34 CIRCULAR 4 2 2, IT. S. DEPARTMENT OF AGRICULTURE 



cent. Since a hogshead of high-grade cigarette-type tobacco is valued 

 at about $300 (November 1936), this low cost presents no obstacle to 

 owners of infested warehouses who would fumigate periodically for 

 the control of the tobacco moth. 



RECOMMENDATIONS FOR TOBACCO MOTH CONTROL IN CLOSED WAREHOUSES 



Since it was demonstrated in the warehouse experiments sum- 

 marized in figure 22 that effective penetration of hydrocyanic acid 

 gas was rarely obtained deeper than 3 inches in hogsheads of tobacco, 

 it is recommended that periodic fumigations be carried out in ware- 

 houses during the warm months of the year. In most instances grown 

 larvae of the moth migrate to the surface of hogsheads of tobacco 

 and seek a sheltered place in which to pupate and transform to the 

 adult. From this time until the death of the moth, a period of 

 approximately 3 weeks, the insects remain at or near the surface of the 

 tobacco. The eggs, larvae, pupae, and adults that are near the sur- 

 face of the tobacco are all vulnerable to the gas, and effective con- 

 trol may be obtained by atmospheric fumigation at the opportune 

 time. Unsatisfactory results often occur when fumigation is per- 

 formed during the period when most of the brood is in the larval 

 stage, and feeding several inches below the surface. It is very im- 

 portant, therefore, to time the periodic fumigations to correspond 

 with the emergence of the broods of adults from May to October. 



The indicator shown in figure 21 may be used successfully to de- 

 termine the dates for fumigation. One of these indicators should 

 be placed in the warehouse for each 50,000 cubic feet of storage space. 

 They should be suspended at an angle of 45° approximately 6 inches 

 beneath electric lights. The most efficient light for use in connection 

 with the indicators was the 40-watt bulb. It is recommended for the 

 best results that only those lights over the indicators be allowed to 

 burn during the night. The following control program is suggested 

 for closed storage warehouses : 



(1) Place indicators in tobacco warehouses prior to the emergence of the 

 spring brood of tobacco moths. (In Virginia and North Carolina this date is 

 approximately May 15.) 



(2) When the average catch of tobacco moths is 30 per indicator per week, 

 fumigate the infested warehouses with hydrocyanic acid, using a dosage of 10 

 ounces of the liquid per 1,000 cubic feet, with an exposure of 72 hours. 



SAFEGUARDS IN FUMIGATION 



It would be impossible to overemphasize the importance of prop- 

 erly planning and carrying out the fumigation of tobacco warehouses 

 (i, p. SO) . The use of toxic gases, especialy hydrocyanic acid gas, is 

 dangerous to human life unless fumigators are equipped with prop- 

 erly fitted gas masks and are skilled in the use of the fumigant. Data 

 regarding suitable gas masks and other equipment required in fumi- 

 gation can be obtained from the fumigant manufacturers. The local 

 fire departments should be notified of the date of fumigation, and all 

 other agencies concerned should cooperate fully in carrying out regu- 

 lations designed to safeguard lives and property. 



After a warehouse has been prepared for receiving the gas, a care- 

 ful search should be made to determine that laborers or other persons 

 have vacated. Conspicuous signs should be placed on the doors and 



