Dwarf Mistletoe
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Hagle, S.K; S. Tunnock; K.E. Gibson; and C.J. Gilligan. 1987. Field Guide to Diseases and Insect Pests of Idaho and Montana Forests. U.S. Department of Agriculture, Forest Service. State and Private Forestry, Northern Region. Missoula, Montana. Reprint 1990. Publication Number R1-89-54.
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Contents |
Hosts
Five species of dwarf mistletoe infect II native conifers in Idaho and Montana. Major hosts in this area are Douglas-fir, western larch, lodgepole pine, and ponderosa pine.
Distribution
Generally the range of host species except Douglas-fir and ponderosa pine dwarf mistletoes. Douglas-fir dwarf mistletoe occurs only west of the Continental Divide. Ponderosa pine dwarf mistletoe is found near Coeur d'Alene, Idaho.
Damage
Witches brooms often form on infected branches (figs. 76, 77). Stem cankers or swellings sometimes result from stem infections by dwarf mistletoe. Height and diameter growth reductions
Identification
Dwarf mistletoe plants form shoots on branches or stems of host trees (figs. 78, 79, 80). The shoots may be simple or branched and from 1 to 4 inches in length. They are scattered along young twigs of the host or in groups of varying numbers on branches or stems. The jointed shoots have opposite pairs of scale-like leaves. Color varies from yellow to purple to brown or olive green. When shoots are shed, small basal cups often remain embedded in the bark. Witches brooms, cankers, and swellings on stems and branches are also indicators of dwarf mistletoe infections. See Table 3 for help in identifying species of dwarf mistletoe.
Similar damages
Witches brooms, cankers, and swellings can be caused by a number of other agents. Stimulation brooms often are produced after stands have been thinned. Occasional witches brooms and swellings are caused by frost damage to growing cells in both cambium and buds. Elytroderma needle cast causes witches brooms on ponderosa pines. Cankers are caused by a number of common canker-causing fungi. Sunscald and mechanical injuries also cause damages which can be confused with cankers. Presence of dwarf mistletoe plants in damaged stands is the best assurance of dwarf mistletoe infection.
Comparison of Dwarf Mistletoes Occurring in Idaho and Montana
| Species | Principal Host | Secondary Host | Occasional or Rare Host | Shoot Lenght Mean | Shoot Lenght Max | Shoot Color | Branching |
|---|---|---|---|---|---|---|---|
| Arceuthobium americanum | Lodgepole pine | PP,WBP,LP,ES | 2.5 | 12 | Yellow or Green | V | |
| Arceuthobium campylopodum | Ponderosa pine | LPP | 3 | 5 | Brown or Green | F | |
| Arceuthobium cyanocarpum | Limber pine | WBP | WWP | 1 | 2 | Green | F |
| Arceuthobium douglasii | Douglas-fir | GF,SAF,ES | 1 | 3 | Green | F | |
| Arceuthobium laricis | Western larch | SAF, LPP | ES,WBP,PP | 1.5 | 2.5 | Dark purple | F |
Gallery
 Photo by Oscar Dooling, USDA Forest Service, Bugwood.org |
References
- Anonymous. 1982. For. Insect & disease identification and management. USDA For. Serv.,Northern Region; Idaho Dept. of Lands, Insect and Disease Control; Montana Dept. of State Lands, Division of Forestry. 192 p.
- Bega, R. V. 1978. Diseases of Pacific Coast conifers. USDA For. Serv. Ag. Hndbk. No. 521, 206 p.
- Boyce, J. S. 1961. Forest Pathology. McGraw-Hill Book Co., New York, NY. 572 p.
- Hawksworth, F. G. and O. J. Dooling. 1984. Lodgepole pine dwarf mistletoe. USDA For. Serv., For. Ins. & Dis. Leaflet 18, 11 p.
- Hepting, G. E. 1971. Diseases of forest and shade trees of the United States. USDA For. Serv. Ag. Hndbk. No. 386, 658 p.
- Kimmey, J. W. and J. L. Mielke. 1959. Western dwarf mistletoe on ponderosa pine. USDA For. Serv., For. Pest Leaflet 40, 7 p.
