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.

Diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine], and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) were applied pre-plant in safflower (Carthamus tinctorius L. ‘AC-1′) for 6 yr at two locations. Diuron and prometryn reduced crop stands in 2 of 6 yr on the sandier soil at Mesa. Growth of sorghum [Sorghum bicolor (L.) Moench ‘Amak R-10′] in the greenhouse in soil collected 10 months after each herbicide application was reduced by 1.7 kg/ha of trifluralin in 3 of 6 yr in the Yuma silty clay loam and by both rates of trifluralin in 1 of 6 yr in the sandier soil at Mesa. Growth of barley (Hordeum vulgare L. ‘Arivat’) was not reduced in soil treated with any herbicide at either location. Herbicides did not accumulate in winter-planted safflower.

Seventy-three rice (Oryza sativa L.) cultivars and uniform advanced-generation dwarf lines were evaluated for their response to molinate (S-ethyl hexahydro-1H-azepine-1-carbothioate) at concentrations of 0, 1, 2, and 4 ppmw in a 7-day laboratory screening test. These rice entries varied significantly in their response to each molinate concentration when shoot height of each entry was compared to that at the 0 ppmw level. Entries were ranked according to their molinate response at the 2 ppmw concentration and categorized as being either tolerant, intermediate or susceptible. Entries categorized as susceptible at 2 ppmw were further subdivided into highly susceptible and moderately susceptible categories based on their response to the 1 ppmw concentration. Those categorized as tolerant at the 2 ppmw concentration were likewise divided into highly tolerant and moderately tolerant categories on the basis of their response to the 4 ppmw concentration. The results of this bioassay indicates the possible existence of a genetically inherited response to molinate which might be manipulated by plant breeders to develop cultivars which have a high tolerance to molinate.

Concentrated sulfuric acid (H2SO4) scarification of balloonvine (Cardiospermum halicacabum L.) for 3 h reduced balloonvine seed coat thickness by 25%, and resulted in increased water absorption and maximum germination. Germination of balloonvine occurred at temperatures of 15 to 40 C with optimum germination occurring at 35 C. Intact balloonvine seed was more sensitive to simulated moisture stress than soybean [Glycine max (L.) Merr. ‘Bragg’]. No balloonvine germination occurred at osmotic potentials of −2 bars and less with intact seeds. Balloonvine seed with seed coats removed germinated at osmotic potentials of −8 bars. Maximum emergence of balloonvine occurred at the 1- and 3-cm depths with limited emergence at a depth of 12 cm.

Other research has shown that a roller applicator can selectively control weeds that protrude above the crop, conserve over 80% of the herbicide, eliminate spray drift and splash, and obviate recirculation of the spray solution. The carpet on the roller applicator must be moist enough to transfer ample herbicide to the weeds it contacts but dry enough to prevent dripping of herbicide solution from the carpet. An electronic moisture sensor and solenoid valve system was designed to permit operation of the roller applicator through various weed densities while automatically maintaining a proper level of herbicide solution in the carpet of the roller.

Six crop species were irrigated with water that contained up to several times more glyphosate [N-(phosphonomethyl)glycine] than would be expected in irrigation water as a result of spraying ditchbank vegetation. In June or July 1976, sugarbeets (Beta vulgaris L.), alfalfa (Medicago sativa L., ‘Vernal’), grain sorghum [Sorghum bicolor (L.) Moench], field beans (Phaseolus vulgaris L., ‘Pinto’), tomatoes (Lycopersicon esculentum Mill., ‘Roza’), and squash [Cucurbita moschata (Duch.) Duch. ex Poir.] were sprinkler-irrigated with water that contained glyphosate at 0, 0.02, 0.22, or 2.2 ppmw. These concentrations were applied continuously for 8 h to make total applications of 0, 0.01, 0.1, and 1.1 kg/ha, respectively. No injury symptoms developed in any of the crop plants. Yields of treated crops were equal to those produced by untreated plants.

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.

For 3 yr, herbicide treatments of preplant trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), postemergence diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], both herbicides, or none were superimposed on cotton (Gossypium hirsutum L. ‘Acala SJ-2′) grown on beds centered at 102 cm using a single row or two rows spaced 28 cm apart. Cotton stand, after thinning, was 5.1 plants/m in each cotton row. Herbicides controlled annual weeds regardless of planting pattern. Cultivation, without herbicides, controlled annual grass weeds much better in cotton grown in single rows than in double rows. Preplant applications of trifluralin did not influence populations of cotton plants, regardless of row pattern. Single- and double-row plots treated with trifluralin always yielded more than untreated double rows. In two of three seasons, however, single-row plots without herbicides yielded as much as those treated with trifluralin. The lower yields in the double-row cotton were associated with reduced annual grass control especially in plots not treated with trifluralin. Weed control treatments or planting patterns did not influence the occurrence of Pythium ultimum Trow or Rhizoctonia solani Kühn on cotton seedlings. The presence of Thielaviopsis basicola (Berk & Br.) Ferr. on cotton seedlings was not influenced by planting pattern but was increased by trifluralin in the third year of the study. Percentage of cotton plants with symptoms of verticillium wilt (Verticillium dahliae Kleb.) was not influenced by weed control treatments, but the percentage of diseased plants was higher in single-row than in double-row planting patterns. We attribute this response to fewer plants per hectare in single rows compared to double rows.

To estimate the potential growth and distribution of itchgrass (Rottboellia exaltata L. f.) in the United States, we grew the plant in 36 combinations of day and night temperatures in controlled-environment greenhouses. Day temperatures ranged from 17 to 32 C and night temperatures from 11 to 26 C. Total dry weights, leaf areas, heights, and numbers of tillers were determined at 3, 31, and 58 days after emergence. Mathematical growth analysis techniques were used to calculate net assimilation rates (NAR) and leaf area durations (LAD). Maximum dry matter production (the product of NAR and LAD) and maximum leaf area production occurred at 32/26 C. Dry matter production and leaf area production were greatly reduced by day temperatures below 29 C and night temperatures below 23 C. The retardation of dry matter production by low night temperature was due mainly to reductions in LAD rather than to reductions in NAR. Low day temperatures reduced dry matter production through combined effects on LAD and NAR. At the warmer day temperatures, tiller production increased with decreasing night temperature. Flowering occurred at all day temperatures and at all night temperatures of 14 C or greater. Based on its growth responses to temperature, itchgrass would reach 75 to 100% of its maximum potential growth in the Gulf Coast states, the lower Midwest, the South Atlantic states, and the Southwest. Therefore, it represents a serious potential weed problem in these regions.

An oat (Avena sativa L. ‘Dal’) primary root bioassay procedure was used to study the persistence of eight dinitroaniline herbicides in soil. Sensitivity of the bioassay to the herbicides depended on the length of time roots were exposed to the herbicide treatments. Root inhibition increased with time of exposure. Herbicide persistence was studied under growth chamber, greenhouse, and field conditions. The herbicides remained biologically active the longest under dry and cool soil conditions. At 5 C, little change in herbicide activity was observed over an 8-month period. Under greenhouse conditions, the herbicides in wet soil dissipated rapidly, as compared with those in dry soil. Soil samples taken from depths of 0 to 7.5 cm and from 7.5 to 15 cm in the field showed that the herbicides were retained primarily in the surface 7.5 cm. Small amounts were found from 7.5 to 15 cm only shortly after the herbicides were applied. Dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) was the only herbicide tested of which soil residues from spring field applications were not detected the following fall.

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.

Field and greenhouse studies were conducted to determine the degree to which annual bluegrass (Poa annua L.) could be controlled by inhibiting seedheads. The materials used were: MH (1,2-dihydro-3,6-pyridazinedione); chlorflurenol (methyl 2-chloro-9-hydroxyfluorene-9-carboxylate), plus methyl 9-hydroxyfluorene-9-carboxylate, and methyl 2,7-dichloro-9-hydroxyfluorene-9-carboxylate; and endothall [7-oxabicyclo (2.2.1) heptane-2,3-dicarboxylic acid]. The effects of these materials on pollen quality and the viability of seed produced by treated plants were also determined. For all chemicals used, multiple applications at low rates resulted in better seedhead inhibition than single treatments at higher rates and their effects lasted longer. However, treatments that inhibited seedheads by an amount predicted to reduce annual bluegrass (more than 75%) often caused objectionable foliar discoloration. Endothall, particularly the granular formulation, caused excessive injury at all rates. All growth regulators reduced the number of seed produced, which affected the number of seeds that germinated from soil that was taken from treated plots. The number of seed found in the soil was sufficient to allow the stand to be self-perpetuating. All treatments reduced the percentage of fertile pollen, however, this reduction was not significant because the germination of seed harvested from treated plants was not reduced significantly. Even though these treatments reduced seedheads significantly, the population of annual bluegrass the following year was not reduced.

Adsorption of benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), 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], oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide), profluralin [N-(cyclopropylmethyl)-α,α,α-tri-fluoro-2,6-dinitro-N-propyl-p-toluidine], and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) was studied in 10 Wisconsin soils. Ratios of the quantity of each herbicide adsorbed and quantities remaining in the soil solution at equilibrium (Kd value) on a Piano silt loam (Typic Argiudoll fine-silty, mixed, mesic) remained relatively constant over a range of concentrations. Herbicide adsorption by the soils was related more closely to soil organic matter than to the other soil chemical and physical properties. Diffusion of the herbicides in Piano silt loam was affected by soil water. Diffusion of trifluralin, profluralin and benefin decreased as soil water increased. Diffusion of dinitramine and fluchloralin did not change significantly with change in water content. Diffusion of oryzalin increased at the highest soil water content. None of the herbicides moved more than 10 mm in the soil during a 17-day period. In unsaturated Piano silt loam, relative mobility of the herbicides was trifluralin ≥benefin>profluralin>fluchloralin>dinitramine≥oryzalin. Oryzalin reached highest mobility in water-saturated soil.

The influence of weed removal, cultivar, and row spacing on soybean [Glycine max (L.) Merr.] yields was determined for 3 yr at the western edge of the soybean production area in the Great Plains in order to establish the critical weed-control periods. Early weed removal aided soybean stand establishment, and there was an inverse relationship between soybean stand and production of weed top-growth. Soybean seed weight and numbers per plant both increased as weed growth decreased. The soybean variety ‘Amsoy 71’ was more competitive than ‘Beeson’ to both early and late emerging weeds. Soybeans weeded at 2 through 4 weeks after planting did not show significantly reduced soybean yields from later emerging weeds. Thus, weed control the first month after planting is the most critical in obtaining high soybean yields.

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.

The influence of soil moisture on wild oat control from soil-incorporated methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)-phenoxy] propanoic} was determined in the greenhouse. Wild oat control with soil-incorporated diclofop at 1.5 or 3 ppmw increased linearly when soil moisture in a Tiffany sandy loam increased from 18.5 to 23.5% (75% to 125% of field capacity). The efficacy of soil-incorporated diclofop was not reduced when soil moisture was allowed to decrease from 21 (field capacity) to 18.5, 16, 13.5, or 11% (wilting point) before rewatering to 21%. The soil moisture level at the time of herbicide application determined the degree of wild oat control with soil-incorporated diclofop. Wild oat control with diclofop increased when a Tiffany sandy loam with 16% moisture (50% of field capacity) at the time of herbicide application, was watered to field capacity after 8 or 12 days delay, and control did not change with watering to field capacity at the time of herbicide application or when delayed 4 or 16 days. The movement of 14C-diclofop in soil columns was greater within coarse than fine textured soils and increased with water volumes applied, regardless of soil type. Further, the leachability of 14C-diclofop was two and a half times greater than that of 14C-trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine).

The rate of herbicide required to reduce growth of grain sorghum (Sorghum vulgare, Per. ‘Pioneer 8417′) by 50% (GR50) and soil adsorption coefficients (Ka) were determined for the experimental herbicide, fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone}, in 14 soils. A linear correlation analysis was conducted between GR50 values and the chemical and physical properties and fluridone absorption coefficient (Ka) for 14 soils. The GR50 values were significantly correlated to soil organic matter and Ka. A stepwise regression analysis suggests that Ka or organic matter content can be used to predict the rate of fluridone application required for herbicidal activity.

The experimental herbicide R-24191 [1-(m-t-butylacetamidophenyl)-3-methyl-3-methoxy urea] inhibited growth of Chlorella sorokiniana Shihira and Kraus, O2 evolution during CO2 fixation by Chlorella and isolated leaf cells of spinach (Spinacia oleracea L. ‘Winter Bloomsdale 769′), the photoreduction of NADP by isolated chloroplasts using water or hydroxylamine as the electron donor, the photoreduction of 2,6-dichloroindophenol by isolated chloroplasts, and O2 uptake by isolated chloroplasts using paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) as the electron acceptor. The phenylurea herbicide had no effect on the last reaction when ascorbate plus 2,6-dichloroindophenol were used as the electron donor. The results indicate that the site of the phenylurea inhibition was in photosystem II between water-splitting and photosystem I.

Redroot pigweed (Amaranthus retroflexus L.) and robust foxtail [Setaria viridis (L.) Beauv. var. robusta-alba Schreiber (RWF) or Setaria viridis var. robusta-purpurea Schreiber (RPF)] were investigated regarding their ability to interfere with soybean [Glycine max (L.) Merr. ‘Amsoy 71′] at different weed densities and soybean row spacing throughout two growing seasons. Final weed densities for each species tended to reach a common value because of intraspecific interference regardless of the initial density. With cultivation, a narrow soybean row spacing (38 cm) resulted in less weed growth than did a wide row spacing (76 cm) but with no cultivation, the trend was reversed. Soybeans provided less interference to foxtail than to pigweed during both growing seasons. Interference from foxtail adversely affected soybean yield components and soybean seed yield more than did pigweed interference. Water-stress conditions in 1976 increased the intensity of weed interference and reduced soybean seed yield more severely than in 1975 when moisture was adequate throughout the growing season.

All land uses in eastern and southeastern Nebraska were infested to some extent with hemp dogbane (Apocynum cannabinum L.). The highest infestations were observed in oats (Avena sativa L.) and soybeans [Glycine max (L.) Merr.] and the lowest infestations were in alfalfa (Medicago sativa L.), pastures, and winter wheat (Triticum aestivum L.). Yield reductions from hemp dogbane infestations ranged from 0 to 10% in corn (Zea mays L.), 28 to 41% in soybeans, and 37 to 45% in sorghum [Sorghum bicolor (L.) Moench]. Emergence of hemp dogbane from crown roots occurred when the soil temperature was 17 to 19 C, during April in 1977 and 1978. Plants attained the bud stage within 4 to 7 weeks after emergence. Early flower, full bloom, and pod initiation occurred subsequently at about 1 week intervals. Seeds produced were first viable 10 weeks after full bloom. Root activity or regenerative capacity as measured by length and number of new shoots and roots produced at monthly intervals in the germinator showed a cyclic pattern. The highest activity occurred in the spring and late fall and lowest activity in summer and early fall. Protein levels in the roots ranged from 7 to 9% in the fall and spring to 4 to 5% during the summer. Percentage total nonstructural carbohydrates (TNC) ranged from 20 to 31% in lateral roots and 32 to 53% in crown roots, but there was not a consistent cyclic pattern of percentage TNC during the growing season.