443 



DISEASES AND THE FOREST 



L. M. HUTCHINS 



Trees, no less than other large forms 

 of life, are subject to diseases that re- 

 duce their growth, destroy their use- 

 fulness, or bring death. The threat of 

 disease is ever present, from the time 

 that a tree emerges as a seedling to the 

 end of its useful life. 



In the virgin forests this threat was 

 lessened because through centuries of 

 interaction a certain degree of natural 

 balance between the trees and their 

 disease enemies had been achieved. 

 Man, in his need for land, shelter, fuel, 

 and communication, however, upset 

 this balance by cutting, clearing, burn- 

 ing, and planting. He brought in exotic 

 tree species from foreign lands, too, 

 and otherwise so changed the forests 

 from their original, natural state that 

 over most of the country the once- 

 stabilized relations no longer exist and 

 the danger of disease has increased. 



With the new tree species or their 

 products from abroad came new dis- 

 eases, which have found here a more 

 congenial environment than in their 

 native habitats. Thus, chestnut blight 

 was brought in from Asia; white pine 

 blister rust on infected pine seedlings 

 and the Dutch elm disease and its in- 

 sect carriers on elm burl logs were 

 brought in from Europe. For our native 

 chestnut, the results have been disas- 

 trous. Our white pines have been saved 

 only by the development of an effective 

 method of control. Losses in American 

 elm from the Dutch elm disease have 

 been heavy, and the future of the spe- 

 cies is still in doubt, despite progress in 

 means of control. 



Losses from presumably native dis- 

 eases that have become epidemic are 

 also assuming serious proportions in 

 several places. A highly destructive 

 virus disease, known as phloem necro- 

 sis, has killed thousands of elms in 

 several midwestern cities. Littleleaf, a 

 disease whose cause we do not yet 

 know, is making heavy inroads into 



stands of shortleaf pine in the southern 

 Piedmont. Another disease of unde- 

 termined cause, provisionally named 

 pole blight, is spreading in second- 

 growth western white pine stands in 

 Idaho, Montana, and Washington. Al- 

 together, since the turn of the century, 

 more than 25 new forest-tree diseases, 

 introduced or apparently native, have 

 been discovered in this country. Not 

 all have proved equally important, but 

 the aggregate loss of trees from them 

 has been tremendous. 



Most of the losses, however, are not 

 from diseases of the spectacular epi- 

 demic type, but rather from the many 

 relatively inconspicuous diseases at 

 work always in our forests in and on 

 leaves, bark, wood, roots, seedlings, 

 saplings, old trees. Best estimates place 

 the annual saw-timber loss from heart 

 rots in the forests of the United States 

 at \ l /2 billion board feet. It is these 

 everyday insidious losses, as well as 

 those from the spectacular epidemic 

 diseases, that must be guarded against 

 if our forests are to continue to supply 

 the wood we need. 



Everybody knows how necessary it is 

 to protect farm and orchard crops 

 cotton, tobacco, vegetables, grains, and 

 fruits against disease. Even more im- 

 portant is the protection of forest trees, 

 which occupy the land many years be- 

 fore they are harvested. 



TREE DISEASES are of two main 

 types, parasitic and nonparasitic. The 

 parasitic or infectious diseases are 

 frequently highly contagious. They are 

 caused mainly by low forms of life, such 

 as bacteria and fungi, by viruses, by mi- 

 croscopic eel worms or the nematodes, 

 and by seed plants such as mistletoes 

 and dodders. 



Among the nonparasitic diseases are 

 such disorders as the sunscald, winter 

 injury, drought injury, root drowning 

 or suffocation, nutritional excesses and 





