Decomposition of 11 dinitroaniline herbicides was determined following 7 days exposure to unfiltered solar radiation in July and compared with that in the dark. Radiolabeled herbicides were applied at 1 kg/ha to dry soil thin layer plates. Decomposition of all dinitroanilines was higher when exposed to sunlight than if held in the dark under otherwise similar conditions. Thermal decomposition was noted for all dinitroanilines except profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine] and dinitramine(N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine). Photodecomposition for each herbicide was: 7.8% AC 92390 [N-(1-ethylpropyl)-2,6-dinitro-3,4-dinitro-3,4-xylidine], 8.2% isopropalin (2,6-dinitro-N,N-dipropylcumidine), 9.0% butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine], 9.9% pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine], 17.1% benefin(N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), 18.4% trifluralin (α,α,α-trifluoro-2,6-dinitro-N-N-dipropyl-p-toluidine), 26.6% oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide), 30.4% fluchoralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], 40.6% nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], 47.6% profluralin, and 72.3% dinitramine.

Vapor losses of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-p-toluidine), and nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] were studied under controlled laboratory conditions using a Florisil vapor trap. No nitralin vapor losses were detected at 50 C from a Lakeland loamy sand at field capacity with an air flow rate of 0.04 m3/hr for 3 hr; whereas, 24.5% and 12.5% of trifluralin and benefin, respectively, were lost as vapors. Volatility of trifluralin and benefin increased with increasing temperatures of 30, 40, and 50 C and increasing soil moisture from air dryness to field capacity. Vapor losses from granular benefin were similar to the spray applications at 30 and 40 C. Volatilization of granular trifluralin was reduced when compared to the spray application at 40 C and 30 C but was similar for both formulations for benefin. No significant losses from photodecomposition were noted for trifluralin, benefin, or nitralin when comparing radiated and unradiated soil surface treated samples.

Glyphosate [(N-phosphonomethyl) glycine] was evaluated for three years as a foliar herbicide for the control of johnsongrass [Sorghum halepense (L.) Pers.]. In the greenhouse, maximum rhizome kill resulted from foliar applications of glyphosate at 1.12 to 2.24 kg/ha. In several field studies, plowing from 4 to 21 days following glyphosate application had little effect on johnsongrass control; plowing within 0.5 hr following glyphosate application resulted in less control than when plowing was delayed for 12 days. In stage of growth studies, control was better when glyphosate was applied to johnsongrass in the boot to full head stage than earlier when johnsongrass was 45 to 60 cm in height. In ‘York’ soybeans [Glycine max (L.) Merr.], glyphosate at 1.12 to 2.24 kg/ha applied 12 to 14 days prior to plowing and trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) incorporated prior to planting provided good johnsongrass control. In ‘3369A’ corn (Zea mays L.) directed postemergence applications of glyphosate provided good johnsongrass control but caused extensive crop injury.

Field and greenhouse studies were conducted to determine the influence of soil organic matter on herbicidal activity using four Pocomoke soils with organic matter contents of 4.8, 7.0, 11.9, and 17.0%. In field experiments, control of giant green foxtail [Setaria viridisvar.major(Gaud.) Posp.] was greater than 75% from all treatments of 2-chloro-2′,6′-diethyl-N-(methoxymethyl) acetanilide (alachlor), 2-chloro-N-isopropylacetanilide (propachlor), andN,N-diallyl-2-chloroacetamide (CDAA) with no statistical differences between chemicals, rates, or organic matter levels. Control was statistically lower from all 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) treatments except 2.6 kg/ha at 7% organic matter and 4.4 kg/ha at 7 and 17% organic matter. Under greenhouse conditions, giant foxtail (Setaria faberiHermm.) was used to establish GR50values on soils or soil mixtures containing 0.8, 1.9, 3.9, 6.4, 11.0, and 18.7% organic matter for the herbicides used in the field study and for 2-chloro-N-(1-methyl-2-propynyl)acetanilide (prynachlor). Generally as organic matter levels increased, the GR50values for herbicides increased; the rate of GR50increase varied with herbicides. A ranking of herbicides from most toxic to least toxic is: propachlor>alachlor>prynachlor>CDAA. Atrazine GR50values varied from a low similar to propachlor at 0.8% organic matter to 20 times greater than propachlor at 17% organic matter.

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