Johnsongrass [Sorghum halepense (L.) Pers.] and soybeans [Glycine max (L.) Merr. ‘Lee 68’] were treated over-the-top with glyphosate [N-(phosphonomethyl)glycine] at 0.2 and 0.4 kg/ha with surfactant in spray solutions and 0.4 and 0.7 kg/ha without surfactant in spray solutions. Treated plants were maintained in the growth chamber for 2 weeks after treatment at 24, 29, and 35 C; 45 and 100% relative humidity (RH); and 12 and 20% soil moisture. Glyphosate at 0.4 kg/ha applied without surfactant controlled johnsongrass better at 100% than at 45% RH. Johnsongrass control was better with 20% than with 12% soil moisture. Averaged over all evironments, the order of glyphosate toxicity to johnsongrass at 0.4 and 0.7 kg/ha was 35 C > 29 C > 24 C. The environmental condition of 45% RH and 12% soil, moisture resulted in least johnsongrass control regardless of temperature. The order of glyphosate toxicity to soybeans when applied without surfactant was 24 C > 29 C > 35 C. Glyphosate applied without surfactant was more toxic to soybeans at 100% than at 45% RH and more toxic at 12% than at 20% soil moisture. Surfactant in spray solutions increased glyphosate toxicity to johnsongrass and soybeans.

The experimental herbicide EMD-IT 5914 [difunon, 5-dimethyl-amino-methylene-2-oxo-4-phenyl-2,5-dihydrofurane-carbonitrile-(3)] was applied to unicellular algae and its effect on growth, oxygen evolution and photosynthetic electron transport measured. Inhibition of biosynthesis of chloroplast pigments was evaluated in relation to the activities of porphobilinogenase and δ-aminolevulinic acid dehydratase. The only direct effect of the herbicide was an inhibition of carotenoid biosynthesis but not of photosynthetic electron transport or enzymic activities connected with porphyrin biosynthesis. Chlorophyll bleaching is considered to be a secondary process.

Applications of glyphosate [N-(phosphonomethyl)glycine] to the leaves of pea (Pisum sativum L. ‘Burpee's Blue Bantam’), sunflower (Helianthus annuus L. ‘Mammoth’), and bean (Phaseolus vulgaris L. ‘Red Kidney’) reduced transpiration in all three species. The reduction varied with species and concentration applied. Eight-day-old bean leaves responded earlier than leaves on older plants. However, after 29 h, there was no difference in transpiration rates with seedling age, since treated leaves on both ages investigated were transpiring at about one-half the rate of control leaves. Addition of surfactant to the solution shortened the time interval between treatment and transpirational response but did not affect the final transpiration rate as compared to glyphosate without surfactant. The effect of glyphosate on transpiration was not due to changes in water availability or to the surface of the leaf that was treated. It is suggested that these results can give some insight into uptake, translocation, and mode of action of glyphosate.

Enzymatically isolated mesophyll cells of soybean [Glycine max (L.) Merr. ‘Kino’] and cotton (Gossypium hirsutum L. ‘Stoneville 1613 glandless’) were used to study the effects of three surfactants, I = ‘Sterox SK’ (polyoxyethylene thioether), II = ‘Renex 36’ (polyoxyethylene-6-tridecylether), and III = ‘WSCP’ [polyoxyethylene (dimethylimino) ethylene (dimethylimino) ethylene dichloride] alone or in combination with two herbicides, D-497 (1,1-dimethyl-4,6-diisopropyl-5-indanylethyl ketone) and oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) on cell permeability, photosynthetic 14CO2 fixation and cellular ultrastructure. Greatest amount of efflux of 14C-labeled material from soybean cells was caused by III, whereas other surfactants or herbicides produced only slightly higher effluxes than the controls. Mixtures of oryzalin-I or -II were the only combinations that enhanced efflux in soybean cells above that of cells treated with the surfactant or herbicide alone. However, on cotton cells all surfactants and oryzalin caused considerable leakage but no synergistic effects. Sugars were the predominant compounds leaked from the treated and control cells. Disorganization of all cellular membranes was caused by III whereas I and II disrupted only the chloroplast grana-intergrana thylakoids, causing abnormal grana. Herbicidal damage to the cell ultrastructure was minimal. Cells treated with combinations of surfactants and herbicides produced only those ultrastructural symptoms that the individual chemicals caused when applied alone. Photosynthetic CO2 fixation was inhibited in both cotton and soybean cells treated with surfactants and (or) herbicides. Interference with membrane integrity, either directly by interaction with membranes or indirectly by interference with cellular energy generating systems that maintain membrane integrity is the postulated mode of action of these surfactants and herbicides.

Uptake, translocation, and metabolism of propham (isopropyl carbanilate) were ascertained for wheat (Triticum aestivum L., ‘Neepawa’) sugarbeet (Beta vulgaris L., ‘HH-10’), and alfalfa (Medicago sativa L., ‘Cherokee’) when grown in either liquid culture or in soil. Three-week-old wheat and 5-week-old sugarbeet and alfalfa plants were treated with 14C-propham in liquid culture for 1, 2, and 4 days. Other plants were placed in treated soil at 10 weeks after germination and grown for 15 weeks. Wheat absorbed 98%, sugarbeet 93%, and alfalfa 81% of the propham from solution after 4 days. Propham was translocated in all species. Under liquid culture, three polar metabolites of propham were isolated from wheat and alfalfa extracts and one was isolated from sugarbeet extracts. The agylcone moiety of the two most polar wheat metabolites was isopropyl-4-hydroxycarbanilate and that of the least polar metabolite was isopropyl-2-hydroxycarbanilate. The aglycone of all alfalfa and sugarbeet polar metabolites was isopropyl-4-hydroxycarbanilate. Only one polar metabolite was isolated from all soil-treated plants. The aglycone moiety was determined to be isopropyl-4-hydroxycarbanilate. Of the propham absorbed 95, 91, 89, and 36% was metabolized by sugarbeet roots, sugarbeet leaves, wheat leaves, and alfalfa leaves, respectively, after a 4-day liquid culture treatment. Propham was 100% metabolized when applied to plants via soil application.

Quackgrass [Agropyron repens (L.) Beauv.] was controlled by spring application of pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide] in 1970 and 1971, but when spring rainfall was below nornal in 1973, only pronamide applied the previous fall gave control. Terbacil (3-tert-butyl-5-chloro-6-methyluracil) gave 90% control of quackgrass for 2 yr at 2.2 kg/ha. Some control continued for 3 yr at 4.5 kg/ha. Three applications of glyphosate [N-(phosphonomethyl)glycine] at 3 kg/ha applied during a 2-yr period controlled quackgrass 97 to 100%. Phytotoxicity was not observed on 14-yr-old highbush blueberries (Vaccinium corymbosum L.) from pronamide or terbacil, on 4-yr-old blueberries from pronamide, or on 2-yr-old rhododendrons (Rhododendron × ‘A. Bedford’) from dichlobenil (2,6-dichlorobenzonitrile), pronamide, or directed sprays of glyphosate or amitrole (3-amino-s-triazole).

A weevil, (Rhinocyllus conicus Froelich) was introduced into Missouri in 1975 to aid in reducing populations of musk thistle, (Carduus nutans L.). The weevil was recovered in 1976 from as far as 3.2 km from the release site and 4.8 km in 1977. Infestation levels of flower heads at the release site ranged from 46 to 90%. Native parasites (Bracon mellitor Say) and [Aliolus curculionis (Fitch)] were reared from weevil larvae.

Nine substituted dinitronaline herbicides were studied to determine their effectiveness in controlling common root rot of peas (Pisum sativum L.) caused by Aphanomyces euteiches Drechs. under field conditions. Most of the dinitroaniline herbicide treatments increased plant stand, plant fresh weight, and shelled pea yield due to root rot suppression in each of the three years studied. Weed control was good in all plots and did not contribute to yield differences. Root rot suppression and crop injury were the primary determinants of yields. The greatest yield increases when compared with the weeded control were 82% for 0.56 kg/ha of dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) in 1974, 80% for 0.84 kg/ha of fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl) aniline] in 1975, and 26% for 1.68 kg/ha of pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] in 1976. The best average yield increases over all years were 54% for the combination of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) at 0.56 + 0.56 kg/ha, 49% for fluchloralin at 0.84 kg/ha, and 43% for pendimethalin at 0.84 kg/ha. Annual applications of 0.84 kg/ha of trifluralin delayed the rate of pathogen infestation of a field repeatedly planted to peas.

The adsorption of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] was measured on soil at water:soil ratio of 5:1 and 0.4:1. The adsorption isotherms for atrazine were described by the Freundlich equation. A decrease in water:soil ratio and in soil moisture content led to an increased adsorption of the herbicide. Increasing the concentration of electrolytes in the soil solution by adding solutions up to 0.1M CaCl2 increased atrazine adsorption. Greater amounts of atrazine were adsorbed at 30 than at 5 C on four soils at 0.1 bar moisture content. This indicates an endothermic reaction which was observed both before and after correction for differential atrazine solubility due to temperature. Thermodynamic quantities associated with the adsorption reaction were calculated to characterize the adsorption of atrazine on soil.

Yellow nutsedge (Cyperus esculentus L.) and purple nutsedge (C. rotundus L.) were grown in clay pots in the field to investigate the effect of sunlight intensity, planting date, and harvesting date on growth and development. Reducing the length of the growing season by delayed planting or early harvesting reduced the growth (dry matter accumulation) and tuber production of both species. Purple nutsedge growth (dry matter accumulation) was linearly reduced at 30 and 73% shade, but yellow nutsedge growth at 30% shade was not different from that at full sunlight. Tuber production in both species began about August 1, with slight delays in the initiation of tuber growth as planting date was delayed. At the end of the growing season a significant number of tubers were formed in both species even at the latest planting date under 73% shade.

Western ironweed (Vernonia baldwinii Torr.) and gray goldenrod (Solidago nemoralis Ait.) were mowed at various frequencies during two growing seasons in two experiments for each species. The initial mowings were made in late May or early June when rapid growth was taking place, presumably at the expense of carbohydrate reserves and also on June 15 and July 1. Subsequent mowings were made whenever the weed regrowth had reached 15 to 20 cm. The greatest reduction of western ironweed occurred with multiple mowing when the initial mowing was made on May 20. The degree of control was less in the second experiment than in the first. Multiple mowing was highly effective for reducing the stands of gray goldenrod; but in one of the two experiments, single mowings per season were almost as effective as multiple mowings.

A comparative scanning electron microscopy (SEM) study was performed on the surfaces of seeds and coleoptiles of several conspecific rice (Oryza sativa L.) varieties including the weed red rice and several cultivars: Mochi-Gommi and LA-110 (medium grained); Starbonnet, Labelle, and Bluebelle (long grained). Seed surfaces of red rice, LA-110 and Mochi-Gommi possessed trichomes that were more numerous at the seed apex than on other seed parts. Red rice also exhibited a large central awn extending from the seed apex. This awn had spines along its axis and numerous spines at its apical end. These characteristics were absent in the other varieties. No significant differences were noted in the seed-surface tubercles and in the quantity or structure of wax on the seed surface in all six samples. The coleoptiles of all samples had several similarities: the stomata were arranged in parallel rows on both the adaxial and abaxial surfaces, the epicuticular wax structure on both surfaces was rodlet, prickle hairs were found on the adaxial coleoptile surface (but absent on abaxial), spines were present on the edge of the apical end (older portion) and decreased in number toward the basal end (younger portion), and two types of papillae (based on size and shape) were present on both the adaxial and abaxial surfaces. Although there were varietal differences among developing coleoptiles on a macroscopic scale, significant morphological differences were not discernible at the SEM level.

The degree and longevity of quackgrass [Agropyron repens (L.) Beauv.] control provided by autumn applications of pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide] was influenced greatly by alfalfa (Medicago sativa L.) stand density, as well as by rate of application and soil type. When applications were made to a field with a sparse alfalfa stand (10 to 20 crowns/m2), quackgrass yields were reduced the year following pronamide application, but quackgrass reinfested the plots the second year after treatment. Quackgrass yields one and two seasons following autumn treatment with 2.2 kg/ha pronamide were 1480 and 3890 kg/ha compared to 4480 and 4870 kg/ha for control plots. Annual applications of pronamide were necessary to maintain quackgrass control in the sparse alfalfa stand. Pronamide application to a vigorous, dense alfalfa stand (40 to 50 crowns/m2) provided quackgrass control which persisted into the second year after treatment. Quackgrass control ratings one and two seasons after application of 1.1 kg/ha pronamide were 100 and 90%. Pronamide treatments reduced first cutting quackgrass yields, and increased first cutting alfalfa yields. Treatment of the sparse alfalfa stand with 2.2 kg/ha pronamide resulted in first cutting alfalfa and quackgrass yields of 2420 and 990 kg/ha compared to 1430 and 3940 kg/ha for controls. Treatment of a dense alfalfa stand with 1.1 kg/ha pronamide resulted in first cutting alfalfa and quackgrass yields of 3850 and 300 kg/ha compared to 1710 and 1660 kg/ha for controls. Total herbage yields from all cuttings were either slightly decreased when fields with sparse alfalfa stands were treated or remained constant or slightly increased when more dense alfalfa stands were treated. Pronamide applied with potash as the carrier was as effective as when applied in water. Pronamide treatment resulted in increased crude protein concentration in first cutting herbage at all locations in all years. Crude protein concentration in first cutting control herbage ranged from 13.3 to 16.1%. Crude protein concentration in first cutting herbage from plots treated with 1.1 kg/ha pronamide ranged from 17.7 to 20.6%, depending on year and location. In vitro digestible dry matter (IVDDM) concentrations were increased by most rates of pronamide in first, second, and third cutting herbage. IVDDM for first cutting control herbage was 51.4% compared to 61.3% for herbage treated with 2.2 kg/ha pronamide. Acid detergent fiber concentration in first cutting herbage was not affected by pronamide.

In field experiments during 1975 to 1977 the final yield of cucumbers (Cucumis sativus L. ‘Salty’) was unaffected when a naturally occurring weed infestation remained in the plots for the first 12 days after emergence in 1975 and for the first 24 days in 1976 and 1977, provided the crop was kept weed-free subsequently. If the cucumbers were kept weed-free for the first 12 days after emergence in 1975, 24 days after emergence in 1976, and 36 days after emergence in 1977, there was no loss of yield caused by weeds that emerged later in the season. The critical period of weed interference was therefore between 12 and 36 days after crop emergence. In other experiments, cucumber yields were reduced significantly when only 5% of the weeds were allowed to remain in the plots longer than 24 days after crop emergence. The percentage of various commercial grades, based on cucumber size, was not altered by weed interference and appeared to be dependent on harvesting frequency.