138 THE CULTIVATED EVERGREENS 



This plant-louse rarely causes enough injury to spruce to 

 make remedial measures necessary. The methods suggested 

 for the control of the spruce gall aphid would be equally 

 applicable to the present species. On larches the aphids may 

 be killed by spraying with kerosene emulsion. In the case of 

 young trees it might be advisable to fumigate them before 

 planting out. 



DISEASES AND INJURIES OF ORNAMENTAL CONIFERS.— Dickson 

 Trees, like all other living organisms, are liable to suffer 

 from numerous diseases and injuries throughout their life, 

 from the time the seeds germinate. Some of these tend to 

 reduce the vigor of the trees or to open the way for more 

 serious maladies; others depreciate their value from a com- 

 mercial or ornamental standpoint; while others kill them out- 

 right. In the forests, diseases cause an inestimable annual 

 loss, due to the ideal conditions for their spreading; but 

 individual conifers, as employed for ornamental planting, are 

 usually fairly healthy as far as actual diseases are concerned. 

 The commonest troubles of such trees are often directly trace- 

 able to environmental factors. It should always be borne in 

 mind that trees require care and attention, for when growing 

 under unfavorable conditions they will not thrive and are 

 much more subject to disease than when planted in a favorable 

 environment. 



Trees require a considerable amount of water and food. 

 These factors are naturally cared for in the forest by the 

 covering vegetation of the forest floor and the accumulation 

 of fallen leaves and debris which is continually adding to the 

 nutritive contents of the soil. On lawns and in parks, however, 

 such materials are constantly removed for various reasons and 

 it often becomes necessary to compensate for this loss of 



