Longevity of Parathion, DDT and Dichlorodiphenyl Dichloroethane Residues on Field and Vegetable Crops1

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Abstract
The plants were grown in exptl. plots on commercial farms. The insecticides were applied as dusts and sprays for practical insect control. Plant samples were collected before and during harvest and extracted with benzene. The solvent was evaporated, and the residues were analyzed for the toxicants by colorimetric methods. Residues were analyzed on the following crops: alfalfa, corn plants, onions, pea vines, scallions, and turnips. Translocation analyses were made on shelled peas, corn stalks and kernels, potato tubers and turnips. Virtually no parathion residues were recovered on crops harvested 12 or more days after the last application of 0.5% to 1% dusts or sprays containing 0.125 to 0.25 lb. per acre. However, pea vines sprayed with 0.5 lb. parathion per acre showed 0.1 ppm. of the toxicant at harvest, 19 days after spraying. Corn dusted 5 times with 3% DDT and harvested 13 days after the last application contained 13.1 ppm. of DDT. Similarly, corn dusted 5 times with 5% TDE analyzed 20.3 ppm. of the toxicant. The rainfall during this period was only 0.99 inch. This indicates that in absence of sufficient rainfall, comparatively large quantities of DDT and TDE residues may be retained by corn plants at harvest. None of the 3 toxicants were found translocated in any appreciable quantities in plant tissues from dusts, sprays or soil treatments.