Forcing of Tomatoes. 



259 



ered, and the trouble no doubt was a physiological disturbance due 

 to heavy watering following a period of rapid growth, accompanied 

 by cold cloudy weather. 



Insect Enemies — Controlled by Fumigating. In common with 

 the experience of many other growers, the houses have been for 

 several years infested with white fly (Aleyrodes). This insect has 

 caused much anxiety to the grower of plants under glass, and many 

 attempts have been made to exterminate the pest by commercial 

 grower and experiment station. Spraying with soap solutions and 

 fumigating with various tobacco preparations were thoroughly 



Fig. 9. — Forcing in ground bed. 



tested in the Cornell forcing houses, but with no lasting benefit, and 

 finally fumigation with hydrocyanic acid gas was resorted to, using 

 potassium cyanide ninety-eight per cent strength, and commercial 

 sulphuric acid sixty-six per cent and a small quantity of water. 

 Many trials were made with this gas, varying the amounts of cyanide, 

 the time of exposure, the temperature and humidity of the houses. 

 In some instances, there was injury to foliage without destruc- 

 tion of the insects; and especially was this true when fumigation 

 was made in daylight, or when the houses were very damp. Short 



