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 E-I192 September 1939 
 
 United States Department of Agriculture 
 Bureau of Entomology and, Plant CJuarantinia 
 
 FUMI&ATION OF ?ETCH SEED TO CONTROL THE VETCH BHUCKID 
 
 By Lon. A. Hawkins, Division of Control Investigations 
 
 In experimental work on fumigation of vetch seed for the vetch 
 bruchid, Bruchu s brachialis , carried on in 1936 and 1937 "by A. C« Johnson, 
 J. S. Pinckney, J. W, Bulger^ and A, M. Phillips, three methods of fumiga- 
 tion were developed which gave complete mortality of the insects in in- 
 fested seed. Certain of these methods have been used quite extensively 
 under commercial conditions with excellent results. The three methods 
 are— 
 
 (1) Euraigation with hydrocyanic acid at atmospheric pressures 
 with a dosage of U pounds of hydrocyanic acid per 1,000 cubic feet and an 
 exposure of 2U hours at a temperature of 70^ F, or above, and a load not 
 more than 15,000 pounds per 1,000 cubic feet, 
 
 (2) Vacuum fumigation, fumigation under a pressure reduced to the- 
 equivalent of 2 inches 01 mercury or a HS-'inch vacuum under normal atmos~ 
 pheric pressure at sea level, with a dosage of 7 o-onces of hyrocyanic acid 
 per 100 cubic feet of chamber space at a temperature not lower than 70^ F. 
 for a period of 2 hours, with a load not more than 15,000 pounds per 1,000 
 cubic feet, 
 
 (3) Carbon disulphide fumigation, fumigation at normal atmospheric 
 pressures with a dosage of 20 pounds of carbon disulphide per 1,000 cubic 
 feet of chamber space for a period of 2^ hours, at a temperature not lower 
 than 70® F., the load being not more than 12,000 poundr. per 1,000 cubic 
 feet. 
 
 Under all three methods of fumigation the sacks of vetch seed should 
 be separated so that the fumigant is in contact with as much of the surface 
 as possible. 
 
 These investigations have been continued, and it has been shown 
 that both methyl bromide and chloropicrin can be used for fumigation of 
 vetch seed with assurance of complete kill of any bruchids present. 
 
 The dosage of chloropicrin found to be effective was I-I/2 pounds 
 per 1,000 cubic feet of space, the chloropicrin being volatilized into 
 the chamber and mixed thoroughly with the air by raeans of a fan. The 
 fan should be operated throughout the Tajnigation period. Starring the 
 air was found to be essexitial, as in cases where the fumigant v/as not 
 stirred considerable survivr.l occufred. In four experiments at temp- 
 eratures ranging from 6l^ to 76*^ no survival occurred in an estimated 
 
UNIVERSITY OF FLORin/> 
 
 3 1262 09224 6825 
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 population of 6,292. In one test lA v.-hich the air was not agitated, 
 with an estimated population of 1,792, there wore nine survivals. In 
 one test in which l^O-pound sacks were used, with i>n estimated population 
 of 1,U72, there was one survival. Those experiments indicate that a 
 treatment at 70*^ ■?•. with a dosage of l-l/2 pounds of chloropicrin per 
 1,000 cubic feet and a load of 12,900 -pounds por 1,000 cubic feet, ap," 
 pro::imately the same as in carload shipments, in a tight chamber, such 
 as a refrigerator car, the aif-gas mixture being circulatad throughout 
 the period of 2k hours, would kill any vetch bruchids which night be 
 present in the seed in 100-pound sacks neparated so that the gas could 
 come in contact with all sides of the Ess.ck. 
 
 In nine tests with vetch fQC.d fu^.igated at a dosage of 1 to I-1/2 
 pounds of chloropicrin for a period of 2^ hours, the germination of the 
 treated seed was 31.1 percent and of the untreated seed 3J> .1 percent, 
 indicating that there was no appreciable injury to the seed from 
 fumigation. 
 
 With methyl bromide in six tests with a dosage of 3 pounds per 
 1,000 cubic feet and a period of exposure of U hours, at temperatures 
 ranging from 67° to 71°. there was complete mortality in all cases in 
 an estimated population of 3 fO'^^^- insects. There was one survival when 
 the dosage of 3 pounds for 2 hours was used with an estimated population 
 of 1,63^+. From these data it is indicated th;\t complete mortality of 
 the vetch bruchid in seed can bo obtained when the seed is fumigated 
 with methyl bromide at a dosage of 3 pounds per 1,000 cubic feet for a 
 period of k hours, at a temperature of 70^ '^' The load in these tests 
 was 12,900 pounds per 1,000 cubic feet or at the rate of 30,000 
 pounds to the carload. 
 
 Germination tests of 12 samples of treated and untreated seed from 
 the same lots gave average gjn.dnation of 8S.5 percent for the treated 
 seed and 89.7 percent for the uiitroated seed, indicating that there was 
 apparently no appreciable lowering of the viability of the seed by this 
 treatment. 
 
 It should be emphasized that the air-gas mixture must be stirred by 
 means of a fan during the fumigation period and that the fumigation chamber 
 must be tight. A refrigerator car with the drips plugged and the hatch 
 plugs firmly iis.-tjd makes an excellent fumigation chamber.