696 A NATIONAL PLAN FOR AMERICAN FORESTRY 



after interest charges have accumulated on it for half a century may 

 make the difference between profit and loss on the plantation. At 

 many nurseries there are occasional disease epidemics which prac- 

 tically destroy entire blocks of beds and introduce a troublesome 

 uncertainty into the raising of planting stock and in planting programs. 

 Because .this uncertainty feature is one of the most serious effects of 

 nursery diseases, and since its effect cannot be expressed in dollars 

 and cents, no quantitative estimate of the total loss due to disease 

 can be made. Another consequence of diseases in the nursery which 

 is hard to evaluate, but which may prove more important than all 

 others, is the introduction of disease into new plantations on the 

 planting stock. 



Some of the heaviest losses have been due to nonparasitic diseases, 

 particularly drought, excessive heat of the soil surface, frost and 

 winterkilling, and from unwise use of mulches or fertilizers. All of 

 these are reasonably easy to prevent when recognized, and prove 

 troublesome chiefly because they are often confused with parasitic 

 diseases. Education and increasing experience of the nurserymen 

 have already resulted in reducing loss from these sources, and they 

 should not be serious in the future. 



Diseases due to parasitic fungi include the "damping off " of very 

 young seedlings, root rot of older stock, needle diseases, molds that 

 work under snow cover, and the stem rusts of pines. Damping off 

 has been found to yield to inexpensive methods of soil disinfection or 

 acidification in most places, needle diseases and fungi under snow can 

 be prevented by spraying and supplementary practices, and rust in- 

 fections can be minimized by eliminating infection sources from the 

 vicinity. Root rots are the only major group of nursery diseases for 

 which no reasonably effective control methods are known. A number 

 of alternative treatments are available for trial on nursery diseases 

 which would be too expensive for use in field plantations or natural 

 reproduction. Some diseases will probably always be found too diffi- 

 cult or too expensive to control at all nurseries or on all tree species; 

 but the nursery industry requires relatively little ground, and at the 

 worst it can hunt for sites on which a susceptible species is found 

 least subject to infection. The development of a new treatment or 

 the finding of the best nursery site for raising a particular species 

 usually requires years of experimentation, but if adequate research is 

 maintained, reforestation plans need not be retarded for fear of 

 diseases of conifers in the nurseries, at least so far as native diseases 

 are concerned. With hardwoods there has been less experience, but 

 no disease is expected for which a few years of investigation would 

 not develop satisfactory control on the more favorable nursery sites. 



DISEASES AFFECTING PLANTATIONS 



Diseases in plantations have been less studied than in nurseries. 

 Plantations, if on properly chosen sites, ordinarily suffer less from 

 disease during their first few years than do nurseries. There are, 

 however, exceptions to this rule among the diseases already studied. 

 For example, the brown-spot needle disease in the longleaf pine of 

 the Gulf States becomes important very early, even in well-placed 

 plantations. In much of the longleaf region this disease attacks the 

 trees during the first few years after planting and so weakens them 



