INSECT ENEMIES AND THEIR CONTROL 



107 



wire on which we could build the smudge and pass it up 

 into the box through the second piece of pipe. The 

 dimensions of the pipe were 4 feet long and 7 inches in 

 diameter. The smoke was thus cooled somewhat before 

 it came in contact with the lettuce. The exposure as 

 before was 15 minutes. When the box was raised the 

 temperature was 90 degrees, being 15 degrees lower than 

 in the previous trial. The leaves were not injured nearly 

 as much, but in the same manner, indicating that the 

 injury was proportional to the amount of heat accom- 

 panying the smudge. This injury occurs rarely in 

 practice." 



A practical grower has observed that lettuce is easily 

 injured by tobacco fumigation at a temperature of 60 

 degrees, that light treat- 

 ments may be made at 55 de- 

 grees without injury, that 

 strong fumigations may oc- 

 cur at 50 degrees without 

 injury, and that it is almost 

 impossible to damage the 

 crop at a temperature of 45 

 degrees. 



The danger of injury will 

 be very much less if the 

 plants are dry during the 

 smudging. It is necessary, 

 of course, to have the house 

 well filled with the smudge 

 in order to make the treat- 

 ment fully efficacious. 



The stems are sometimes 

 placed on the walks, but it 

 is better to put them in 



kettles, Cans, wire Cages Or Fig. 34. Garbage can suspended to 



other metal utensils. Some Jjjjo stems. in fumigating with t0 ' 



