Dwarf mistletoes are a common problem in Colorado forests on ponderosa and lodgepole pines. Nursery and ornamental plantings seldom are affected, but the parasite can be introduced to an area by planting trees infected with dwarf mistletoe.

Quick Facts:

• Ponderosa, lodgepole, limber and pinon pines and Douglas-fir are the most common trees affected by dwarf mistletoes in Colorado
• Dwarf mistletoes are host-specific, parasitic flowering plants that spread by birds that consume the seeds and by forcibly ejected seeds from the parent plant.
• Damage includes growth reduction, loss of wood quality, poor tree form, predisposition to insect infestation and diseases, premature death, and reduction of seed crops.
• Mistletoe seeds are dispersed in August and early September. Mistletoes spread slowly, typically moving through a forest at 1 to 2 feet per year in dense stands.
• Diseased trees decline and die from the top down as lower infected branches take more food and water.
• To prevent infection and help manage dwarf mistletoe, plant resistant trees, improve tree vigor, form buffer zones, prune infected branches or remove infected trees.

Symptoms
The first symptom of dwarf mistletoe infection is a slight swelling of the bark at the infection site. As the parasite's sinkers become more extensive, a distorted branching habit or witches' broom may form. Witches' brooms take years to form. They slowly take more and more food from uninfected parts of the tree. This reduces vigor and causes premature death. Yellow foliage, reduced foliage and mortality of branches or the entire top of the trees may indicate mistletoe infections are present.
The parasite is identifiable when the yellow to green or brownish-green segmented shoots protrude from the infected part of the tree. These woody shoots are 1/2 to 6 inches long and 1/8 to 1/4 inch in diameter. Shoots form two to three years after infection. Douglas-fir dwarf mistletoe shoots are hard to see because they are only about 1/2 inch long.

Management
Dwarf mistletoes are not quick killers, so long-term management options are feasible. However, dwarf mistletoe infected trees may attract various types of bark beetles that may breed and kill parts or the whole tree.

Pruning and removing trees is the best management to reduce or eliminate dwarf mistletoe infestations in ornamental trees or urban forests. First, remove severely infected trees or those with only a few live branches. Trees with high, unreachable mistletoe infections will continue to shower seeds on nearby trees if not cut down. It is not necessary to completely eradicate the mistletoe. Prune and remove a few heavily infected trees and keep a green forest on the property.
For more information on management, click on: Dwarf Mistletoe Management CSU Extension Service