DISEASES AND INSECT PESTS Ay 
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, Aérides, 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 
Aérides 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 
