86 DISEASES OF CROP-PLANTS 



time goes on and beneficial results are demonstrated this 

 disposition will increasingly prevail. 



For leaf, flower and fruit diseases of trees, the most general 

 remedies are (i) wide spacing, to secure access of air and sun ; 



(2) efficient drainage, to reduce humidity in rainy periods, and 



(3) spraying. Where the first measure conflicts, as it may, with 

 the requirements of good vegetative development, a compromise 

 has to be made. In the case of debility diseases due to the 

 effects of exposure close planting may have distinct advantages. 



Any trees which harbour pests and diseases liable to be 

 transmitted to the crop should be as far as possible eliminated 

 from the neighbourhood. 



Pruning for twig and branch diseases, and trenching for root 

 diseases are dealt with in later sections. 



There are two pieces of general counsel, of which the sound- 

 ness is beyond dispute, which may be offered in the present 

 connection to planters of permanent crops. The first is that 

 thought should be given to the possible incidence of disease in 

 laying out fields, so that, by wide and regular spacing, the pro- 

 vision of a regular drainage system, and the separation of blocks 

 by passable roads, accessibility and some degree of isolation may 

 be secured. 



The other is that arrangements should be made for steadily 

 replacing, section by section, trees which have passed their 

 prime. In the modern commercial orchard of temperate countries 

 only trees in full vigour are tolerated, and the considerations 

 are the same, if their recognition is at present less, in the West 

 Indies. One great advantage is the resistance offered by such 

 trees to pests and diseases and their greater recuperative powers 

 when injured. 



