58 



FUMIGATION INVESTIGATIONS IN CALIFOENIA. 



drops of acid might reach the tent. The genprator cover described 

 above so deflects the gas, and incidentally such acid as is carried with 

 it, that the drops are thrown to the ground, thus saving the tents. 

 The decreased cost in mending of tents will doubtless pay for the 

 cost of such a cover device several times over in a fumigating season. 

 A third advantage, which we have not as yet demonstrated but 

 which we have reason to believe will develop, is a better distribu- 

 tion of gas through the tent. Heretofore the most difficult part of 

 the tree in which to destroy insects is the lower part. This is also 

 the part of the tree in which the purple scale is largely to be found. 

 With the open generator the gas rises straight up in a narrow column 

 for several feet (fig. 22, at left), being broken up and distributed 



through the top of the tree 

 first. As the gas is lighter 

 than air, it is not to be ex- 

 pected that it will quickly 

 become uniformly distrib- 

 uted throughout the bot- 

 tom of the tent, even if at 

 any time it becomes as con- 

 centrated here as at the top. 

 The greater burning effect 

 and better killing effect in 

 the top of the tree w^ould 

 tend to substantiate this as- 

 sumption. Field observa- 

 tions in fumigating large 

 trees show that the gas is 

 of no great strength at the 

 lower part of the tent for 

 several minutes after the 

 charge is set off. With this 

 new cover the gas is broken 

 up and distributed through the bottom of the tent first (fig. 22, at 

 right). By the time it reaches the top it is pretty generally distrib- 

 uted throughout the tent. As the bottom of the tree is the first to 

 receive the full benefit of the gas, a more complete killing of scale at 

 the bottom of the tent may be expected than with an open generator. 



AN IMPROVED SYSTEM OF FUMIGATION. 



During the month of July, 1908, a system of fumigation which has 

 decided advantages over the old method was introduced into Cali- 

 fornia field practice. In this system the tents are marked after the 

 Alorrill method, described on pages 27-30 (figs. 11 and 12). Only 

 the three parallel lines are used, the cross line being unnecessary 



Fig. 21.— a cover device attached to a fumigation generator, 

 corrugations in cover allow gas to escape. (Original.) 



