its way upward.
Control of severely infected pine tree forests in New Mexico often require clear cutting of all infected trees in the area. Lightly infested areas may only require thinning to gain control. Selective pruning of infected areas of the tree that have dwarf mistletoe infestation will also help prolong the tree's life. The parasitic dwarf mistletoe produces large witch's brooms on the tree, which severely sap the tree's nutrients and water so the area will need to be severely pruned away to extend the tree's lifespan.