1 68 DISEASES AND INSECT ENEMIES. 



are constantly exposed to rain and dew. Much 

 benefit may be derived, however, by shading the 

 plants in some way. Rain does not seem to give 

 as much trouble as dew. This is probably owing to 

 the fact that rain washes the spores from the 

 leaves before they have an opportunity to germin- 

 ate, while in the case of dew the moisture comes on 

 so gradually that the very best conditions are fur- 

 nished for the germination and development of the 

 fungus. A shading of laths or a screen of any kind 

 will often be sufficient to protect the plants from 

 dew, and thus in a measure ward off the spot. 

 However, it is of the highest importance that the 

 plants be under cover as soon after the middle of 

 August as possible, for wherever they are left 

 outside the danger from infection is very much 

 increased. 



Everything that has a tendency to weaken 

 the foliage must be avoided. Too much fertilizer 

 will often cause a tender growth of leaves, and 

 when in such condition spot is very apt to appear 

 if several days of warm, cloudy weather come on. 

 One of the greatest sources of injury is tobacco in 

 the form of smoke. Many growers use tobacco 

 for combating insects, but in our experience it is 

 found very dangerous and apt to cause serious 

 trouble. The nicotine in the tobacco has the 

 power of weakening the tissues to such an extent 

 that the spot fungus finds it an easy matter to 

 infect the foliage. A light fumigation seldom 



