LARCH MISTLETOE. 25 



Burls found in early life on the trunk cause suppression by reduc- 

 ing the food-transporting tissues, form open wounds for the entrance 

 of fungi and insects, and cause streaks of pitch to appear in the 

 wood, which often extend from one burl to another. Burls formed 

 at the bases of branches produce similar injuries and may also cause 

 a premature pruning of the branch. 



The extra weight of the brooms, together with the accumulated 

 debris, causes the branches to break off readily under the influence of 

 the wind and deprives the tree of its normal food supply. 



Mistletoe thrives best on trees of uneven stands. In dense, close, 

 even-aged stands, as in deep valleys, the parasite usually causes less 

 damage. 



The type of infection working the greatest injury in the shortest 

 time is the formation of brooms on the branches. 



Thinning promotes the development of the parasite in the crown ; 

 hence, all infected trees of any size, age, and condition should be 

 marked for cutting. 



The mistletoe spreads more rapidly in the crowns of younger 

 trees, owing to the greater number of twigs in close proximity sus- 

 ceptible to infection. 



Two types of infection by the mistletoe occur: (1) By the seed 

 falling on the branches, where a broom usually develops if infection 

 occurs, and (2) the gradual advance of the cortical root system of the 

 mistletoe along the branch to younger tissues. The seeds of mistletoe 

 have been known to fall on the healing tissue of wounds on old parts 

 of trees, causing infection. 



Suppression by mistletoe causes a more rapid and an earlier forma- 

 tion of heartwood in the younger age classes, thus inviting insects and 

 fungi at earlier periods of growth. 



Mistletoe may be controlled by inserting in all timber-sale con- 

 tracts a clause requiring the cutting on the sales area of all larches 

 infected with mistletoe, whether merchantable or unmerchantable. 



