JACK PINE. 21 



DISEASES.' 



Jack pine stands arc usually free of serious fungous diseases, but 

 when they reach an age of from GO to 90 years many of the trees 

 become heart-rotted. The fungus that most often causes this con- 

 dition is Polyporus sclvweinitzii, but Trametes pini is sometimes re- 

 sponsible for it. 



The most common disease in jack pine is the gall-forming rust, 

 Cronartium cerehrum (Peck) Hedge. & Long. The injury done to 

 young and old trees alike by this fungus is such that, in any system of 

 forest management of jack pine, methods for its eradication should 

 be considered. "It causes the death or early suppression of trees of 

 tender years and seriously interferes with the development of more 

 mature growth.'' * 



The defect known as ''witches' broom" is frequently present in 

 jack pine crowns, especially in open stands on dry, sandy soils. This 

 is a bushy growth of fine twigs from an affected point on a terminal 

 shoot. The stimulus for this growth is probably furnished, in most 

 cases, by some peremiial fungus. The ''witches' broom" precludes 

 further development beyond the point of attack^ and the increment 

 of a badly infected tree falls off rapidly. The damage is not wide- 

 spread, however, and in the aggregate is not serious.^ Near the limits 

 of its northern range the jack pine is subject to attacks by mistletoe, 

 resulting also in the formation of "witches' brooms." 



Several fungous saprophytes attack jack pine wood left in the for- 

 est and cause its quick decay. Dead trees usually become unsound 

 within 2 or 3 years. 



BISECTS. 



Jack pine is rarely damaged by insects, except where the stand 

 has been seriously weakened b}?^ fire, especially by fire occurring in 

 the summer. According to Dr. A. D. Hopkins, of the Bureau of 

 Entomology, United States Department of Agriculture, the living 

 jack pine is often attacked and more or less seriously injured at the 

 base and on the stems of saplings by bark w^eevils and bark beetles, 

 on the buds and twigs by tip moths, and on the foliage by saw fhes. 

 The tip moth has attacked most of the jack pine in the plantations 

 at Halsey, Nebr., reducing the height growth and causing minor 

 crooks. The bark and wood of weakened, dying, and felled trees are 

 subject to attack b}^ the common wood-boring insects, which also 

 cause pinhole and wormhole defects in the crude products.^ 



* For a full discussion of the diseases of jack pine, see Bulletin No. 212, U. S. Department of Agriculture, 

 " Observation on the Pathology of the Jack Pine," by James R. Weir, Forest Pathologist. 



2 Any evidence of serious injury to living trees or their products, kno'svn or supposed to be caused by 

 insects, should be reported to a Federal or State entomologist vnih a request for ad'vi«e as to the need of 

 adopting measures for prevention or control. 



