A NATIONAL PLAN FOR AMERICAN FORESTRY 719 



CONTROL PRACTICES 



Although the basic principles of control of forest-tree diseases are 

 fundamentally the same for all stands, the application of these prin- 

 ciples is strongly modified by the character and location of the stand 

 and the purpose which each stand serves. The necessity and eco- 

 nomic feasibility for control measures vary considerably on forest 

 lands for timber production, for recreational use, and for watershed pro- 

 tection. In any case intelligent control must be based on investiga- 

 tion of individual diseases in their relation to the stand as a whole, 

 and the many problems demanding attention are far beyond present 

 available resources for this purpose. 



Direct control of native diseases is being practiced to a considerable 

 extent in forest nurseries. In nurseries, trees are grown so closely 

 crowded and under such artificial conditions that they are extremely 

 susceptible to disease, but this same occupancy of a limited area by 

 a large amount of valuable stock makes it possible to spend relatively 

 large sums of money for direct-control measures, such as special meth- 

 ods of cultivation, soil treatment with chemicals or with steam, 

 spraying with fungicides or iron solutions and eradication of diseased 

 plants in the immediate vicinity of the nursery. Moderately satis- 

 factory control methods have been developed for the more conspicu- 

 ous nursery diseases, and new or obscure diseases should also prove 

 susceptible to control when sufficiently studied. 



Native diseases in the forest must be largely controlled by indirect 

 methods, such as the removal during cutting or thinning operations 

 of diseased trees or those in a condition to be especially susceptible 

 to disease. The expense is mainly in hand labor, so that such oper- 

 ations could be carried on very cheaply at the present time. So far 

 such efforts are largely confined to certain national forests, although 

 a few private owners are also eliminating diseased trees in thinnings 

 and final cuttings. A clause in national-forest timber sale contracts, 

 first introduced in 1911, calls for cutting diseased trees even though 

 they may be mainly or entirely unmerchantable. In California 

 where there has been the longest experience with its operation, this 

 sanitation cutting has been found to have a number of other advan- 

 tages as well as the removal of infection sources, and if any cost must 

 be charged to the disease-prevention feature it is very slight. It has 

 been found that most butt rot, which is an important item in decay 

 in conifers and the principal cause of cull in hardwood saw timber, 

 enters mainly at fire scars, with logging scars also of some importance. 

 This means that fire control and care in logging can be regarded as 

 factors in disease prevention. In plantations and managed forests, 

 disease prevalence can undoubtedly be controlled to some extent by 

 cpntroUing stand density. Unfortunately, information on the rela- 

 tion of density to disease has been determined for only a few diseases, 

 so that wide application of this principle will have to wait for addi- 

 tional knowledge. The relation is sometimes indirect; for example, 

 a high stand density can be made to help protect certain tree species 

 from rust fungi, because it tends to kill out other species of plants 

 that the rusts require as alternate hosts. 



Investigations by the Federal Government of wood-destroying 

 fungi that cause heavy losses by decaying the wood of trees of mer- 

 chantable size, have shown for the few species studied that young 

 stands are practically free from decay but with increasing age, losses 



