CONTROL OF INSECTS ATTACKING STORED TOBACCO 23 



all storage centers is of much importance to the entire tobacco in- 

 dustry. The adults disperse from infested warehouses in large 

 numbers and rein f est fumigated tobacco or often invade nearby 

 manufacturing plants. One heavily infested warehouse in a storage 

 center such as Richmond, Va., or Durham, N. C, might serve to 

 spread infestation throughout the locality. Unless prompt measures 

 are taken to control infestations, the population of the insects will 

 increase manyfold the following season. 



The closed type of tobacco warehouse (fig. 17) is constructed of 

 wood, brick, or reinforced concrete, and usually the roof is of tar 

 and gravel. In some instances the floors consist of a foundation of 

 crushed rock covered with soil and a layer of coal cinders. In many 

 closed warehouses, however, the floors are constructed of concrete or 

 closely fitted wooden boards. The buildings may be one or several 

 stories high with enough ventilators through the walls and roof 

 to provide the proper aeration for the fermenting tobaccos. Wooden 

 supports 6 by 6 inches are usually placed along the floor, upon which 

 the hogsheads and cases of leaf tobacco are stacked during the aging 

 period. The volume of these warehouses varies greatly, some contain- 

 ing not more than 25,000 cubic feet and others more than 400,000 cubic 

 feet per section. Many units of closed storage consist of 20 to 25 

 sections of warehouses separated by fire walls, with a total volume of 

 several million cubic feet. Tobacco warehouses of this size frequently 

 store more than 50 million pounds of tobacco at a time. Since it has 

 not proved feasible to move these large stocks of tobacco through special 

 fumigating apparatus, the most practical and economical method of 

 control thus far developed has been periodic fumigation with hydro- 

 cyanic acid gas. This gas is poisonous, and pages 39 and 40 should 

 be read before attempt is made to use it as a f umigant. 



PERIODIC FUMIGATION 



When catches from traps indicate that the insects have increased to 

 a point where control measures are advisable, the main dependence 

 should be placed on periodic fumigation of the warehouse. The ten- 

 dency is sometimes prevalent to postpone the application of direct con- 

 trol measures and place too much reliance on low winter temperatures 

 or other natural controls. If a satisfactory dosage of fumigant is 

 applied promptly upon the appearance of insects in the warehouse, the 

 population can be held to a low level or sometimes eliminated in build- 

 ings of tight construction. Results of the periodic application of 

 hydrocyanic acid gas for control of the tobacco moth are shown in 

 figure 18. 



SEALING OF WAREHOUSES 



To obtain effective results in the control of insects, warehouses must 

 be sealed properly prior to fumigation. This sealing makes possible 

 the retention of the maximum concentration of gas. Materials for this 

 purpose include several commercial grades of waterproof paper, tar 

 paper, durable cardboard for ventilators, and elastic roofing cement. 

 All openings in the walls and ceiling, such as ventilators, eaves, win- 

 dows, elevator shafts, skylights, and doors, should be made gas-tight 

 prior to the application of the fumigant. Paperhangers' paste, mixed 



