48 



CIRCULAR 369, U. S. DEPT. OF AGRICULTURE 



held in closed storage, fumigation with hydrocyanic acid gas is the 

 most effective means of preventing further loss from insect attack. 

 Since the f umigants will not ordinarily penetrate tobacco hogsheads 

 in killing concentrations deeper than from 3 to 6 inches, fumigations 

 in warehouses should be timed to correspond with the emergence of 

 the broods of insects. From May to November, when tobacco insects 

 are normally abundant, it is desirable to suspend boards covered with 

 fly paper under electric lights in warehouses to serve as indicators of 

 the abundance of the insects. Whenever 50 adult cigarette beetles or 

 30 adult tobacco moths are caught on one indicator in a week it is well 

 to fumigate. 



Figure 39. — Interior of tobacco storage with tobacco stored in hogsheads. 



Two or more fumigations are usually required in one season. For 

 light to moderate infestations a dosage of 10 ounces of liquid hydro- 

 cyanic acid or its equivalent should be applied, whereas heavy in- 

 festations should receive 16 ounces per 1,000 cubic feet. The exposure 

 should be for 72 hours if this does not interfere with warehouse 

 routine. 



For the fumigation of tobacco factories a dosage of 8 ounces of 

 liquid hydrocyanic acid or its equivalent per 1,000 cubic feet for a 

 period of 24 hours is sufficient. 



To keep down infestation in tobacco factories, many firms fumi- 

 gate all incoming tobacco in atmospheric vaults or vacuum chambers. 



For use in atmospheric vaults hydrocyanic acid at a dosage of 10 

 ounces of liquid hydrocyanic acid or its equivalent, ethylene oxide 

 at the rate of 2 pounds, ethylene oxide-carbon dioxide mixture at 20 

 pounds, or carbon clisulphide at 10 pounds per 1,000 cubic feet of 

 space should be used for a period of from 48 to 72 hours. Carbon 



