Diseases and the Forest 



445 



through naturally occurring lower dead 

 branches and it results in an average 

 loss of about one-fourth of the total 

 timber volume. It rarely enters through 

 branches less than an inch in diameter, 

 however. Control of the disease is pos- 

 sible either by pruning off the lower 

 branches before they die or by growing 

 the trees so closely together that the 

 lower branches are shaded out before 

 they become large enough to support 

 the fungus. 



Fire wounds are important places of 

 entry for decay fungi, and the preven- 

 tion of fire in the woods therefore is 

 an effective indirect means of reduc- 

 ing losses from timber decays. 



Other indirect methods involve the 

 proper timing of cutting, the control 

 of stand composition to give mixtures 

 of tree species instead of pure stands, 

 and the development and use of dis- 

 ease-resistant varieties. 



VARIETIES RESISTANT to disease have 

 been successful in field and fruit crops; 

 there is every reason to expect that 

 they should prove equally valuable in 

 our future forest- and shade-tree plant- 

 ings. Although work along this line 

 has scarcely more than begun, an 

 American elm resistant to the Dutch 

 elm disease and others resistant to 

 phloem necrosis, strains of mimosa 

 resistant to the mimosa wilt, and white 

 pine resistant to blister rust have been 

 selected and tested. These resistant 

 trees are now being propagated and 

 soon will be available. Although the 

 use of resistant varieties will not save 

 the present susceptible stands of trees, 

 it does offer a promise of future safety 

 in their replacement. 



The prevention of deterioration, 

 such as from stain and decay, in forest 

 products is an effective way of extend- 

 ing our national timber supply. It re- 

 quires different methods from those 

 that can be used on living trees. The 

 young-growth timber now coming into 

 use is less resistant to decay than the 

 wood from the older stands. Modern 

 chemical treatments and more careful 

 drying and storage practices make it 



possible to avoid damage to lumber, 

 logs, pulpwood, and similar products, 

 however, and are lengthening the use- 

 ful life of posts, poles, railway ties, and 

 other wood used in contact with the 

 ground. The prompt salvage of timber 

 that is killed by fire, insects, and dis- 

 ease is saving for use much timber that 

 was formerly left to rot. 



IN BUILDINGS AND OTHER CONSTRUC- 

 TION,, the chances of decay is reduced 

 by drainage of sites, use of seasoned 

 lumber, elimination of direct contacts 

 of wood with soil, care to keep rain 

 from entering joints, ventilation or soil 

 coverage under basementless houses, 

 the judicious placing of vapor seals, 

 and the use of preservatives. 



With the ever-quickening disap- 

 pearance of accessible stands of old- 

 growth timber and with world-wide 

 timber shortages brought on by war, 

 the importance of disease in its effect 

 on the future timber crop is rapidly 

 increasing. Losses that formerly passed 

 almost unnoticed can no longer be 

 tolerated from the standpoint of 

 solvency of the timber owner no less 

 than from the public interest. We must 

 be able to grow good wood and grow 

 it profitably. That can be done only if 

 disease losses are held to a reasonable 

 minimum. 



The field to be covered by the 

 specialist in forest diseases is immense. 

 More than 100 tree species of commer- 

 cial importance occur in the forests of 

 the United States; each presents an 

 individual disease problem. When ac- 

 count is taken of the fact that our 

 forest industry ranks fourth in impor- 

 tance in the Nation, the investigative 

 effort devoted to diseases affecting 

 this resource up to the present does 

 not seem proportionate to the values at 

 stake. 



L. M. HUTCHINS is head patholo- 

 gist in charge of the Division of Forest 

 Pathology, Bureau of Plant Industry, 

 Soils, and Agricultural Engineering. 

 He is known for his extensive investi- 

 gations of virus diseases of trees. 



