Young orange [Citrus sinensis (L.) Osbeck ‘Pineapple sweet orange’] trees are more sensitive to bromacil (5-bromo-3-sec-butyl-6-methyluracil) than young mandarin (Citrus reticulata Blanco ‘Cleopatra mandarin’) trees. Pineapple sweet orange roots absorbed twice as much 14C from bromacil, and accumulated three times as much in the leaves, as did Cleopatra mandarin. The amount of conjugated metabolites formed was the same in the roots of the two cultivars, but twice as much formed in the leaves of Cleopatra mandarin as in the leaves of Pineapple sweet orange. The principle metabolite was 5-bromo-3-sec-butyl-6-hydroxymethyluracil; a minor metabolite was tentatively identified as 5-bromo-3-(3-hydroxyl-1-methylpropyl)-6-methyluracil. No 5-bromouracil was detected. Citrus cultivars differ in their ability to accumulate and metabolize bromacil into conjugated nonphytotoxic compounds.

The unicellular green alga, Chlorella sorokiniana Shihira and Krauss, was cultured in vitro using an inorganic growth medium with various concentrations of the herbicide glyphosate [N-(phosphonomethyl)glycine]. Growth rates, in terms of ceil doublings per day, were determined for cells inoculated into media containing from 5.91 × 10−6 M to 591 × 10−6M glyphosate. Comparisons with a control, which supported 10.4 doublings/day, showed growth only slightly reduced at 5.91 × 10−6M and 11.8 × 10−6M, with averages of 9.7 and 9.5 doublings/day; reduced by more than half at 17.7 × 10−6M with an average of 4.4 doublings/day; and prevented at all higher concentrations. In addition to completely preventing growth at 23.7 × 10−6M and above, glyphosate seemed to cause a deterioration of the inoculum cells. Filtering the media containing 5.91 × 10−6M, 11.8 × 10−6M, and 17.7 × 10−6M through kaolinite prior to introduction of the alga reduced the inhibition previously noted at 17.7 × 10−6M and resulted in growth rates from 9.1 to 9.5 doublings/day.

Greenhouse pot experiments were conducted to study the effect of various levels of nitrogen, applied as ammonium nitrate (NH4NO3) and ammonium sulfate [(NH4)2SO4], on hemp broomrape (Orobanche ramosa L.) infestation on tobacco (Nicotiana tabacum L. ‘Jordan 1’) and tomato (Lycopersicon esculentum Mill. ‘Caludia Raf’). Infestation of tobacco and tomato by hemp broomrape was drastically reduced as higher levels of both fertilizers were applied. However, the dry weights of roots and shoots of both crop plants, as well as tomato yield, were reduced when NH4NO3 was applied at 50 g/pot, and when (NH4)2SO4 was applied at higher than 60 g/pot. In a separate pot experiment in the field, hemp broomrape infestation on tomato was drastically reduced, and tomato shoot dry weight, as well as tomato yield, were increased when (NH4)2SO4 was applied at higher than 40 g/pot as 20-g increments repeated at 10-day intervals compared to those of the control.

Oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] applied early enough for large crabgrass [Digitaria sanguinalis (L.) Scop.] control provided full season goosegrass [Eleusine indica (L.) Gaertn.] control during bermudagrass [Cynodon dactylon (L.) Pers. ‘Midiron’ and ‘Tufcoat’] establishment from sod strips. Prosulfalin {N-[[4-(dipropylamino)-3,5-dinitrophenyl]sulfonyl]-S,S-dimethylsulfilimine}, DCPA (dimethyl tetrachloroterephthalate), pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] and bensulide [0,0-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] gave full season goosegrass control in well-established Midiron bermudagrass, but not during the initial establishment period where open bare soil was present. Napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] provided long term residual control of goosegrass with some interference with rooting of bermudagrass from stolon nodes. Winter survival of Midiron bermudagrass was superior to Tufcoat bermudagrass. Controlling annual grasses permitted superior bermudagrass growth, and winter survival was improved tremendously. Postemergence goosegrass control was obtained with MSMA (monosodium methanearsonate) and methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] when repeated several times during the season. A mixture of MSMA and methazole was superior to either used alone. The rate of bermudagrass establishment was increased through the control of goosegrass with herbicides.

As a result of applying arsenicals as herbicides, desiccants, or soil sterilants, soil As levels can increase under some conditions. Three arsenicals, sodium arsenite, (NaAsO2), cacodylic acid, (hydroxydimethylarsine oxide), and MSMA (monosodium methanearsonate) were applied to bare soil at 1, 2, and 10 times the recommended maximum application rates. After incorporation, radishes (Raphanus sativus L.) and soybeans [Glycine max (L.) Merr.] were planted as indicator crops to assess the phytotoxicity of accumulated soil As residues. Soil As residues increased at all levels of application. However, only 50% of the As applied at 10 times the recommended rate was found after seven annual applications, regardless of the source. Total losses of As from the soil averaged 14 to 15% of that applied each year. At 10 times the recommended rate, As generally reduced radish and soybean yields, but seldom reduced yields at the two lower rates. Results indicated little danger of As residue accumulating to phytotoxic levels under normal application rates.

Plots of western false hellebore (Veratrum californicum Durand), treated in 1968 and 1969 with 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 2.2 kg/ha, were reexamined in July 1979 to determine vegetative changes, especially any increases in the production of desirable species and long-term control of western false hellebore. Grass, sedge, and rush production had doubled, and broadleaved plant production, excluding western false hellebore, which was eliminated, decreased on treated plots. Western false hellebore had not reinvaded the treated plots; control remained at 100% for 10 yr. Removal of the western false hellebore on treated plots allowed an increase in grass, sedge, and rush production of 1,500 kg/ha over check plots.

Absorption coefficient (k), infinite reflectance (Ri), and scattering coefficient (s) were tabulated for five wavelengths and analyzed for statistical differences for seven weed species. The wavelengths were: 0.55 μm, 0.65 μm, 0.85 μm, 1.65 μm, and 2.20 μm. The Ri of common lambsquarters (Chenopodium album L.), johnsongrass [Sorghum halepense (L.) Pers.], and annual sowthistle (Sonchus oleraceus L.) leaves at the 0.85-μm wavelength were significantly (p = 0.05) higher than for sunflower (Helianthus annuus L.), ragweed parthenium (Parthenium hysterophorus L.), or London rocket (Sisymbrium irio L.). Annual sowthistle had the largest k value, and Palmer amaranth (Amaranthus palmeri S. Wats.) had the smallest k value at the 0.65-μm chlorophyll absorption wavelength. In general, johnsongrass, ragweed parthenium, or London rocket had the largest s values among the five wavelengths, whereas annual sowthistle and Palmer amaranth were usually lowest.

Information from taxonomic treatments and comparisons of accessions from numerous locations grown in the field and greenhouse were combined and summarized to produce a key and descriptions of common agricultural nightshades in North America (Solanum americanum Mill., S. nigrum L., S. ptycanthum Dun., and S. sarrachoides Sendt.). Quantitative and qualitative descriptions of key characters and photographs of important morphological structures are provided to facilitate field identification. Problems with nomenclature among these species are discussed, and a system of common names that would standardize usage is proposed.

Postemergence applications of MSMA (monosodium methanearsonate) for weed control in spring wheat (Triticum aestivum L.) were evaluated in the field, greenhouse, and controlled environmental chamber. MSMA controlled weeds better when applied to wheat at the four- to five-leaf stage than when applied at the two- to three-leaf stage. MSMA, tank mixed with barban (4-chloro-2-butynyl-m-chlorocarbanilate) or diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}, controlled wild oat (Avena fatua L.), green foxtail, [Setaria viridis (L.) Beauv.] and broadleaf weeds better than did MSMA applied alone. Wild oat control with tank-mix applications of MSMA and difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) was variable. Weed control with MSMA was enhanced by 30 C air temperatures, 90% relative humidity, and adequate soil moisture. A simulated rainfall of 0.5 mm within 0.5 h or 4 mm with 4 hr after application reduced wild oat control with MSMA.

Photosynthesis in corn (Zea mays L. ‘Pioneer 3369A’) was inhibited 25% by atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] after a 2-h root exposure in nutrient solution. Photosynthesis of the treated plants had completely recovered 21.4 h after removal from the treatment solution. Recovery of photosynthesis from second and third successive atrazine treatments required only 10.3 h and 4.0 h, respectively. Atrazine metabolism rates in corn plants after 1, 2, or 3 successive 4-h treatment periods, where each treatment period was followed by a 12-h recovery period, showed increased rates of metabolism of atrazine during each recovery time. An increased level of glutathione-S-atrazine was found following the first 4-h atrazine treatment and 12-h recovery. The enhanced production of GS-atrazine was maintained throughout subsequent exposures and recoveries. An inverse correlation (r2 = 0.992) was found between the increase in GS-atrazine production following each 4-h atrazine exposure and the time required for corn plants to recover from atrazine-induced photosynthesis inhibition. Enhanced detoxification of atrazine by corn plants pretreated with atrazine was indicated. No enhanced tolerance to other herbicides was observed from atrazine pretreatment. This phenomenon is similar to that described for the enhanced detoxification of several insecticides in animal systems.

Greenhouse and field experiments (at Rosemount and Roseau, Minnesota) were conducted to characterize the growth and development of 10 quackgrass [Agropyron repens (L.) Beauv.] biotypes selected near Roseau, Minnesota. The biotypes were highly variable for all traits studied. Eight of the biotypes had flag leaves approximately 1 cm wide, but two biotypes had flag leaves approximately 1.5 cm wide. Four biotypes were glaucous and blue-green in color, and the other biotypes varied from light to dark green and had varying leaf pubescence. In the field, plant height varied from 59 to 79 cm, and rhizome length varied from 105 to 135 cm. Spike production varied from 4 to 62 spikes per plant, and mid-season rhizome bud production varied from 246 to 1,211 buds, suggesting that the biotypes varied in their reproductive potential. Shoot dry weight varied from 48 to 362 g per plant, and daughter shoot production varied from 7 to 235 shoots per plant. The quackgrass near Roseau, Minnesota, appears to be made up of several distinct biotypes.

The effects of caffeic acid, chlorogenic acid, t-cinnamic acid, p-coumaric acid, ferulic acid, gallic acid, p-hydroxybenzaldehyde, 5-sulfosalicylic acid, vanillic acid, and vanillin on growth, photosynthesis, water relations, and chlorophyll content of 3-week-old soybeans [Glycine max (L.) Merr. ‘Tracy’] grown in aerated nutrient solution were determined. At concentrations of 10−3 M, caffeic, t-cinnamic, p-coumaric, ferulic, gallic, and vanillic acids significantly reduced dry matter production, leaf expansion, height, leaf production, net assimilation rate (rate of dry matter production per unit leaf area), and leaf area duration (total leaf area present during treatment interval). Chlorogenic acid, p-hydroxybenzaldehyde, 5-sulfosalicylic acid, and vanillin at 10−3 M did not inhibit growth. None of the 10 compounds at 10−4 M inhibited growth. At concentrations of 10−3 M, caffeic, t-cinnamic, p-coumaric, ferulic, gallic, and vanillic acids severely reduced net photosynthetic rate and stomatal conductance of single, fully expanded leaves. These same compounds also caused marked reductions in leaf chlorophyll content, with net losses of chlorophyll occurring over an 86-h period after treatment.

The effects of buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} on the photochemical reactions of isolated pea (Pisum sativum L.) chloroplast thylakoids were analyzed. Buthidazole was found to inhibit electron transport at two distinct sites in the photosynthetic electron transport chain. The major site of inhibition was on the reducing side of photosystem II at the site of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] inhibition. Buthidazole also had a secondary site of electron transport inhibition on the oxidizing side of photosystem II. No evidence was found for buthidazole to act as an uncoupler or as an energy transfer inhibitor.

Visible wheat (Triticum aestivum L.) injury, delay in bloom date, and yield reduction were observed following herbicide treatments in growing wheat. Protein content and volume weight of winter wheat were not significantly affected by any herbicide treatment. Some treatments reduced annual grass and broadleaf population by 90% or more 6 weeks after spraying and maintained weed control 8 weeks in untilled winter wheat stubble. Effective herbicide treatments that caused the least winter wheat injury in 1977 and 1978 included metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] + alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 0.3 + 2.8 kg/ha, metribuzin + oryzalin (3,5-dinitro-N 4,N 4-dipropylsufanilamide) at 0.3 + 1.8 kg/ha, metribuzin + pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] at 0.3 + 2.2 kg/ha, metribuzin + SN-533 [N-ethyl-N-propyl-3-(propylsulfonyl)-1H-1,2,4-triazole-1-carboxamide] at 0.3 + 0.8 kg/ha, and R-40244 [1-m-trifluoromethylphenyl)-3-chloro-4-chloromethyl-2-pyrrolidone] at 1.1 kg/ha. Herbicide treatments that showed the most potential to control annual grass and broadleaf weeds selectively in tillered winter wheat and stubble in 1978 include metribuzin + metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 0.3 + 2 kg/ha, metribuzin + oryzalin at 0.3 + 1.4 kg/ha, and metribuzin + pendimethalin at 0.3 + 2 kg/ha.

A simple and quick method is described for identifying biotypes of common groundsel (Senecio vulgaris L.), common lambsquarters (Chenopodium album L.), and smooth pigweed (Amaranthus hybridus L.) that are resistant or susceptible to triazine herbicides. Leaf discs (3 mm diam) from the tested plants were vacuum infiltrated with a phosphate medium and exposed to a 3-klux light source. When 1.0 × 10−5M and higher levels of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) were present, the leaf discs from susceptible biotypes failed to float to the surface, whereas the leaf discs from resistant biotypes floated within 1 h. The urea herbicide, fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] inhibited the floating of leaf discs from both the triazine-susceptible and triazine-resistant biotypes. This method can be used to evaluate large numbers of plants to determine if they are resistant or susceptible to triazines without destroying the plants or preventing seed production.

Several herbicides were sprayed on emerged London rocket (Sisymbrium irio L.), common sunflower (Helianthus annuus L.), ragweed parthenium (Parthenium hysterophorus L.), annual sowthistle (Sonchus oleraceus L.), and onion (Allium cepa L. ‘yellow granex PRR’), to determine selectivity. Onion yields were reduced with common sunflower and London rocket interference within 7 weeks after emergence. Oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] at 2.2 kg/ha controlled all but common sunflower under most field conditions and reduced the yield of onion in one experiment out of six. Methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] and bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) reduced the yields of onion in two of four experiments and three of six experiments, respectively. Both herbicides controlled most weed species, but only bromoxynil controlled annual sunflower adequately. Onion was injured when low temperature, low light intensity, and high relative humidity occurred within 3 days of the application of herbicides. Bioassays showed that oxadiazon persisted 5 months in soil in three of five experiments. Seeded London rocket populations reduced the growth of onion 20% within the first 4 weeks and 65% within 12 weeks after planting.

Glyphosate [N-(phosphonomethyl)glycine] toxicity to bermudagrass [Cynodon dactylon (L.) Pers.] increased as 0.84 kg/ha of the herbicide was applied in decreasing volumes of diluent from 374 to 47 L/ha. Visible injury to bermudagrass varied from 18 to 91% depending upon the spray solution formulation and diluent volume. The addition of surfactant to glyphosate (MON 0139) formulated without surfactant increased bermudagrass injury at each diluent volume tested. Glyphosate commercially formulated with surfactant (MON 2139) was the most toxic of the three formulations to bermudagrass. Regrowth of bermudagrass clipped at the soil surface 48 h after treatment ranged from 10% of the untreated control with MON 2139 at 47 L/ha to 100% of the control with MON 0139 at 374 L/ha. The MON 2139 formulation showed as much as a six-fold increase in foliage regrowth when the diluent volume was increased from 47 to 374 L/ha.

Mechanical scarification of burcucumber (Sicyos angulatus L.) seeds resulted in increased water absorption and germination. Burcucumber germination occurred at temperatures ranging from 15 to 35 C with optimum germination occurring from 20 to 30 C. Scarified burcucumber seeds were more sensitive to simulated moisture stress than were either soybean [Glycine max (L.) Merr. ‘Williams’] or corn [Zea mays L. ‘Pioneer Brand 3369A’]. Regardless of osmotic potential, intact burcucumber seeds did not germinate; scarified seeds germinated at osmotic potentials to −6 bars. Cold stratification at 4 C for 18 weeks modified seedcoat permeability so that 11% of non-scarified burcucumber seeds germinated. Increasing depth of planting decreased emergence with limited emergence occurring at depths of 15 and 16 cm in field and growth chamber studies, respectively.

Absorption and translocation of 14C-metriflufen {2-[4-(4-trifluoromethylphenoxy)phenoxy] propanoic acid} in johnsongrass [Sorghum halepense (L.) Pers.] and soybean [Glycine max (L.) Merr. ‘Lee 68’] were evaluated under different environmental conditions. At 40% relative humidity (RH), an increase in air temperature from 18 to 35 C increased translocation of the 14C in johnsongrass more than four-fold following application of 14C-metriflufen to an area on the third leaf. At 100% RH, translocation of the 14C was twice as great at 27 C as at 18 C, but translocation at 35 C was intermediate. In the combined analysis, translocation in johnsongrass was no better at 100% RH than at 40% RH. Regardless of level of RH, most translocation in johnsongrass at 18 and 27 C was toward the distal half of the treated leaf, but at 35 C most translocation was toward the proximal half of the treated leaf. Translocation of 14C in soybeans increased more than four-fold as air temperature was increased from 18 C to 35 C, and more translocation occurred at 100% RH than at 40% RH at 18, 27, and 35 C. More than 80% of the 14C-metriflufen remained in the treated leaf or on the surface of treated soybean leaves 48 h after application. More of the applied radioactivity was recovered from soybean plants than from johnsongrass plants.

An electrical discharge system (EDS) was evaluated in field studies conducted in 1977 through 1979 in western Nebraska for its ability to control weed escapes in sugarbeets (Beta vulgaris L. ‘Mono Hy D2′). Nine weeks after sugarbeets were planted, kochia [Kochia scoparia (L.) Schrad.] had attained a height above sugarbeets sufficient for EDS treatment. Redroot pigweed (Amaranthus retroflexus L.) and common lambsquarters (Chenopodium album L.) generally attained sufficient height above sugarbeets 11 and 13 weeks after sugarbeet planting. Sugarbeet root yields were reduced 40, 20, and 10% from competition by kochia, common lambsquarters, and redroot pigweed, respectively. Treatment of kochia, redroot pigweed, and common lambsquarters with EDS in some cases resulted in a reduction in weed height. The EDS treatments reduced the stand of all weeds 32, 39, and 47% for 1977, 1978, and 1979, respectively. Although the EDS treatments failed to kill many weeds, it did suppress the competitive ability of the three weeds to the extent that sugarbeet yields were higher in areas receiving EDS treatments than areas receiving no EDS treatment.