148 FUMIGATION METHODS 



packed, but laid loosely upon trays in the fumigating 

 box or room. The details of making and handling 

 the gas are the same as that for nursery stock and 

 greenhouse work. The apparatus to be used will 

 depend upon the number of plants grown and handled 

 annually. A convenient box for fumigating straw- 

 berry plants is shown in Fig. 71. 



Experimental and practical tests. At the Dela- 

 ware Experiment Station a very complete series of 

 tests were started by Prof. G. Harold Powell and 

 completed by Prof. K. Dwight Sanderson. Several 

 infested plants were fumigated and placed in paper 

 bags, where they were left and examined twelve hours 

 later. The following amounts of cyanide were found 

 sufficient for the destruction of the root-louse: One- 

 tenth gramme (o. i) per cubic foot space, exposed 

 twenty minutes; fifteen-hundredths (0.15) gramme for 

 fifteen minutes; two- tenths (0.2) gramme for ten min- 

 utes; three-tenths (0.3) gramme for five minutes. In 

 the same series where 0.3 gramme cyanide was used, 

 all the lice were killed where the exposure was only 

 five minutes. It is not desirable to use these larger 

 amounts even for a short exposure. The work by 

 Professors Powell and Sanderson corroborates the vari- 

 ous tests of the writer that the two- tenths gramme 

 formula is satisfactory when properly handled. Under 

 some circumstances a few lice may be secreted among 

 the crown leaves and possibly escape where large num- 

 bers of plants are fumigated. This danger can be 

 overcome largely by loose packing before fumigation. 



Practical tests. Karly in April Professor Sanderson 



