control problem will again become more important. When tobacco is to be 

 exported, any infestation creates a serious problem, and this problem is further 

 complicated if the tobacco is held for a relatively long period before shipment. 

 Tobacco held awaiting export is usually stored in closed-type warehouses similar to 

 those shown in figure I. It is in this type of building that fumigation is per- 

 formed if insect infestation exists. 



Insecticides and Fumigants 



In the past, dusting with pyrethrum powder was recommended by the Rich- 

 mond Stored Tobacco Insect Laboratory of the Bureau of Entomology and Plant 

 Quarantine, for the control of the tobacco moth. The Laboratory's study of 

 pyrethrum oil sprays developed a more satisfactory control. Sprays have been 

 much more effective than dusting, but fumigation, which has also been used 

 for many years, is still the most widely accepted method of control, particularly 

 against the cigarette beede. 



Several fumigants have been used in the past but at present hydrogen cyanide 

 (HCN) is probably used more extensively than any other gas. The develop- 



■ 



PMA 17727 



Figure 1. — Closed-type storage warehouses at Norfolk, Va., where a part of the 

 tobacco held under the Commodity Credit Corporation loan program is located. 



ment of Carbacryl (formerly known as Acrylon) has been studied and its use 

 tested on a commercial scale. Methyl bromide and other gases have also been 

 tested. All these fumigants have their desirable characteristics. In Circular 635 

 and other publications issued by the Bureau of Entomology and Plant Quaran- 

 tine, methods of application of these fumigants are discussed. Information as 

 to the effectiveness of these gases and sprays, and safety measures necessary in 

 their application, are also given. 



In every instance, however, the sealing of a storage building to be fumigated 

 at atmospheric pressure must be adequate. Over a period of years there has been 

 little change in the methods of sealing employed by the industry. As sealing is 

 essential to fumigation, some study of the methods and materials used in this work 

 seems desirable. 



