Effects of Methyl Bromide Fumigation on the Viability of Barley, Corn, Grain Sorghum, Oats, and Wheat Seeds1

Abstract

Methyl bromide is a highly efficient fumigant, and is widely used for the fumigation of stored grain, mills, and warehouses. One of its undesirable qualities, at least for seed fumigation, is its phytotoxicity. Viability of seeds may be seriously impaired by excessive treatments with methyl bromide. Tests were conducted to determine the effects of methyl bromide on the viability of barley, corn, grain sorghum, oats, and wheat seeds when fumigated at 80°F. with different combinations of dosage, exposure, and seed moisture content. Gas analyses were made at the end of each fumigation to verify the methyl bromide concentrations. Germination tests were conducted 24 hours, 30 days, and with wheat only, 6 months after fumigation to observe immediate and delayed effects. There was a pronounced decrease in viability in some cases with the increased period of storage after fumigation. In some experiments standardized seedling evaluations were made so that sublethal, injurious effects could be observed. Many of the fumigated seeds sprouted but did not develop normally. A margin of tolerance usually exists between the dosages required for insect control and those which are lethal to high quality, dry seeds. This margin of tolerance is dependent upon the complex interaction of several variable factors, including (1) the fumigant dosage applied, (2) the seed moisture content, (3) the length of exposure, (4) the kind of seed, (5) the period and conditions of storage after fumigation, (6) the fumigation temperature, (7) the history of the seed (age, previous fumigations, etc.), (8) the ratio of commodity to total space in the fumatorium (the sorption capacity), and (9) leakage factors in the fumatorium. Some of these factors were explored here, some have been reported by other workers. In general, the results of the study show that little or no injury occurred when the following combination of condition, existed: (1) the seed moisture was less than 12%, (2) the dosage was less than 2 lb/1000 cu. ft., (3) the exposure period was less than 24 hours, and (4) the temperature was 80° F. High temperature, moisture, dosage, and long exposure all contribute to seed injury from fumigation. When combinations of fumigation conditions occur in which one (or more) of these variables is of a higher order than named above, moderate to extensive germination damage may be expected. The over-all relative order of tolerance of the five species tested was oats> barley> grain sorghum> corn> wheat.