Methyl Bromide Fumigation of Walnuts to Control Two Lepidopterous Pests, and Determination of Bromine Residue in Walnut Meats1

Abstract

Satisfactory control of larvae of the navel orangeworm, Myelots venipars in whole walnuts can be obtained by fumigating at atmospheric pressure with a dosage of 2 lbs. methyl bromide per 1000 cu. ft. for 2 hrs. when the nuts are in loosely woven cloth sacks,but not when the nuts are in sealed double-walled cellophane bags. Fumigation for larvae of the Mediterranean flour moth, Ephestia kuhniella in sealed double-walled cellophane bags did not give satisfactory control at atmospheric pressure with dosages of methyl bromide at 2 to 12 lbs. per 1000 cu. ft. and exposures of 1 to 3 hrs. Satisfactory control was obtained at a dosage of 2 lbs. methyl bromide per 1000 cu. ft, and 1 hr. exposure, with either sustained or released vacuum. When whole walnuts were vacuum-fumigated in sealed double-walled cellophane bags with 2 lbs. methyl bromide per 1000 cu. ft, the methyl bromide persisted over a period of 1 hr. to 21 days within the bag. The bromine residue of shelled walnuts fumigated under vacuum with 2.86 lbs. methyl bromide per 1000 cu. ft, although high at first, became almost constant after the first 24 hrs. Residues remained at the same level as much as 9 wks. after fumigation.