DISEASES AND INSECT PESTS 47 



CHAPTER XII 

 DISEASES AND INSECT PESTS 



THERE is very much in the old-time advice, " Grow your 

 plants clean," for a very large proportion of Orchid diseases 

 and insect pests are due to errors in cultivation, more 

 especially in the regulation of the temperature and the 

 ventilation. Insanitary houses lower the vitality of the 

 plants, and vegetation, like human beings, is a prey to 

 disease when kept in unhealthy conditions. 



Spot, or Orchid disease, exhibits itself in various forms. 

 It is caused, as scientists say, by different micro-organisms, 

 but in effect it is practically the same whether in the form 

 known as " Spot," often seen in Phalaenopsis, Aerides, and 

 Vandas, or in the decayed and blackened pseudo-bulbs 

 of Cattleyas, especially C. Warscewiczii (gigas), which 

 from an apparently healthy plant may develop a diseased 

 condition of the pseudo-bulbs, and become useless in a few 

 days. In all such diseases it will be seen that the tissues 

 have collapsed, the result being brown or blackish spots 

 on leaves or bulbs. Imperfect nutrition from lack of 

 healthy roots is a frequent cause of this mischief, for 

 Aerides and Vandas which have been affected with " Spot " 

 recover in the new growth, for a time at least, if a satis- 

 factory root action can be set up. 



Propagation, by freeing the recently made parts of the 

 plants from the old and worn-out back portions, which are 

 not furnished with the roots necessary to support themselves 



