Dwarf Mistletoe Quick Facts: Dwarf Mistletoe affects Lodgepole and Ponderosa Pine trees and definitely is prevalent in Hilldale Pines at this time and is spreading. This disease spreads in August, so all affected trees must be pruned or cut down prior to then. The ultimate effect of dwarf mistletoe is premature death of the affected tree and all trees around if not caught early. All effected trees are highly susceptible to bark pine beetles and fire. Description: Small, leafless, parasite flowering plants. Ponderosa Pine: Orange with thick shoots from 3-6 inches long. Lodgepole Pine: Green or Yellow, with slender shoots about 2-4 inches long. The "roots" of the dwarf mistletoe are imbedded in the bark and phloem of the tree. The parasite produces secondary root-like structures called "sinkers" that become embedded deeper in the wood as the twig adds its annual growth rings. These "roots" provide the parasite with nutrients obtained from the living tissues of the host.
Dwarf Mistletoe
Spread of Disease: The plants are either male or female, but only the females produce seeds that spread the disease. Seeds are produced in the berry and when enough pressure is built up, usually in August, the berries are broken away from their stems and the seeds are shot out an they take off at 60 miles/hour and travel average distances of 20-30 feet. They stick to whatever they hit because of a sticky coating on the seeds. The seeds landing on pine needles work their way into the twig to swell up. This takes about 2 years; then in another 2 years shoots start to appear: and within 2 more year, a cycle starts again. (6 year cycle). First 2 years - germinate and infect
Next 2 years - sprout shoots
Next 2 years - full fledged fruiting begins
A - Male Plant
B - Female Plant
C - Fruit
Signs of Infestation: A. Slight swelling of the bark at the site of infection
B. Plant growth appears on the branches and growth declines in the tops of the trees
C. Clumping of the branches of a distorted branching habit called "Witches Broom"
How Mistletoe Kills: They weaken pines by slowly robbing them of both water and food so they can't feed themselves. This occurs, because the parasite absorbs the nutrients from the tree, starting at the top. The tree dies from the top and eventually there are not enough live branches and the entire tree dies. The Mistletoes weaken pines by slowly robbing them of both water and food
Infected trees start declining in their tops as the infected branches below take more and more food. The tree slowly dies from the top. Eventually, there are not enough live branches… …and the entire tree dies. Control: Trees severely infected in the upper branches or those with only a few live branches should be cut down. Trees with high, unreachable mistletoe infections should be cut since they will continue to rain seeds on nearby trees if not cut down Lightly infected trees can be freed from the parasite by pruning off all infected branches. All branches to be pruned should be cut off flush with the trunk. The entire branch should be removed. The trees should be examined every tow or three years and any infected branches pruned off. However, if the mistletoe on a branch is close to the trunk the infection may have already entered the trunk. Shoots will form on the trunk even if the branch is removed. When pruning infected limbs, the following guidelines should be used to insure the trunk is free from infections or branches closer than indicated should be cut down to remove a future source of reinfection. Pruning Guidelines: Branch diameter at trunk: Minimum distance from trunk to shoots Under 1 inch 6 inches
1-2 inches 8 inches
2-3 inches 10 inches
3-4 inches 12 inches
The mistletoe shoots die as soon as the tree or tree branch is cut, consequently burning or covering branches is not necessary. In some cases a highly desirable tree with a trunk infection cannot be removed for aesthetic or other reasons. In these instances, the mistletoe shoots must be knocked off periodically as they appear to prevent further spread. In heavily infested areas, nonsusceptible trees can be planted to replace cut trees. Ponderosa Pine areas can be replanted to:
White fir
Blue Spruce
Pinyon pine
Limber pine
Rocky Mountain juniper
Lodgepole Pine areas can be replanted to:
Englemann spruce
Subalpine fir
Hardwood, such as birch and aspen, also can be planted in affected areas because dwarf mistletoes do not attack hardwood trees.