Evaluation of cured leaf residues of several common pesticides used in dark air-cured and dark fire-cured tobacco
Pesticide residue trials were conducted from 2011 to 2017 to evaluate cured leaf residues of eight commonly used pesticides registered for use on dark tobacco in the United States. Pesticides tested included azoxystrobin, acephate, lambda-cyhalothrin, and maleic hydrazide in 2011-2014, and spinosad, butralin, flumetralin, and sethoxydim in 2015-2017. Each pesticide was applied using a maximum allowable dose philosophy, where maximum rates and number of applications according to product labels were used. Timing of applications were similar to standard timings used by growers. However, final applications were made at the minimum preharvest interval allowed on the product labels. These field experiments were conducted as two adjacent experiments each year. Both trials were transplanted at the same time with the same dark tobacco variety. All applications were made at the same time for both trials, and both trials were stalk-harvested at the same time. The only difference was that one trial was air-cured while the other trial was fire-cured. Following curing, two samples of 0.2 kg of cured leaf were collected from each plot, one sample from the upper stalk area and the other from the lower stalk area. Average residues in air-cured tobacco ranged from 3.22 to 12.97 ppm for azoxystrobin, 1.58 to 4.1 ppm for acephate (methamidophos), 0.49 to 0.92 ppm for lambda-cyhalothrin, 53 to 83 ppm for maleic hydrazide, 0.51 to 5.40 ppm for spinosad, 1.29 to 2.12 ppm for butralin, and 1.32 to 11.77 ppm for flumetralin. Average residues in fire-cured tobacco ranged from 2.2 to 12.95 ppm for azoxystrobin, 0.69 to 1.0 ppm for acephate (methamidophos), 0.46 to 0.78 ppm for lambda-cyhalothrin, 48 to 70 ppm for maleic hydrazide, 1.17 to 6.27 ppm for spinosad, 1.35 to 2.13 ppm for butralin, and 0.89 to 7.73 ppm for flumetralin. No sethoxydim residues were found in any sample.