24 



BULLETIN 1112, U. S. DEPARTMENT OF AGEICULTUEE. 



of the total number of black jacks on the Tusayan plot in 1909 were 

 killed by mistletoe alone or in conjunction with other agents, mainly 

 insects. While this figure itself is not high, it is alarming because 

 the indications are that the death rate vv^ill increase from year to 

 year, and although an effort was made to have all heavily infected 

 trees removed when this area was marked for cutting, it is evident 

 that mistletoe did not receive the attention which it deserved. 



Table 17. 



-Classification of dead trees on permanent sample plots of 456 acres on the 

 Tusayan and 135 acres on the Coconino National Forest. 





Per cent of dead trees, 1909-1914 (based 

 on total number of trees which died 

 during 5-year period). 



Cause of death. 



456-acre plot^ Tu- 

 sayan National 

 Forest. 



135-acre plot, Coco- 

 nino National 

 Forest. 





Black 

 jack. 



Yellow 

 pine. 



Black 

 jack. 



Yellow 

 pine. 





Per cent. 



26.4 



35.0 



5.5 



1.4 



.4 



31.3 



Per cent. 



Per cent. 



7.5 



Per cent. 

 7.9 



Mistletoe and insects 



4.8 



20.2 



Mistletoe and porcupine 







Mistletoe and suppression 









Mistletoe, porcupine, and insects 









All other causes 



95.2 



92.5 



71.9 







Total 



100.0 



100.0 



100.0 



100.0 







Weir ^ has noted the same direct relation between mistletoe infec- 

 tion and insect infestation in the Northwest, especially with Dendroc- 

 tonus valens. The origin of numerous insect infestations has been 

 traced to stands of western yellow pine heavily infected with mis- 

 tletoe. 



The main difference between mistletoe and insect injury is in the 

 length of time required for the injury to become manifest. A 

 sporadic insect infestation may develop rapidly. and may kill a large 

 number of trees in a relatively short time, and it may even continue 

 to increase until it is overcome and reduced to normal proportions 

 through some natural agency. Mistletoe, on the other hand, de- 

 velops slowly but continuously and persistently. The bark beetles, 

 when attracted by the resinuous exudations of the mistletoe-infected 

 trees, may materially hasten the death of the host which has already 

 been weakened by the parasitic mistletoe. Trees dead or dying from 

 mistletoe infection have been found infected with species of secondary 

 bark beetles and borers, such as Ips, Pityophthorus, Chrysobothris, 

 and Melanophila. 



Three black-jack saplings under 4 inches in diameter breast high on 

 one of the intensive mistletoe-study plots died during the five-year 



* Weir, James R., Mistletoe Injury to Conifers in the Northwest. U. S. Dept. Agri. Bulletin 360, 39 pp., 

 1916. 



