Lodgepole pine dwarf mistletoe (Arceuthobium americanum)

Last Review/Updated: January 6, 2003

Lodgepole pine dwarf mistletoe (Arceuthobium americanum Nutt.) is a parasitic flowering plant that penetrates its host tree and interrupts the normal growth and function of the branch or stem. Dwarf mistletoe is one of the most serious diseases to infect, damage and kill merchantable lodgepole pine and jack pine.

Primary Hosts and Distribution

  • Lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.)
  • Jack pine (P. banksiana Lamb)

It can be found in all forest regions in Alberta.

Disease Cycle

The dwarf mistletoe disease cycle takes about 5-6 years to complete.

Dwarf mistletoe seeds that have overwintered on the host needles and twigs germinate in early summer and penetrate the host by late summer. By the second year, the mistletoe causes visible swelling of the twigs and brooming of the branches. About 3-5 years after infection, aerial shoots develop on broomed branches and produce flowers about 1-2 years later in late spring. After pollination and fertilization occurs, the female plants produce clumps of green oval berries. By mid-August to mid-September of the following year, the berries mature and seeds are actively discharged, settling onto host needles and twigs.

Detection and Damage


Look for the following signs and symptoms:

  • Profuse and distorted branching (witches' brooms)
  • Twisted, spindle-shaped swellings on branches.
  • Greenish-yellow aerial shoots of the mistletoe with tiny scale-like leaves, growing on the affected stems or branches;
  • Basal cups (shoot bases), which remain attached to the branches when the shoots disintegrate.

Very large brooms may break off, causing hazardous conditions in campground and recreation areas. Branch swellings can physically affect the quality of the wood. When dwarf mistletoe is severe, trees lose vigor, have retarded growth and may eventually die. Dwarf mistletoe can cause significant tree mortality in jack pine stands and to a lesser degree in lodgepole pine stands in Alberta.

Management

Management of the mistletoe can be successful given that infected trees can be easily detected, seed dispersal is limited, and time is needed to build up to epidemic population levels. For information on dwarf mistletoe resource material, click here. Some common management procedures used to control the spread of mistletoe include:

  • Monitoring stands;
  • Felling or burning all susceptible trees in infected stands (clear-cutting method). Infected trees should never be left in areas of stand regeneration;
  • Felling infected trees in stands (sanitation thinning);
  • Including the whole infected stand when designing cut blocks, where possible;
  • Leaving a 30 m buffer of either non-host species or a physical barrier between the regeneration and infected stands;
  • Prioritizing and harvesting infected stands in a systematic fashion;
  • Avoiding selective logging or 2-pass logging in infected stands;
  • Planting resistant non-pine species like spruce, balsam fir and aspen;
  • In non-commercial stands, removing infected branches to slow the spread of the disease. Pruning of mistletoe brooms in the early stages can also help trees regain satisfactory growth (i.e. can save the stand if the treatment is cost effective.)