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Dwarf Mistletoe

Arceuthobium spp. (parasitic plant)

64 host plants

Last updated

Data Coverage 3 of 6 dimensions
Causal Agent
Host Plants
Symptoms
Management
GDD Threshold
Regional Notes

You'll spot dwarf mistletoe as small yellowish-green plants growing in clusters directly on branches, typically 0.75 to 4 inches tall. The real giveaway is the witches' brooms: dense clumps of stunted shoots or, in western larch, scattered aerial stems that emerge from a single internal infection point. These unusual growths become obvious in late spring and summer as branches swell slightly where the parasite roots into the wood. This pathogen occurs on western hemlock and true firs at higher elevations in cool forests, though it rarely appears at lower elevations in maritime regions.

Dwarf mistletoe is a parasitic plant, not a fungus, which makes it particularly stubborn to manage. It weakens branches and eventually kills them, opening the tree to secondary decay. The parasite spreads via explosive seed dispersal in fall, with moisture washing seeds onto needles and new shoots below. Once established, it can take 2 to 5 years before visible symptoms appear. Your best option is removal: prune out infected branches entirely by midsummer when the yellow-green plants are easiest to spot. Removing just the aerial shoots won't work since the parasite will regrow from its internal infection point.

Quick Reference

Causal Agent
Arceuthobium spp. (parasitic plant)
Host Plants
64

Management

Cultural Controls

  • Remove all plants by harvesting or pruning.
  • This is easiest in mid- or late summer when plants are most easily seen.
  • Aerial shoots will re-grow unless the entire host branch is removed.
  • Forestry:Clear-cut severely infected stands.Remove infested overstory if a manageable susceptible understory is present.Favor non-hosts in mixed stands.
  • References Hawksworth, F.W. and Wiens, D. 1996.
  • Dwarf Mistletoes: Biology, Pathology and Systematics.

Host Plants (64)

Agathis australis Kauri Tāne Mahuta, Kauri Pine Araucaria araucana Monkey Puzzle Tree, Chilean Pine Araucaria bidwillii Bunya Pine Araucaria cunninghamii Hoop Pine, Moreton Bay Pine Araucaria heterophylla Norfolk Island Pine Athrotaxis laxifolia Tasmanian Pencil Pine, Summit Cedar Cephalotaxus harringtonia Japanese Plum Yew, Cow's Tail Pine Glyptostrobus pensilis Chinese Swamp Cypress, Water Pine Water Fir Shui song Larix decidua European Larch Larix gmelinii Dahurian Larch Larix kaempferi Japanese Larch Larix laricina Tamarack, Eastern Larch, American Larch Larix occidentalis Western Larch, Western Tamarack Larix russica Siberian Larch, Russian Larch Microcachrys tetragona Creeping Pine, Creeping Strawberry Pine Pinus albicaulis Whitebark Pine, Scrub Pine, White Pine Pinus aristata Bristlecone Pine, Rocky Mountain Bristlecone Interior Bristlecone Pinus attenuata Knobcone Pine Pinus banksiana Jack Pine, Scrub Pine, Banksian Pine, Hudson Bay Pine Pinus bungeana Lacebark Pine, Whitebark Pine, Baipi Song Pinus canariensis Canary Island Pine Pinus cembra Swiss Stone Pine Pinus contorta Lodgepole Pine Pinus contorta var. contorta Shore Pine Pinus contorta var. latifolia Rocky Mountain Lodgepole Pine Pinus coulteri Coulter Pine, Bigcone Pine Pinus densiflora Japanese Red Pine Pinus edulis Pinyon Pine, Piñón Pine, Two-needle Pinyon Colorado Pinyon Pinus elliottii Slash Pine, Swamp Pine Pinus flexilis Limber Pine, Rocky Mountain White Pine Pinus halepensis Aleppo Pine, Jerusalem Pine Pinus heldreichii Bosnian Pine, Snakeskin Pine Pinus jeffreyi Jeffrey Pine, Western Yellow Pine, Bull Pine Pinus kwangtungensis Kwangtung Pine, Guangdong Pine Pinus lambertiana Sugar Pine Pinus leucodermis Bosnian Pine Pinus monophylla Singleleaf Pinon Pine, One-leaved Pine Pinus monticola Western White Pine Pinus mugo Mugo Pine Pinus mugo var. pumilio Mugo pine, Dwarf Mugo pine Pinus nigra Austrian Pine Pinus parviflora Japanese White Pine Pinus parvifola Pinus parvifola Pinus pinaster Maritime Pine, Cluster Pine, Turpentine Pine Pinus pinea Italian Stone Pine, Umbrella Pine Pinus ponderosa Ponderosa Pine, Western Yellow Pine Pinus pumila Japanese Stone Pine, Dwarf Siberian Pine Pinus radiata Monterey Pine Pinus resinosa Red Pine Pinus sabiniana Gray Pine, Foothill Pine Pinus strobiformis Southwestern White Pine, Mexican White Pine, Chihuahua White Pine Pinus strobus Eastern White Pine Pinus sylvestris Scots Pine, Scotch Pine Pinus thunbergii Japanese Black Pine Pinus virginiana Virginia Pine, Scrub Pine, Jersey Pine Pinus wallichiana Himalayan Pine, Bhutan Pine Pinus yunnanensis Yunnan Pine Sciadopitys verticillata Japanese Umbrella Pine, Umbrella Pine Tsuga canadensis Canadian Hemlock, Eastern Hemlock Tsuga canadensis var. pendula Weeping Hemlock Tsuga diversifolia Northern Japanese Hemlock Tsuga heterophylla Western Hemlock Tsuga mertensiana Mountain Hemlock Wollemia nobilis Wollemi Pine