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.

In greenhouse experiments, soil-incorporated combinations of 0,0-diethyl S-[2-(ethylthio)-methyl]-phosphorodithioate (phorate) or 0,0-diethyl S-[2-(ethylthio)-ethyl]-phosphorodithioate (disulfoton) with a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) resulted in increased cotton (Gossypium hirsutum L.) seedling growth as compared to trifluralin used alone. This result apparently was due to the greater numbers of secondary roots in the zone of incorporation. Phorate was more effective than disulfoton in overcoming the inhibitory effect of trifluralin on secondary root development. A comparison of granular and emulsifiable phorate showed no advantage for either formulation. The combination of phorate and trifluralin in a 1-inch soil core, into which seeds of cotton were planted and surrounded by trifluralin-treated soil, also increased secondary root development as compared to using trifluralin alone.

Single topical applications of monosodium methanearsonate (MSMA) affected cotton (Gossypium hirsutumL.) growth more than did similar disodium methanearsonate (DSMA) applications. There was usually no difference in yield among rates and dates with single applications of DSMA. Single applications of MSMA at later dates and higher rates reduced yields. Repeated topical applications of MSMA reduced yields and affected boll weight, lint percentage, number of seed per boll, and fiber fineness as compared with these properties of cotton treated once with MSMA. Response of cotton to MSMA was related to the number of applications and rate of herbicide. Repeated applications of DSMA affected cotton yield, lint percentage, and number of seed per boll less than did MSMA.

Single and repeat applications of herbicides or herbicide combinations were made over-the-top of young cotton (Gossypium hirsutumL.). DMSA (disodium methanearsonate) and MSMA (monodosium methanearsonate) applied 4 or 8 weeks after emergence had less effect on cotton yield, boll components, and fiber properties than did applications made 12 weeks after emergence. Most single, over-the-top applications of DSMA, fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea], or DSMA with fluometuron 4 weeks after emergence did not affect cotton yield, boll components, or fiber properties. One or two applications of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] or prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] alone, or with DSMA, reduced cotton yields. Applications of 1.1 and 2.2 kg/ha of fluometuron over-the-top of cotton 2 to 8 weeks after emergence did not affect cotton yields, boll components, or fiber properties.

Two incorporation methods were used in applying eight dinitroaniline herbicides before planting cotton (Gossypium hirsutumL.) for 3 yr. Penoxalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] gave the best stands of cotton. Nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] and dinitramine (N4,N4-diethyl-a,a,a-trifluoro-3,5-dinitrotoluene-2,4-diamine) resulted in the poorest stands. In 2 of 3 yr, cotton stands were better where herbicides were incorporated by listing only rather than by disking before listing. The eight herbicides were equally effective in annual grass control when followed by postemergence applications of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea]. An-56477 [N,N-bis(2-chloroethyl)-4-methyl-2,6-dinitrobenzenamine] was least effective in controlling annual broadleaf weeds. In 1972, cotton yield was reduced when An-56477 was incorporated by disking. In the average cotton yields for six tests, An-56477 produced significantly lower yields than any other herbicide except butralin [4-(1,1-dimethylethyl-N-(1-methylpropyl)-2,6-dinitrobenzenamine]. No differences in cotton fiber properties or boll components were due to herbicides or method of application.