Weed Control in Soils with 2,4-Dichlorophenoxyacetic Acid and Related Compounds and Their Residual Effects under Varying Environmental Conditions

Abstract

1. In Coloma sand an application of 2 p.p.m. of the sodium salt of 2,4-dichlorophenoxyacetic acid (sodium 2,4-D) killed from 95% to 98% of all weed seed present in the soil, while 8 or 16 p.p.m. made the soil virtually weed-free. Seeds of weedy grasses were killed in sand with concentrations of 8 and 16 p.p.m. of sodium 2,4-D. 2. There were no appreciable differences in weed-seed kill by the acid, the sodium salt, or the methyl ester of 2,4-D applied to Coloma sand. 3. Higher temperatures resulted in disappearance of toxicity of sodium 2,4-D from the soil more rapidly than did freezing or subfreezing temperatures, while the compound was equally effective as a weed-seed killer under all these temperatures. 4. Differences in pH value of Coloma sand did not appreciably affect the rate of loss of toxicity under the conditions of the experiment. 5. In water-saturated flats, sodium 2,4-D apparently disappeared in 3 weeks, while in air-dry flats toxicity was still present after 8 weeks. 6. Eight p.p.m. of sodium 2,4-D were ineffective in killing weed seeds in muck. 7. Corn was more highly resistant to 2,4-D materials under all conditions than either pea or radish.