Field soil studies with 14C-isopropalin (2,6-dinitro-N,N-dipropylcumidine) have demonstrated its biodegradability. None of the recognizable transformation products in soil accumulated beyond 4% of the amount of applied herbicide. After 15 months, approximately 25% of the applied isopropalin remained in soil, and less than 10% was observed after 28 months. Only negligible amounts of radioactivity were detected in crops grown in soil treated with the herbicide. Isopropalin and its recognizable transformation products were not detected in any of the plant tissues examined. Fractionation techniques indicated that the radioactivity was randomly distributed throughout the plant tissue.

In five field experiments conducted during 1972 and 1973, yellow nutsedge (Cyperus esculentus L.) was either undisturbed or removed from planting beds by hoeing 0, 2, 4, 6, and 8 weeks after cotton (Gossypium hirsutum L. ‘Acala SJ-1’) emergence. Yellow nutsedge undisturbed in beds increased from 23 plants/m of row at cotton emergence to 100 plants/m at harvest. Nutsedge competing with cotton for more than 4 weeks reduced yield of seed cotton. Nutsedge that competed all season reduced yields 34%, as compared with 20% when it competed for 6 and 8 weeks. Nutsedge that competed with cotton for more than 4 weeks reduced height and number of cotton plants and delayed maturity. Although nutsedge competition reduced yields and delayed maturity, it generally did not alter fiber properties. When nutsedge was removed at cotton emergence and was followed by 14 weekly hoeings, the final tuber population was reduced to 24% of the beginning population. When nutsedge removal was delayed for 6 weeks and was followed by nine weekly hoeings, a fourfold increase in tubers resulted. A further tenfold increase resulted when nutsedge was not removed.

At intervals of 3 to 56 days, propanil (3′,4′-dichloropropionanilide) at 4.5 kg/ha was applied after treatments of carbofuran (2,3-dihydro-2,2- dimethyl-7-benzofuranylmethyl carbamate) at 0.7 kg/ha. Their interaction injured rice (Oryza sativa L., ‘Starbonnet’) vegetatively, but did not reduce grain yields, milling quality, or seed viability. Leaf chlorosis and necrosis developed within 7 days after propanil treatment and lasted for 2 to 4 weeks. As the time interval between carbofuran and propanil treatments increased, leaf injury decreased. Older rice recovered more quickly than younger rice. Interaction of carbofuran and propanil did not cause chlorosis or necrosis of rice leaves when the insecticide was applied 5 days after the herbicide. Propanil alone, applied once at 4.5 kg/ha, or applied sequentially at 4.5 kg/ha each time, caused only slight chlorosis of rice leaves.

Rates of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) applied preplanting were combined with rates of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] applied postemergence in cotton (Gossypium hirsutum L. ‘Deltapine 16’). In another experiment, two levels of these herbicides were applied in three populations of cotton. All herbicide combinations improved weed control, compared to that of cultivated checks. Applications of 0.28, 0.42, and 0.56 kg/ha of trifluralin combined with 0.56 kg/ha of diuron controlled annual weeds and produced the highest cotton yields. Herbicide treatments had more influence than crop spacing on weed control and crop yield. Weed competition on cultivated checks affected boll weight, seed per boll, and fiber fineness.

The interaction of 2,4-D [(2,4-dichlorophenoxy) acetic acid], substrate, and calcium on eurasian watermilfoil (Myriophyllum spicatum L.) was determined. The effectiveness of 2,4-D was twice as great on plants grown on a substrate containing soil as it was on plants grown on a sand substrate. The presence of calcium chloride in sand culture during the period of 2,4-D uptake caused comparable or greater increases than sand culture without calcium in the effectiveness of 2,4-D. Possible differences in effectiveness of field treatments were calculated to be 48% greater at the highest natural concentrations of calcium than at the lowest concentrations in water of the Tennessee Valley. Calcium concentration and substrate altered the effectiveness of 2,4-D on eurasian watermilfoil.

Cotyledons of 6-day old etiolated cucumber (Cucumis sativus L. ‘Alpha Green’) seedlings treated on the second day with EPTC (S-ethyl dipropylthiocarbamate) accumulated 35 to 45% more protochlorophyll and 30 to 40% more glycolipids than the controls. on illumination the treated cotyledons accumulated chlorophyll faster than the controls. Exposure of cucumber cotyledons to a variety of amide, carbamate, and other thiocarbamate herbicides did not produce a similar effect. EPTC, was found to cause an increase in chlorophyll accumulation.

Using a modified in vivo nitrate reductase assay, all photosynthetic inhibitors tested were shown to effectively block light-dependent nitrite reduction in green leaf tissue. Nitrate reduction continued so that nitrite accumulated. Nitrite, vacuum infiltrated into leaf tissue, disappeared linearly with time when incubated in the light. Nitrite, vacuum infiltrated with a photosynthetic inhibitor, did not disappear but accumulated to even higher levels. The degree of inhibition of nitrite reduction was a function of herbicide concentration and time of incubation.

Three years of field experiments showed that Canada thistle. [Cirsium arvense (L.) Scop.] could be controlled with deeply injected soil fumigants without covering the soil with a tarpaulin. The degree of control depended on the kind of fumigant, the rate of application, and the depth of injection. Weed control with fumigants usually improved as the rate of application and depth of injection increased. The most effective treatment was 1,3-dichloropropene at 560 kg/ha injected to a depth of 46 cm. Good to excellent control of Canada thistle was also obtained with 1,3-dichloropropene at 280 kg/ha injected either 23 or 46 cm and ethylene dibromide at 160 kg/ha and chloropicrin + ethylene dibromide at 20 + 55 kg/ha injected at 46 cm. Results with ethylene dibromide and chloropicrin + ethylene dibromide were more erratic than with 1,3-dichloropropene. Increasing the percentage of chloropicrin in the combination reduced the control of Canada thistle.

Experiments were conducted to develop controls for cogongrass [Imperata cylindrica (L.) Beauv.] on noncrop areas. Single and multiple applications of herbicides were evaluated in field tests. All soil sterilants evaluated provided acceptable control. Single applications of TCA (trichloroacetic acid) at 56 kg/ha and dalapon (2,2-dichloro propionic acid) at 8.3 kg/ha controlled cogongrass without prolonged soil sterility. Multiple applications of amitrole (3-amino-s-triazole), paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), glyphosate [N-(phosphonomethyl)glycine] and dalapon markedly reduced cogongrass stands 1 year after application.

We compared eight weed control systems in soybeans [Glycine max (L.) Merr.] using several combinations of the herbicides trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), alachlor [2-chloro-2′,6′-diethyl-N-methoxymethyl)acetanilide], dinoseb (2-sec-butyl-,4, 6-dinitrophenol), chloroxuron [3-[p-(p-chlorophenoxy)phenyl]-1,1- dimethylurea], and linuron [3-(3,4-dichlorophenyl)-1- methoxy-1-methylurea] with or without cultivation to cultivation only and cultivation plus handhoeing. Cultivation plus handhoeing controlled the most weeds. Eight weed control systems using herbicides or herbicides plus cultivation controlled more weeds in soybeans than the system using only three cultivations. There was no significant difference in soybean yield between the system using three cultivations and six other systems using herbicides or herbicides plus cultivation. Trifluralin or alachlor applied as a preemergence treatment followed by postemergence treatments of chloroxuron, dinoseb, and linuron controlled weeds nearly as well as cultivation plus handhoeing. When dinoseb was applied repeatedly to leaves early after emergence, it severely injured soybeans, reduced soybean yield, and did not control sicklepod (Cassia obtusifolia L.). Sicklepod was the dominant weed species remaining at harvest.

Selective control of downy brome (Bromus tectorum L.) in alfalfa (Medicago sativa L.) was studied in 1971 and 1972. Herbicidal efficacy and alfalfa tolerance, yield, and percent and total protein were observed. The weed population was composed of almost 100% downy brome in 1971 and 1972. Herbicide treatments were applied early and late winter when both alfalfa and downy brome were dormant. Five herbicides afforded virtually complete downy brome control in 1971: pronamide [3,5-dichloro-N-(1,1-dimethyl-2-propynyl) benzamide] at 0.84 and 1.40 kg/ha, simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] at 1.12 kg/ha, terbacil (3-tert-butyl-5-chloro-6-methyluracil) at 0.84 kg/ha, paraquat (1–1′-dimethyl-4,4′-bipyridinium ion) at 0.56 kg/ha and cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile} at 3.4 kg/ha. All herbicide treatments reduced downy brome yields in 1972. Significantly higher alfalfa yields were closely related with lower downy brome yields. In 1972, alfalfa treated with propham (isopropyl carbanilate), cyanazine, pronamide and terbacil also was higher in second cutting yields than the control. Twelve of the 23 treatments, including all triazine herbicides, increased first harvest alfalfa protein percentage in 1972 although differences were not observed in 1971. Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)-acetanilide] spring-applied in 1971 at 5.62 kg/ha was the only treatment causing visual alfalfa injury.

Concentrations of TCA (trichloroacetic acid) were determined in irrigation water after the sodium salt formulation had been applied to the banks of dry canals at 82 kg/ha for weed control. When the canals were refilled about 5 months after treatment, maximum concentrations of TCA detected in the water ranged from 53 to 297 ppb. The concentration was highest during the first hour of waterflow. The maximum concentration increased at a rate of 26 to 30 ppb/km of canal treated, unless surface runoff or reduced flow volumes caused abnormal flows in the canals. With one exception, no TCA was detected in the water after 4 hr of flow.

Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], and benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) were applied at two rates for five consecutive years (1966 through 1970) as soil-incorporated treatments to cotton (Gossypium hirsutum L. ‘Acala SJ-1’) before the preplanting irrigation. Repeated applications did not significantly affect stand or yield of cotton. Soil samples taken to depth of 120 cm showed that herbicide residues were confined to the tilled zone of soil (upper 30 cm), and about 80% of the residue was in the upper 15 cm of soil. The amount of herbicide residue found annually in the upper 15 cm of soil varied with herbicide and with season. Residues 15 months after final application had been reduced markedly, but were still sufficient to injure sensitive crops. Residues at 30 months had been reduced to innocuous amounts.

Laboratory, greenhouse, and field experiments were conducted in 1972 and 1973 on the efficacy of controlling yellow nutsedge (Cyperus esculentus L.) in soybeans [Glycine max (L.) Merr.] with bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2,2-dioxide], glyphosate [N-(phosphonomethyl)glycine], and perfluidone [1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl] methanesulfonamide]. Young nutsedge plants (four- to six-leaf stage) were more susceptible to foliar sprays of the three herbicides than were older (six- to eight-leaf stage) plants. Foliar application of bentazon resulted in slow acropetal translocation of the herbicide, but killed the parent tubers. Good coverage of the foliage by bentazon sprays is essential, because the bentazon frequently kills only the foliage contacted by the spray. Applied as a postemergence broadcast spray, glyphosate injured soybeans severely at rates higher than 0.3 kg/ha, but did not satisfactorily control yellow nutsedge at rates less than 2.2 kg/ha. Perfluidone was active on yellow nutsedge when applied to either soil or foliage; yellow nutsedge was controlled best with preplant incorporated treatments at 4.5 kg/ha. Applications of 4.5 kg/ha perfluidone in the field significantly injured soybeans and reduced yields.

MSMA (monosodium methanearsonate) and DSMA (disodium methanearsonate) killed 27 to 90% of the broomsedge (Andropogon virginicus L.) plants when applied at 1.1 to 6.7 kg/ha in July. These rates did not reduce yields of smooth bromegrass (Bromus inermis Leyss.) or affect the density of Kentucky bluegrass (Poa pratensis L.) growing in association with the broomsedge.

In greenhouse studies, soil applications of 14C-methyl-labeled glyphosate [N-(phosphonomethyl)glycine] were not readily absorbed by corn (Zea mays L. ‘Michigan 400’) and soybean [Glycine max (L.) Merr. ‘Hark’]. However, glyphosate available to plants in sand culture was absorbed. Wheat (Triticum aestivum L. ‘Avon’) a sensitive bioassay plant, was used to detect the herbicide. Clay loam and muck soil rapidly inactivated 56 kg/ha of glyphosate. Autoclaving of the soil did not prevent the inactivation of glyphosate. In a sandy clay loam soil, application of 56 kg/ha of glyphosate decreased plant growth with increasing pH. Additions of 98 or 196 kg/ha of phosphate to the soil surface decreased glyphosate inactivation in the soil. It is postulated that initial inactivation of glyphosate in soil is by reversible adsorption to clay and organic matter through the phosphonic acid moiety.

Glyphosate [N-(phosphonomethyl)glycine] was readily bound to kaolinite, illite, and bentonite clay and to charcoal and muck but not to ethyl cellulose. Fe+++ and Al+++-saturated clays and organic matter adsorbed more glyphosate than Na+ or Ca+-saturated clays and organic matter. Glyphosate appears to be bound to the soil through the phosphonic acid moiety as phosphate in the soil competed with 14C-glyphosate for adsorption sites. Glyphosate mobility in the soil was very limited and was affected by pH, phosphate level, and soil type. The 14C-glyphosate was biodegraded in soil to 14CO2 possibly by co-metabolism. Potentiometric titrations of the compound gave pKa values of 2, 2.6, 5.6, and 10.6.

Radioactive glyphosate [N-(phosphonomethyl)glycine] is rapidly absorbed with a large portion of the 14C translocated to the rhizomes and untreated shoots of quackgrass [Agropyron repens (L.) Beauv.]. The adjuvant used with glyphosate was important in determining its phytotoxicity to quackgrass. In other perennial weeds and annual species, glyphosate also moved to the areas of highest metabolic activity. In Canada thistle [Cirsium arvense (L.) Scop.], bentazon (3-isopropyl-1H-2,1,3-benzothiadiazin-(4) 3H-one 2,2-dioxide) at 2.24 kg/ha applied prior to treatment with 14C-glyphosate reduced 14C translocation. Iron or nitrilotriacetic acid (NTA) did not appear to effect glyphosate activity on wheat (Triticium aestivum L. ‘Avon’). The respiration of quackgrass treated with glyphosate was significantly reduced 9 days after treatment. Glyphosate reduced total photosynthesis more in quackgrass than in wheat.

The response of corn (Zea mays L.) and fall panicum (Panicum dichotomiflorum Michx.) to postemergence herbicide applications at three stages of growth was examined. Early postemergence application of cyanazine 2-[[4-chloro-6-(ethylamino)-s-triazine-2-yl] amino]-2- methylpropionitrile at 3.4 kg/ha provided the best control with minimum crop injury and greatest corn yield. A reduction of 25% in corn yield resulted when fall panicum was removed by hand at the seven to eight-leaf stage as compared to removal of plants with two leaves. Various adjuvants increased cyanazine action on both fall panicum and corn in field and greenhouse experiments; however, field trials showed no differences in grain yield at harvest. In the greenhouse, less corn injury was observed with a vegetable oil additive than with other adjuvants.