INSECT ENEMIES AND THEIR CONTROL 111 



regardless of whether insects can be found or not. For 

 those who have not had experience in this method of 

 fumigating, it will be safer for them to begin with light 

 treatments, note results and increase the amount of 

 cyanide if necessary and also the frequency of the appli- 

 cations. Five ounces of cyanide to 1,000 cubic feet may 

 be used when there are no crops in the houses and it is 

 desired to kill red spiders and all other animal life. 



Daylight fumigations have not been successful. It is 

 always important to attend to this operation at night, 

 when there is no wind. The workmen, too, are then out 

 of the houses and visitors are not likely to be in the 

 establishment. 



Dry plants and low humidity are exceedingly impor- 

 tant in order to avoid injury to the crops. The losses 

 sustained by those who first tried cyanide fumigation 

 were often due to excessive moisture conditions. Any 

 accumulation of moisture on the plants is certain to 

 absorb the gas and thus damage the plants, and high 

 humidity causes the gas to settle quickly to the beds and 

 walks. There should be no watering or spraying on the 

 days when the houses are to be fumigated. 



There is some difference of opinion regarding the 

 effect of the gas at different temperatures of the green- 

 houses, though most growers believe that the plants are 

 more susceptible to injury when the temperature is high. 

 There is probably little if any difference in the effect of 

 the gas at temperatures ranging from 50 to 60 degrees. 



Trials made in a tomato house at The Pennsylvania 

 State College indicate that tobacco and cyanide fumiga- 

 tions may be made to advantage at the same time. Pans 

 of tobacco powders were ignited and immediately there- 

 after the bags of cyanide, at the rate of only one-third of 

 an ounce to each 1,000 cubic feet of space, were placed in 

 the crocks. This double treatment was found to be 

 highly satisfactory in combating the white fly. It is be- 



