A study was conducted from 1980 through 1984 to determine the residue expected on flue-cured tobacco when harvest was delayed at least seven days after application of MH at the maximum labeled rate of 2.5 kg/ha. Residues varied among locations and years but averaged 55, 59, 87, 105, and 57 ppm for 1980 through 1984, respectively over all plots and locations. The MH residue exceeded 80 ppm on a whole leaf basis in 36% of the samples; or conversely, in 64% of the samples the residue was below 80 ppm when values for all years, locations, and harvests were included. Predictions based on the data from this study show that, if MH is applied once during the season at the maximum recommended rate at least seven days before the first or second harvest, 44% of the flue-cured tobacco produced in North Carolina would contain residues exceeding 60 ppm; after stemming, the concentration in the lamina of the same tobacco would become about 78 ppm and would approximate the proposed tolerance of 80 ppm for tobacco products in the Federal Republic of Germany. A low but significant negative correlation between the average MH residue and yield of cured leaf was found for some locations in some years, but yield did not appear useful as a predictor for MH residues.

(Full article published with kind permission from "Tobacco International")