Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] applied as a preplant treatment at rates of 2.24 to 8.96 kg/ha was evaluated for the control of perennial grasses and the establishment of jeffrey (Pinus jeffreyi Grev. & Balf.) and ponderosa (Pinus ponderosa Laws.) pine transplants. The most consistent and effective rates of atrazine (6.72 and 8.96 kg/ha) reduced grass herbage biomass an average of 72% over a 3-yr period and increased average final survival of transplants from 1% on the control to 66% with treatment. These rates also gave continued grass control for at least 3 to 4 yr after treatment. Stem diameter and top growth tended to be greater on the most effective treatments. High survival and increased growth of transplants on these treatments were attributed to low soil moisture tensions and increased NO3-N accumulation throughout the summer to depths of 30 cm during the year of planting and subsequent years.

The adsorption of picloram (4-amino-3,5,6-trichloropicolinic acid) was determined on an Aiken silt loam, on three cation exchange resins and on a single anion exchange resin. Adsorption data were evaluated using parameters in the Freundlich equation and their dependance upon cationic composition of the exchange complex, the ionic composition of the equilibrium solution, and the equilibrium solution pH. For the Aiken soil saturated with metallic cations the order of decreasing picloram adsorptive capacity was Fe+3 = Cu+2 > Al+3 > Zn+2 > Ca+2 > native soil. Increases in adsorption compared to the native Aiken soil could be explained on the basis of decreases in the equilibrium solution pH except for Fe+3, Zn+2, and especially the Cu+2 treatments. The adsorptive capacity of the Aiken soil was altered by the addition of several salts simulating addition of fertilizer salts. The Cu+2 and Zn+2 salts were the only treatments showing increased adsorption which could not be explained readily by pH changes. KH2PO4 and NH2CONH2 (urea) reduced picloram adsorption. Dowex 50-1 × 4, a strongly acidic cation exchange resin, showed increased picloram adsorptive capacity in the order Cu+2 > Al+3 > Ca+2 > Zn+2 = H+. Cellex CM, a weakly acidic cellulose exchanger had increased adsorptive capacities in the order of Cu+2 > Ca+2 > Al+3 > Na+ > Fe+3 > Zn+2. Picloram adsorption by an anion exchange resin at pH 6.1 was nearly 100%. These results suggest that complex formation of picloram with polyvalent cations on the exchange complex is likely especially for Cu+2 and to a lesser extent Fe+3 and Zn+2. In soils such complex reactions would most probably involve organic matter, polyvalent cations, and picloram. The formation of chelate ring species is proposed.

Field studies were conducted in 1975 and 1976 at Urbana, Illinois, to evaluate soybeans [Glycine max (L.) Merr. ‘Amsoy 71′] as a potential rescue crop following the use of 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} with corn (Zea mays L.). Preplant incorporated and preemergence applications of each herbicide were made at the recommended broadcast rates to Dana and Flanagan silt loams. Corn was removed and soybeans were planted 7, 13, and 21 days (1975) or 10, 15, and 23 days (1976) following herbicide application. Visual injury ratings, stands, and yields for soybeans were determined. In spite of varying degrees of visible injury and stand reductions, yields were not reduced significantly when soybeans were planted 3 weeks after cyanazine or procyazine application.

Metribuzin-3-14C [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] was absorbed, translocated, and metabolized by both metribuzin-tolerant ‘Essex’ and metribuzin-sensitive ‘Coker 102’ soybean cultivars [Glycine max (L.) Merr.]. After 48 h Coker 102 accumulated 40% greater metribuzin equivalents in the shoots than Essex, but Essex shoots contained only 29% as much unaltered metribuzin as Coker 102, 1.08 and 3.68 μg per g dry weight, respectively. Essex is resistant to metribuzin primarily owing to a capacity to rapidly detoxify metribuzin to DA [6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], to at least seven unidentified metabolites which remained in the aqueous fraction, and to an insoluble fraction. The unidentified metabolites in the aqueous fraction constituted the major detoxified breakdown products in both cultivars.

Wheat (Triticum aestivum L. ‘Holley’) was grown for 14 days in 0.5 strength Hoagland and Arnon's complete mineral nutrient solution containing 0. 15.6, 31.25, 62.5, 125.0, or 250.0 ppbw EPTC (S-ethyl dipropylthiocarbamate). Gibberellic acid (GA) content, as measured by gas-liquid chromatography, was decreased 96.4% by 125.0 ppbw EPTC. When 0.05 μCi mevalonic acid-2-14C-(MVA-2-14C) (DBED salt) (0.15 mCi/mg MVA) was added to the nutrient solution, incorporation of MVA-2-14C into total kaurenoids was decreased 90% by 250 ppbw EPTC. Metabolism of kaurene was reduced by 250 ppbw EPTC with resultant 3-fold accumulations of kaurene.

When clay granules containing chlorpropham (isopropyl m-chlorocarbanilate) were applied to the surface of moist soil, the herbicide gradually moved to the atmosphere as a vapor and little entered the soil. Chlorpropham killed seedlings of field dodder (Cuascuta campestris Yunck.) and largeseed dodder (C. indecora Choisy) effectively whether it contacted them in the soil or in the air above the soil.

Twenty-eight commercial soybean [Glycine max (L.) Merr.] cultivars of maturity classes V through VIII were evaluated for differences in response to metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] 0.125 ppm w/w in hydroponic culture. Top dry weight (TDW) of treated ‘FFR 666’ soybeans equaled that of the cultivar check and five other cultivars were not significantly different (P = 5%). ‘Semmes' was most sensitive to the herbicide with TDW 40% of cultivar check. ‘Tracy’ and ‘Coker 156’ were not significantly different (P = 5%) from Semmes. The other cultivars tested were intermediate in response to metribuzin.

Seven herbicides were applied to the soil surface or subsurface for control of honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell] and Macartney rose (Rosa bracteata Wendl.). Liquid formulations were applied in bands about 1 cm wide, 1.2 m or more apart, and granule or sphere formulations were applied on the soil surface either broadcast or in rows 1.2 m or more apart. On honey mesquite, karbutilate [tert-butylcarbamic acid ester with 3(m-hydroxy-phenyl)-1,1-dimethylurea] and tebuthiuron {N-[5-(1,1-dimethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} were the most effective herbicides with subsurface spray injections being generally more effective than surface applications. On honey mesquite, differences among row spacing treatments with liquid, granule, or sphere formulations of karbutilate were generally either small or insignificant. Roller chopping reduced the honey mesquite canopy but did not influence the percentage of plants killed by karbutilate at rates of 4.5 kg/ha and below. Bromacil (5-bromo-3-sec-butyl-6-methyluracil), diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], picloram (4-amino-3,5,6-trichloropicolinic acid), prometon [2,4-bis(isopropylamino)-6-methoxy-s-triazine], and 2,3,6-TBA (2,3,6-trichlorobenzoic acid) generally were ineffective as soil treatments for controlling honey mesquite. Of all the herbicides evaluated on Macartney rose, only picloram at 4.5 kg/ha and tebuthiuron at 2.2 and 4.5 kg/ha, as soil treatments, killed a significant number of plants.

The study was conducted to determine the seasonal and diurnal water stress of soybeans [Glycine max (L.) Merr. ‘Lee 74′] grown under intraspecific competition (competition between plants of the same species) and interspecific competition (competition between plants of different species) with common cocklebur (Xanthium pensylvanicum Wallr.). Midday xylem potentials decreased as the season progressed and were lower in common cocklebur during vegetative growth of soybean and in soybean during reproductive growth. For a given species differences in xylem potential due to mode of competition were small. In the diurnal studies xylem potential for each species decreased to a minimum in the early afternoon but recovered to the original pre-dawn values at night. As the season progressed leaf xylem potential (a) decreased at a greater rate, (b) decreased sooner in the day, and (c) recovered at a slower rate. It was shown that differences in xylem potential between soybean and common cocklebur on a given day were small. Greater diffusive resistance values generally were found with soybean than with common cocklebur and with each species grown under interspecific competition.

Hemp sesbania [Sesbania exaltata (Raf.) Cory] was more tolerant to induced moisture stress than soybean [Glycine max (L.) Merr.] with osmotic potentials of −4 and −2 bars, respectively, required to reduce germination. Hemp sesbania germinated at temperatures of 15 to 40 C with optimum germination occurring at 30 to 40 40 C. Seed dormancy was caused by impermeable seed coats. Acid scarification of 45 and 60 min and mechanical scarification 20 and 30 s gave maximum germination. Scarification increased water absorption. Light had no effect on germination. As oxygen content increased from 0 to 21%, germination of unscarified seed increased from 5 to 39%, but germination did not increase as oxygen increased from 21 to 100%. Hemp sesbania and soybean emerged from depths up to 12 cm with maximum emergence occurring at the 1- and 3-cm depths. Hemp sesbania emerged faster and in greater numbers at all depths than soybean.

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.

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.

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.

Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), dinitramine (N4,N4-diethyl-α,α,α-rifluoro-3,5-dinitrotoluene-2,4-diamine), profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro 2,6-dinitro-N-propyl-p-toluidine], fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine], butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine], and USB 3153 (N3,N3-di-N-propyl-2,4-dinitro-6-trifluoromethyl-m-phenylenediamine) were applied to evaluate weed control, cotton (Gossypium hirsutum L. ‘Dunn 119′) tolerance, and effect on rotational crops. Each herbicide was applied at 1-month intervals for 6 months prior to planting at 1, 1.25, 1.5, and 2X the recommended rates. Pigweed (Amaranthus hybridus L. and A. retroflexus L.) population counts and visual control ratings showed that weed control improved when treatments were applied closer to planting. Applications in November and December at 1.25X profluralin, 1.5X trifluralin, fluchloralin, and pendimethalin, 1X USB 3153, and 2X butralin were required to give effective weed control. Spring applications of 1X rates of profluralin, trifluralin, fluchloralin, and USB 3153, 1.25X rates of pendimethalin and dinitramine and 1.5X rate of butralin were required for adequate weed control. USB 3153 at all rates and dates of application severely limited growth and yields of wheat (Triticum aestivum L. ‘Funk 332′) planted after harvest and also the following May. Spring applications of profluralin at 1.5 and 2X rates and trifluralin at the 2X rate resulted in significant injury of rotational sorghum [Sorghum bicolor (L.) Moench ‘Dekalb E-59+’].

The double pot technique was used to study the effects of uptake site of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl—phenyl]-4(1H)-pyridinone} on early shoot and root development of soybean [Glycine max (L.) Merr. ‘Williams’] and cotton (Gossypium hirsutum L. ‘Acala SJ-1′). Soybean is susceptible and cotton is resistant to fluridone. Root uptake in soybean resulted in increased shoot length in the epicotyl and shoot apex, reduced shoot fresh weight, chlorosis of primary and trifoliolate leaves, as well as reduced root length, branching, and fresh weight. Shoot uptake resulted in reduced shoot length above the hypocotyl, reduced shoot weight, severe chlorosis of primary leaves, and inhibition of trifoliolate leaf formation. The reduction in the root length, branching, and weight was less by shoot uptake than by root uptake. In cotton, root uptake resulted in reduced shoot length in the epicotyl and shoot apex, slight reduction in shoot weight, no effect on chlorosis of cotyledon leaves, moderate to slight chlorosis of the true leaves, and no effect on root length, branching, or fresh weight. Shoot uptake resulted in reduced length of all shoot components and shoot weight, chlorosis of cotyledon leaves and the true leaves, and reduced root length, branching, and weight. Compared to soybean, cotton required much higher fluridone concentrations to show the above effects. It was generally concluded that in soybean, uptake by both the root and the shoot contributed significantly to the injury, whereas in cotton, shoot uptake was relatively more important.

Seed germination of Italian thistle (Carduus pycnocephalus L.) and slenderflower thistle (Carduus tenuiflorus Curt.) was rapid and high, with no strong requirements for afterripening. Both species germinated at a wide range of alternating temperatures from −2 to 40 C. Their germination-temperature profiles were similar, with Italian thistle germinating over a slightly wider range of temperatures. The achenes of both species have abundant mucilage. This mucilage, by improving water retention, tended to increase germination on the surface of clay soil.

Field bindweed (Convolvulus arvensis L.) was controlled most effectively when glyphosate [N-(phosphonomethyl)glycine] was applied as a foliar spray to blooming field bindweed. This control resulted in significant yield increases of winter wheat (Triticum aestivum L.). Earlier growth stage treatments were less effective. Dicamba (3,6-dichloro-o-anisic acid), used similarly, controlled field bindweed but caused injury to the following wheat crop. Preharvest treatments of glyphosate in wheat aided harvesting operations and controlled the perennial field bindweed through the summer. Several dinitroaniline herbicides applied as a subsurface layer (SSL), controlled field bindweed for more than 8 months after treatment. However, these treatments caused visible injury and affected the yield of the first crop of wheat but had little effect on a second crop. Dicamba applied SSL at lower rates resulted in excellent field bindweed control.

Environmental control chamber experiments showed that cotton (Gossypium hirsutum L. ‘Stoneville 213′) and soybean [Glycine max (L.) Merr. ‘Bragg’] root and shoot growth were reduced when treated with increasing rates of dinitramine (N4,N4-diethyl-α,α,α-tri-fluoro-3,5-dinitrotoluene-2,4-diamine), profluralin [N-(cyclopropylmethyl)-α,αα-trifluoro-2,6-dinitro-N-propyl-p-toluidine], and trifluralin (α,α,α-trifluoro-2,6-dintrio-N,N-dipropyl-p-toluidine). Viusal root ratings, dry root weights, and fresh and dry herbage weights were used to evaluate plant response to herbicide treatments in environmental chambers. The order of increasing GR50 values for cotton on two soils and with all response measurements, except dry root weights on one soil, was trifluralin, dinitramine, and profluralin. The order of increasing GR50 values for soybeans on two soils and with all response measurements was dinitramine, trifluralin, and profluralin.

August and October applications of glyphosate [N-(phosphonomethyl)glycine] and paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) were compared at two rates for pasture renovation. During the 2 yr of the experiment, sod suppression was frequently greater with October applications than with August applications. Medium red clover (Trifolium pratense L.) became established in all the plots, and density and yield tended to increase as grass suppression increased.

Glyphosate was compared over a 3-yr period with an ester of 2,4-D [(2,4-dichlorophenoxy)acetic acid] and picloram (4-amino-3,5,6-trichloropicolinic acid) for control of tall ironweed (Vernonia altissima Nutt.) when applied in August. Picloram killed from about 80 to 100% of the tall ironweed plants and was superior to 2,4-D. Glyphosate was inconsistent for controlling tall ironweed but could be used for killing perennial weeds as well as sod suppression.