Dwarf Mistletoe on Limber Pine

Dwarf mistletoe and white pine blister rust are two diseases of concern at Craters of the Moon. Both affect limber pine, which account for over 95 percent of the forested acres in the monument. Dwarf mistletoe (Arceuthobium spp.) is a native infectious parasitic organism that establishes itself on hosts such as limber pine trees. Dwarf mistletoe can reduces the vigor and growth of infected trees by appropriating water and nutrients, and disturbing the normal physiological processes of the tree. Heavy dwarf mistletoe infections increase the susceptibility of the trees to attacks by bark beetles and to other environmental stresses. In some cases, it may kill the tree by slowly robbing it of food and water. Death occurs slowly in most cases and depends on the severity of infection and on the vigor and size of the tree. Control efforts in the 1960’s resulted in the removal of 6,000 limber pine trees but were still unsuccessful in eliminating the disease. Today, dwarf mistletoe is recognized as a natural parasitic organism that has been a part of the Craters of the Moon limber pine ecology for thousands of years. It is an issue of “which is worse, the disease or the cure?”

A bigger concern is white pine blister rust. White pine blister rust is caused by an exotic fungus, Cronartium ribicola. This organism was introduced from Europe in the early 20th Century, and has spread throughout the entire range of white pines in North America. The life cycle takes three to six years to complete and attacks five-needled pines and currant shrubs in the genus Ribes. Since blister rust is an introduced species, genetic resistance of native limber pine is limited and the mortality rate has been extremely high. On average, over a third of the limber pine in the northern Rocky Mountains have been killed by blister rust, and about 75 percent of the remaining live trees are infected with it. Blister rust incidence in limber pine stands extends into central Idaho.

In the summer of 2006, the first white pine blister rust infected limber pine trees were found within the Monument. While the infected trees appears to be small in number and isolated, National Park Service personnel are surveying other limber pine stands at Craters of the Moon for the presence of white pine blister rust. Monitoring may enable resource managers to detect, monitor, manage, and hopefully eradicate white pine blister rust, as it is found. Protection of limber pine through early rust detection and immediate action is key to preserving the unique role of limber pine to the scenery and ecology of the Monument.