Mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl]-amino] phenyl] acetamide} was applied postemergence in soybean [Glycine max (L.) Merr.] fields and its effectiveness in controlling johnsongrass [Sorghum halepense (L.) Pers.], hemp sesbania [Sesbania exaltata (Raf.) Cory], and common cocklebur (Xanthium pensylvanicum Wallr.) was evaluated. In plots treated preplanting with trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), mefluidide gave 95% johnsongrass control when it was applied postemergence (over-the-top without surfactant) once at 0.90 kg/ha or twice at 0.44 kg/ha. Directed sprays of mefluidide at 0.22 to 0.67 kg/ha without surfactant were more effective on johnsongrass than similar treatments applied over-the-top. When 0.5% (v/v) nonoxynol [α-(p-nonyl-phenyl)-ω-hydroxypoly (oxyethylene)] surfactant was added, mefluidide at 0.44 or 0.67 kg/ha applied as directed or over-the-top sprays provided 76 to 90% johnsongrass control. Mefluidide at 1.12 kg/ha plus nonoxynol surfactant, applied as a directed spray, was required to provide 81% control of hemp sesbania. Directed sprays containing mixtures of mefluidide at 0.28 kg/ha plus dinoseb (2-sec-butyl-4,6-dinitrophenol) at 2.2 kg/ha, or mefluidide at 0.28 kg/ha plus a 2:1 mixture of naptalam (N-1-naphthylphthalamic acid)/dinoseb at 4.7 L/ha, effectively controlled 40- to 60-cm-tall hemp sesbania. A single, directed spray of mefluidide at 0.56 kg/ha plus nonoxynol provided 92% common cocklebur control, and mixtures of mefluidide at 0.28 kg/ha plus dinoseb at 2.2 kg/ha or naptalam/dinoseb (a 2:1 mixture) at 4.7 L/ha increased control above that provided by either of the herbicides alone.

The concentration of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} residue in Miller clay and Lufkin fine sandy loam was determined at various intervals following incorporated and nonincorporated applications in the field. Low levels of fluridone were present in Miller clay after 250 days while up to 25% remained in Lufkin fine sandy loam 385 days after treatment. Incorporation of fluridone increased its persistence in, Lufkin fine sandy loam but not in Miller clay. Fluridone degradation in Miller clay and Lufkin fine sandy loam was more rapid in the field than under controlled conditions. Fluridone degradation in sterilized Brennan fine sandy loam and Hidalgo sandy clay loam was significantly slower than in nonsterilized soil kept under the same conditions. These differences were not observed in Lufkin fine sandy loam and Miller clay.

Differential napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] tolerance by redroot pigweed (Amaranthus retroflexus L.) and prostrate pigweed (Amaranthus blitoides S. Wats.) was noted in field study. Redroot pigweed was readily controlled whereas prostrate pigweed was not. Germination studies in which both pigweed species were directly exposed to napropamide (0 to 25 ppm) indicated that prostrate pigweed was the most susceptible of the two species. Root growth rates of untreated prostrate pigweed were 30% greater than redroot pigweed. When seeds of both species were germinated in a 4-cm layer of napropamide in greenhouse study each species was controlled equally well. Exposure of germinating seedlings of the two pigweed species to napropamide 1 day before emergence resulted in differential control. Seedlings of redroot pigweed never developed beyond the cotyledon stage; whereas, prostrate pigweed seedlings were initially suppressed by the herbicide, but surviving plants continued to grow. An early preemergence application or mechanical incorporation of napropamide should enhance control of prostrate pigweed.

Weed competition in the commercial production of woody ornamentals results in substantial economic losses annually due to increased labor costs and reductions in plant growth and quality. Container and field experiments were established in 1975 and continued through 1976 to evaluate oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] as a weed control agent and to determine its effect on ornamentals at selected test sites throughout the United States. Test programs were conducted with container and field grown ornamentals at 10 locations during 1975 and subsequently increased to 12 locations in 1976. Rates evaluated included 3.4, 4.5, 5.6 and 11.2 kg/ha. Highly effective control of 17 weeds was obtained for 3-month periods at rates as low as 4.5 kg/ha. Oxadiazon gave commercially acceptable control of common groundsel (Senecio vulgaris L.), a very serious weed problem in containers. Control of common chickweed [Stellaria media (L.) Cyrillo], however, was poor at all rates tested. Ornamental tolerance to oxadiazon was generally excellent. Of the 50 ornamental species evaluated in 1975, only two displayed phytotoxic symptoms; scarlet firethorn (Pyracantha coccinea Roem.) and Chinese privet (Ligustrum sinense Lour.) at 5.6 and 11.2 kg/ha following three successive applications at 3-month intervals. In 1976 trials on 63 species, phytotoxic symptoms could not be reproduced on the above species; chemical intolerance was limited to growth inhibition of aloe yucca (Yucca aloifolia L.) at 5.6 and 11.2 kg/ha.

The triethylamine salt of triclopyr [(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid and the potassium salt of picloram (4-amino-3,5,6-trichloropicolinic acid) were applied as soil, foliar, and soil-plus-foliar treatments to greenhouse-grown huisache [Acacia farnesiana (L.) Willd.]. At 1.12 kg/ha, picloram was more effective (97 to 100% defoliation) than triclopyr (51 to 83%) in defoliating huisache. Triclopyr was more effective at 2.24 kg/ha than at 1.12 kg/ha in defoliating huisache, except when applied to the soil. Soil or soil-plus-foliar treatments of triclopyr at 2.24 kg/ha were not significantly different from those of picloram at 1.12 kg/ha 15 weeks after treatment. Triclopyr and picloram content was determined in and on leaves, stems, and roots at 0, 3, 10, and 30 days after treatment. More picloram than triclopyr was found in the leaves 30 days after treatment with foliar sprays at equal rates. Soil, foliar, and soil-plus-foliar treatments resulted in greater accumulation of picloram than triclopyr in stem tissue. Herbicide concentrations in roots were usually low. Reasons for the greater herbicidal activity of picloram than of triclopyr in huisache are not clear; however, the greater accumulation of picloram than of triclopyr in leaf and stem tissue may partially explain the difference in herbicide activity.

Studies were conducted on the effects of fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] on autotrophic growth (no sugar), heterotrophic growth (with sugar), and oxygen evolution and uptake and on the effects of MSMA (monosodium methanearsonate) on autotrophic growth and oxygen evolution and uptake by the unicellular green alga Chlorella pyrenoidosa Emerson strain (University of Texas). Two methods of analysis (probit and kinetic) were used to characterize the dosage-response of Chlorella to these herbicides. All measurements of Chlorella response to fluometuron were satisfactorily characterized by probit analysis, but only autotrophic cell number was adequately characterized by kinetic analysis. The fluometuron concentrations giving 50% inhibition on the probit plot were as follows: autotrophic cell number, 2.4 × 10−6M; chlorophyll at 400 nm, 3.3 × 10−6M; heterotrophic cell number, 2.4 × 10−6M; oxygen evolution, 20 × 10−6 M. The response of the alga to MSMA was stimulatory instead of inhibitory. Since this stimulation did not consistently range between 10 and 90% of the control, it was not possible to characterize the MSMA dosage-Chlorella response using either type of analysis.

In growth chamber studies, we measured the movement of cotyledons and leaves or leaflets in seedlings of nine weed species to determine: the magnitude of movement, whether movements followed a rhythmic pattern, and if rhythmic movements were endogenously controlled. Seedlings were always entrained under a 15-h light:9-h dark regime. Measurements were made at 3-h intervals for 3 to 4 days under four light regimes: alternating 15-h light:9-h dark; continuous light; one 15-h light:9-h dark span, followed by continuous light; and a 15-h light:9-h dark regime, in which the dark span was advanced 9 h (phase shift) when measurements were begun. No clearly defined pattern of leaf movement was found in wild mustard [Brassica kaber (DC.) L. C. Wheeler var. pinnatifida (Stokes) L. C. Wheeler]. Daily rhythmic leaf movements that did not appear to be endogenously controlled were found in redroot pigweed (Amaranthus retroflexus L.) and black nightshade (Solanum nigrum L.). Circadian rhythmic leaf movements that appeared to be under endogenous control were found in jimson-weed (Datura stramonium L.), common lambsquarters (Chenopodium album L.), common cocklebur (Xanthium pensylvanicum Wallr.), prickly sida (Sida spinosa L.), sicklepod (Cassia obtusifolia L.), and coffee senna (Cassia occidentalis L.).

The effects of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile}, and procyazine {2-[[4-chloro-6-(cyclopropylamino)-1,3,5-triazine-2-yl] amino]-2-methylpropanenitrile} on the photochemical reactions of isolated pea (Pisum sativum L. ‘Progress #9 Dwarf’) chloroplasts were studied. Atrazine, cyanazine, and procyazine inhibited electron transport but did not uncouple photophosphorylation. The primary site of inhibition for all three herbicides was on the reducing side of photosystem II; the electron transfer step between the primary electron acceptor (Q) and the plastoquinone pool of the electron transport chain is suggested as the site of action of all three herbicides. The amount of inhibition of electron transport observed after addition of herbicide to isolated chloroplasts was time-dependent for cyanazine and procyazine but not for atrazine. This was apparently due to a slower partitioning of cyanazine and procyazine from the aqueous phase of the reaction solution into the highly hydrophobic environment within the chloroplast membrane. Treatment of the thylakoid membranes with detergent reduced the time-dependent inhibitory nature of cyanazine and procyazine, and the ability of atrazine to block electron transport. A photosystem II-dependent electron transport assay and a chlorophyll fluorescence induction assay were used to determine the inhibitory potentials of atrazine, cyanazine, and procyazine. After allowing for differences in the rate of membrane penetration, I50 values of approximately 2 × 10−7 M were determined for each of the three herbicides.

Soybean [Glycine max (L.) Merr. ‘Hark’] plants responded similarly to a sublethal application of metribuzin [2-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] or to low light intensities. Both treatments increased soluble amino acid, ATP, nitrate reductase, and nitrate levels (up to 67, 140, 190, and 10,000%, respectively) and decreased soluble reducing sugars (33%), malate levels (86%), and the chlorophyll a/b ratio (24%). The similar response of light-limited and of chemically photosynthesis-inhibited plants is thought to be induced by a carbohydrate stress or another parameter related to a decreased rate of photosynthetic electron flow. However, during the induction process in shaded plants, light quality might play an important role in some cases. The results obtained with metribuzin and soybean plants are compared to and discussed together with (a) the results obtained by other authors working with s-triazine herbicides and (b) results obtained with methabenzthiazuron [N-(benzothiazol-2-yl)-N,N′-dimethylurea] in earlier experiments.

The effect of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] on the germination and growth of 14 plant species was investigated. A 10-3 M concentration of the herbicide did not reduce germination as much as 10% for corn (Zea mays L. ‘Pioneer 3369A’), English pea (Pisum sativum L. ‘Thomas Laxton’), sicklepod (Cassia obtusifolia L.), or wheat (Triticum aestivum L. ‘Coker 68–15′) but reduced germination of oat (Avena sativa L. ‘Coker 227′) to 0, lettuce (Lactuca sativa L. ‘Grand Rapids’) to 11%, and peanut (Arachis hypogaea L. ‘Florunner’) to 14%. A 10-6 M concentration did not affect the germination of any species tested. A 10-5 M concentration did not significantly decrease length or fresh weight of corn, morningglory, or wheat roots but had at least some adverse effect on all other species tested. At this concentration root length was less than 2/3 of the control for English pea, cucumber (Cucumis sativus L. ‘Ashley’), radish (Raphanus sativus L. ‘Scarlet Globe’), sicklepod, and soybean [Glycine max (L.) Merr. ‘Ransom’]. Metolachlor was supplied to germinating seeds of barley (Hordeum vulgare L. ‘Barsoy’), English pea, and corn either only in the shoot, seed, or root zone, or to all parts. One kg/ha applied in the shoot zone of barley and corn significantly reduced seedling height and dry weight but had no effect when applied in either the seed or root zone. Application in all zones was approximately twice as detrimental as when applied in only the shoot zone. Application of 4 kg/ha in only the shoot, seed, or root zones of English pea did not decrease seedling height or dry weight but application in all zones decreased these values about 98%. A 10-5 M concentration of metolachlor decreased leucine uptake by cucumber root tips but not its incorporation into protein. A 10-4 M concentration strongly reduced leucine uptake and slightly decreased leucine incorporation into protein.

Responses of six morningglories (Ipomoea spp.) and two Cassia spp. to 13 preemergence applied herbicides were determined at two locations in southern Alabama. Pitted (I. lacunosa L.), cypressvine (I. quamoclit L.), and willowleaf morningglories (I. wrightii Gray) were readily controlled with metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one]; entireleaf [I. hederacea (L.) Jacq. var. integriuscula Gray], tall [I. purpurea (L.) Roth.], and ivyleaf morningglories [I. hederacea (L.) Jacq.] were not controlled. Norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone] controlled cypressvine morningglory, but did not adequately control the other morningglory species. Perfluidone {1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl] methanesulfonamide} gave acceptable control of cypressvine and willowleaf morningglories, but gave poor control of other morningglory species. Sicklepod (C. obtusifolia L.) was controlled better than coffee senna (C. occidentalis L.) with 2.2 kg/ha diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and 2.2 kg/ha cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl]amino]-2-methylpropionitrile} controlled sicklepod better than coffee senna at one location each. Oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] was more effective in controlling coffee senna than sicklepod. Induction of population shifts toward incidental species of these genera seems unlikely based on the herbicides included in these experiments. In most cases the incidental species were more readily controlled than the prominent weed species.

Scanning electron microscopy (SEM) showed that EPTC (S-ethyl dipropylthiocarbamate) caused an aggregation of the epicuticular wax layer of corn (Zea mays L.). R-25788 (2,2-dichloro-N,N-diallylacetamide) prevented this aggregation when applied in combination with EPTC. Neither EPTC, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], nor R-25788 changed the weight of chloroform extractable epicuticular wax on corn leaves. EPTC apparently does not block lipid synthesis in corn as it does in other plant species. Thus R-25788 does not protect corn from EPTC or metolachlor by overcoming such a block. EPTC did affect wax arrangement on the leaf surface and caused an increase in the cuticular transpiration of corn and predisposed corn to injury from subsequent postemergence applications of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion). R-25788 protected corn against these deleterious effect.

Effects of soil water and herbicide vapors on the phytotoxicity of eight dinitroaniline herbicides to oats (Avena sativa L. ‘Dal’) were studied. Oat primary root length was inhibited more by the herbicides than was shoot length or shoot fresh weight. All of the herbicides, except oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide), inhibited primary root length through vapor activity. Vapors of dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) were most inhibitory. Herbicide vapor inhibition increased with temperature. Soil water affected oryzalin activity more than it did that of the other herbicides. Oryzalin phytotoxicity to the oat primary root was reduced more at the low soil water than was that of the other herbicides. Its low vapor activity apparently reduced its effectiveness in dry soil. Difference in magnitude of herbicide phytotoxicity between two soil moisture levels generally was more pronounced at lower herbicide concentration.

Pea (Pisum sativum L. ‘Elf’) root rot suppression by dinitroaniline herbicides could not be explained by a direct effect on the host. Pre-incubation of pea roots with 0.1 ppmw of oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) or trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) in solution culture did not alter their resistance to root rot. Furthermore, 0.1 ppmw of oryzalin or trifluralin did not alter the exudation of electrolytes or α-amino compounds from pea roots. Most of the dinitroaniline herbicides significantly inhibited mycelial radial growth of pathogen, Aphanomyces euteiches Drechs., at 1.0 ppmw and inhibited asexual spore production at 0.1 to 1.0 ppmw. Dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], and oryzalin inhibited A. euteiches mycelial growth and asexual reproduction more effectively than the other dinitroaniline herbicides studied. The production of motile zoospores, the infecting propagule of the pathogen, was the most sensitive stage in the life cycle and was completely inhibited by 0.01 ppmw of all dinitroaniline herbicides tested. Since this concentration is below that estimated in the soil solution at registered rates of application, inhibition of motile zoospore production is sufficient to explain root rot suppression. Inhibition of pathogen motility resulted in a 2-week delay in the infection of pea roots. This delay allowed sufficient additional plant growth that the peas could better withstand the effects of subsequent disease development.

Several herbicides applied either in the fall or spring at rates used for musk thistle (Carduus nutans L.) control had no deleterious effects on two cool-season grasses, smooth brome (Bromus inermis Leyss.) and intermediate wheatgrass [Agropyron intermedium (Host) Beauv.]. Herbicides used were 2,4-D [(2,4-dichlorophenoxy)acetic acid], 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], dicamba (3,6-dichloro-o-anisic acid), picloram (4-amino-3,5,6-trichloropicolinic acid), triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, and Dowco 290 (3,6-dichloropicolinic acid). Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] was included for comparative purposes because it is known to affect the protein content of some forage grasses. Effects on the quality of the forages were measured by in vitro dry matter disappearance (IVDMD), protein and KNO3 determinations. Intermediate wheatgrass was less susceptible to damage from the highest rates of picloram and atrazine than smooth brome.

Bioassay and gas chromatographic procedures were evaluated for their effectiveness in detecting fluridone [1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone] in soil. Bioassay procedures were limited to a detection range of 0.05 to 0.45 ppmw if grain sorghum (Sorghum bicolor (L.) Monech) was used. Visual estimations of chlorophyll content in affected plants, used as an indicator of fluridone concentration, were as reliable as spectrophotometric determinations. Gas-liquid chromatographic (GLC) procedures were less variable than the bioassay and had no upper limit of detection. Recovery of fluridone from treated soil ranged from 60 to 100 percent, depending on soil type. Soil water content affected percent recovery. Fluridone did not leach more than 1 cm in clay or sandy loam soils when up to 10 cm of water was passed through a soil column containing the herbicide, as determined by GLC. Extensive downward movement, 12 to 16 cm, occurred in a coarse sand when 5 or 10 cm of water was passed through the column.

Field experiments were conducted in 1974 and 1975 to evaluate the effect of seven herbicides applied preemergence and two herbicides applied postemergence on weed growth around 7-yr-old pecan [Carya illinoensis (Wang.) K. Koch ‘Elliott’ and ‘Desirable’] and 3-yr-old peach [Prunus persica (L.) Batsch ‘June Gold’] and to observe herbicidal tolerance as noted from visually expressed phytotoxicity. After 12 weeks, the best control of bermudagrass [Cynodon dactylon (L.) Pers.], purple nutsedge (Cyperus rotundus L.), and wild blackberry (Rubus cuneifolius Pursh) was obtained with glyphosate [N-(phosphonomethyl)glycine], napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] + glyphosate, and napropamide + terbacil (3-tert-butyl-5-chloro-6-methyluracil) + paraquat (1,1′dimethyl-4,4′-bipyridinium ion). The most effective overall control of yellow nutsedge (Cyperus esculentus L.), camphorweed [Heterotheca subaxillaris (Lam.) Britt. & Rusby], dogfennel [Eupatorium capillifolium (Lam.) Small], large crabgrass [Digitaria sanguinalis (L.) Scop.], and Florida pusley (Richardia scabra L.) resulted from napropamide + terbacil + paraquat. Herbicides used caused no visible toxicity to the immature pecan or peach trees.

Phorate {O,O-diethyl S-[(ethylthio)methyl] phosphorodithioate}, disulfoton {O,O-diethyl S-[2-(ethylthio)ethyl] phosphorodithioate}, linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea], or metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] when used alone did not reduce soybean [Glycine max (L.) Merr. ‘Calland’] grain yield or plant population. However, combinations of metribuzin with either phorate or disulfoton interacted synergistically to reduce both soybean grain yield and plant population significantly even at recommended rates of both chemicals. Combinations of linuron with either phorate or disulfoton at recommended rates did not reduce soybean grain yield or plant population. Greenhouse studies further substantiated the synergistic interaction of phorate or disulfoton with metribuzin.

Time- and concentration-course studies were conducted to determine the metabolic sites of action of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} in isolated mesophyll cells of cotton (Gossypium hirsutum L. ‘Acala SJ-1′) and red kidney bean (Phaseolus vulgaris L.). Cotton is resistant and bean is susceptible to fluridone. The herbicide was not metabolized in cells of either species during the 2-h incubation period. At the highest concentration (10-4 M) and longest incubation time (2 h), fluridone inhibited photosynthesis, RNA synthesis, and protein synthesis 59, 56, and 32%, respectively in bean and 24, 21, and 14% in cotton. Lipid synthesis and dark respiration were only slightly affected. The lowest concentration and the shortest incubation period that inhibited photosynthesis, RNA synthesis, and protein synthesis in bean did not have any significant effect in cotton. The difference in responses may contribute to the selectivity of the herbicide. Although photosynthesis appeared to be the primary site of action, RNA synthesis was also markedly inhibited. These inhibitions and the somewhat lower inhibition of protein synthesis may ultimately contribute to the herbicidal action of fluridone in the intact plant.

Ethofumesate, [(+)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] applied preemergence provided selective control of annual bluegrass (Poa annua L.) in perennial ryegrass (Lolium perenne L.) overseeded on dormant bermudagrass [Cynodon dactylon (L.) Pers. X C. transvaalensis Burtt Davy ‘Tifdwarf’] golf greens. Control in excess of 95% was obtained with single applications at the 2.2 kg/ha rate in 2 of 3 yr, but multiple applications were required when ethofumesate was applied at 1.1 kg/ha or less. Ethofumesate caused temporary cessation of bermudagrass growth when applied in the fall. February applications slowed the spring transition to bermudagrass.