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Dwarf Mistletoe - Prevention and Control


What Trees are Attacked?:

Trees favored by dwarf mistletoe (Arceuthobium sp.) are certain conifers, mainly black spruce and lodgepole pine. Dwarf mistletoe infests significant stands of black spruce in the northern U.S. and lodgepole pine in the Northwest and Rocky Mountains. This mistletoe is the most damaging disease agent in lodgepole pine, causing severe growth loss and increased tree mortality. It is estimated to infest 15 percent of all black spruce stands in the northcentral states.

How are Trees Killed?:

The mistletoe plant, a parasitic member of the genus Arceuthobium , has an endophytic rootlike system that absorbs nutrients from within the host tree tissues. Its reproductive system is made of aerial shoots that rise from the host branch.
The parasite causes a wild growth called witch's brooms and spreads through the crown. Tree growth slows, eventually the crown dies and then the tree. Insects, particularly secondary bark beetles, frequently invade heavily infected trees and kill them.

How Can You ID the Disease?:

When you see a susceptable coniferous tree species with a distorted, cankered trunk and with abnormal witch's brooms you will find the fruit very easily. Dwarf mistletoe is a parasitic seed plant. On the host tree's stem and branches, it produces slender, leafless, jointed shoots which are olive-green to yellow in color. The principal function of these shoots is reproduction.

Prevention and Control:

Maintaining dense stands of trees causes dwarf mistletoe to spread more slowly and causes less damage in dense stands than in open stands. Brooms within dense stands are usually smaller and less vigorous and the mistletoe produces fewer seeds.
Clearcutting is the best way to control dwarf mistletoe in mature open stands of lodgepole pine. All infected trees should be cut, or the sanitation value of the operation will be lost.

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