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- 
