Effects of Organic Arsenical Herbicides on Cotton Response and Chemical Residues

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Abstract
The influence of timing and method of application of sodium or disodium salts of methanearsonic acid (MAA) on cotton (Gossypium hirsutum L.) response, arsenic content of seed, and arsenic content of soils, was studied in field experiments in California, Arizona, and Mississippi. Methods of application consisted of directed and topical sprays. Directed sprays were applied to cover the small weeds in the drill row with a minimum of contact on cotton leaves more than 2 to 3 inches above the ground. Topical sprays were applied from nozzles positioned over the cotton in such a way that the entire cotton plant was subject to coverage. Rates of application were either 2 or 3 lb/A of the salts, and either two or three applications were made to treated plots. Cotton appeared highly tolerant to directed applications. A topical application to cotton 2 to 4 inches slightly reduced yields, but topical applications made at later stages of growth caused progressively severe reductions in yields and delayed maturity. The arsenic content of cottonseed from treated plots was not significantly higher than in that from untreated checks providing that applications were restricted to prebloom stages. Either directed or topical applications made during the blooming stage resulted in detectable increases of arsenic in the cottonseed. The effect of the treatments on arsenic content of soils was relatively small in comparison with natural levels, but the effect was detectable at one of the three locations.