206 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION. 



Fumigation. A good many experiments were carried on with a 

 view of determining the feasibility of fumigation as a means of con- 

 trolling the vine hopper. The vines were enclosed either in canvas 

 tents, or a galvanized iron tank or drum inverted over the vine, or a 

 square box made of building paper (Fig. 17). In most of the experi- 

 ments carried on the tank or box was used, since the air capacity did 

 not vary in these as was the case with the loose canvas tents, and the 

 dosage could be accurately calculated. 



One gram of cyanide of potassium to thirty cubic feet of space was 



Fig. 17. Fumigating box made of building paper, used in the experiments on 



fumigation. 



found to kill the hoppers in from five 'to ten minutes. In some cases' 

 with this dose, however, a few of the most tender leaves would be 

 slightly burned. The work was done, however, during the day time, 

 when the vine is more active and more susceptible to the gas than 

 at night. Because of the short exposure necessary to kill the hoppers 

 'd few tents would be sufficient to keep a crew of fumigators busy, so 

 that the initial expense of apparatus need not be very great. The dose 

 necessary for each vine is also small, so that there is not a large expense 

 of chemicals. The moving of the tents from vine to vine and the 

 weighing and charging of the chemicals, however, require much time 



