Contratoxification of Plant Growth-Regulators in Soils and on Plants

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Abstract
The persistence of toxicity of 2,4-D, butyl ester of 2,4-D (BE 2,4-D), Cu 2,4-dichlorophenoxyacetate [Cu(2,4-D)2], 2,4,5-trichloro-phenoxyacetic acid (2,4,5-T), and o-isopropyl n-phenylcar-bamate (IPPC) in a stored greenhouse soil was tested. Much toxicity of IPPC had disappeared after 12 days, but soil originally containing 220 ppm. of 2,4,5-T was toxic after 15 months. Soils containing Cu(2,4-D)2, 2,4-D, or BE 2,4-D at 220 ppm. had lost their toxicity after 15 months. These five compounds, except IPPC, were tested in a muck field soil. 2,4,5-T was the least toxic and persistent, and BE 2,4-D the most so. BE 2,4-D gave best control of weeds. Spading (plowing) decreased toxicity. Addition of Zeo-Karb H or Norbit A to soil containing 2,4-D decreased or eliminated toxicity. Norit A or Zeo-Karb H was dusted or sprayed in aqueous suspension on plants, and then plants were sprayed with aqueous 0.1% solns. of ammonium 2,4-dichlorophenoxyacetate, sodium 2,4-dichlorophenoxyacetate, triethanolamine salt of 2,4-D, isopropyl ester of 2,4-D, or BE 2,4-D, or dusted with a dust containing BE 2,4-D. Toxic effects of growth-regulators were decreased or eliminated by contratoxicants. Unless contratoxicants were applied within 15 min. after treatment with BE 2,4-D, very little protection was afforded.