Effects of 22 herbicides on the ATP content of excised soybean [Glycine max (L.) Merr., var. Lee] hypocotyls were determined and compared with interferences reported previously on RNA and protein syntheses. Herbicides that reduced ATP levels and inhibited RNA and protein syntheses were 2-sec-butyl-4,6-dinitrophenol (dinoseb), 4-hydroxy-3,5-diiodobenzonitrile (ioxynil), 3′,4′-dichloropropionanilide (propanil), isopropyl m-chlorocarbanilate (chlorpropham), 2,3,5-trichloro-4-pyridinol (pyriclor), 2-chloro-N-isopropylacetanilide (propachlor), (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), and (2,3,6-trichlorophenyl)acetic acid (fenac). No herbicide was found which reduced tissue ATP levels, but did not inhibit RNA and protein syntheses. The correlations established between tissue ATP levels and inhibition of RNA and protein syntheses suggested that interference with the production of energy, required to drive the biosynthetic reactions, could be the mechanism through which these herbicides expressed their effects.

The dissipation and detoxification of 3,6-dichloro-o-anisic acid (dicamba), 4-amino-3,5,6-trichloropicolinic acid (picloram), and 2,3,6-trichlorobenzoic acid (2,3,6-TBA) was followed for 6 years at three locations across Nebraska. Herbicide persistence was determined by growing field bioassays of field beans (Phaseolus vulgaris L.) and soybeans [Glycine max (L.) Merr.]. Picloram showed the greatest soil persistence, 2,3,6-TBA was intermediate, and dicamba showed the least persistence across Nebraska. The residual phytotoxicity of picloram in soil was not necessarily dependent upon rainfall but was greatest in the fine textured soil with higher organic matter content.

Four 14C-labeled herbicide solutions were used to determine uptake and translocation patterns in mugwort (Artemisia vulgaris L.) roots. The 14C-(2,3,6-trichlorophenyl)acetic acid (14C-fenac) was bound in the roots and rhizomes and structures initiated on the rhizomes were heavily labeled. Little movement of 14C-isomers of fenac or 14C-fenac occurred from point of application on leaves. Rhizomes devoid of roots did not offer an appreciable avenue for entry of 2-chloro-4,6-bis-(ethylamino)-s-triazine (14C-simazine) into mugwort. Little movement of 3-amino-s-triazole (14C-amitrole) occurred from primary to secondary plants. Uptake of 14C-fenac was not increased appreciably by pretreatment of the plant root-rhizome system with (2,4-dichlorophenoxy)acetic acid (2,4-D), 2,4-dinitrophenol (DNP), or simazine.

About 25 ppm of 4-amino-3,5,6-trichloropicolinic acid (picloram) usually were detected on grass, primarily buffalograss (Buchloe dactyloides (Nutt.) Engelm.) and blue grama (Bouteloua gracilis Willd. ex HBK Lag ex Griffiths), immediately after application of 0.28 kg/ha picloram + 0.28 kg/ha (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) in northwest Texas. Less than 1 ppm of picloram usually was detected in grass tissue 30 to 60 days after treatment. At one location, detectable picloram increased in grass tissue from 32 to 60 days after application. Increases of picloram in aerial grass tissue were attributed to root uptake during a flush of vegetative growth. Picloram dissipation from grasses was not affected by irrigation to runoff at 10, 20, or 30 days after application. Detectable picloram was reduced by 93% in herbaceous, broadleaf species by 30 days after application. Treated sand shinnery oak (Quercus havardii Rydb.) leaves at the soil surface caused a slight increase of picloram in surface litter.

The activity of foliage applications of N,N-dimethyl-2,2-diphenylacetamide (diphenamid) was greatly enhanced by exposing the plants to high relative humidity for 6 hr immediately after chemical application. Growing plants under low light intensity further increased the activity of diphenamid under these conditions. This response occurred with a number of plant species, including tomato (Lycopersicon esculentum Mill.), Japanese millet (Echinochloa crusgalli (L.) Beauv., var. frumentacea), lettuce (Lactuca sativa L.), and radish (Raphanus sativus L.). Low light, but not high relative humidity, increased the activity of diphenamid as a soil application. Unaltered diphenamid and not its known metabolites seemed to be responsible for the increased activity of foliage sprays under conditions of low light and high relative humidity.

A 3-year field experiment was initiated in 1967 to study the effects of herbicides in combination with the systemic insecticide, O,O-diethyl S-2-[(ethylthio)ethyl] phosphorodithioate (disulfoton) on cotton (Gossypium hirsutum L.). Herbicide treatments of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), 1,1-dimethyl-3-(α,α,α,-trifluoro-m-tolyl)urea (fluometuron), 3-(hexahydro-4,7-methanoindan-5-yl)-1,1-dimethylurea (norea), 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin), and α,α,α,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) did not significantly affect yield of weed-free cotton while disulfoton treatment significantly increased yield over the 3-year period. Yield with disulfoton was negatively correlated with number of thrips (Thripidae sp.). No interaction occurred between herbicides and disulfoton on yield, and only in 1 year was there an effect on stand.

Winter wheat (Triticum aestivum L., var. Gaines) plots infested with seedling blue mustard (Chorispora tenella (Willd.) DC) were hand-weeded or treated in the fall with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) at 1 lb/A and 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil) at ⅜ lb/A. Additional wheat plots were established in the fall with populations of one, three, and nine blue mustard seedlings per square foot, and the next spring these were either untreated, hand-weeded, or treated with (2,4-dichlorophenoxy)acetic acid (2,4-D) at 1 lb/A. All plots were harvested in July. Maximum wheat yields were obtained from plots hand-weeded or treated in the fall. Wheat production decreased significantly as weed population increased. Grain yield reduction, resulting from weed competition during the winter months, was significant and accounted for more than 50% of the total loss.

Dimethyl tetrachloroterephthalate (DCPA) caused swelling of a localized region of the hypocotyls of cucumber (Cucumis sativus L., var. Wis. SMR-15), tomato (Lycopersicon esculentum Mill., var. Heinz 1370), and jimsonweed (Datura stramonium L.). DCPA caused stem swelling in jimsonweed by affecting dividing and/or differentiating cells in the vascular cambium. As swelling proceeded, xylem tissue was increased over the controls and xylem cells were disorganized and no longer continuous. Swelling was induced at the site of DCPA application, and was reduced when DCPA concentration per unit of stem was lowered, even though the same amount per plant was applied. Uptake of 14C-DCPA from the treated stem region was slow, but the treated area had the highest specific activity.

Several chemicals were evaluated for their potential use in selectively killing cocklebur (Xanthium pensylvanicum Wallr.) seed in cocklebur-cottonseed (Gossypium hirsutum L.) mixtures. Reduction in cocklebur embryo viability from 64 to 100%, without injury to cottonseed, resulted from soaking seed in: (a) 20% ethyl or methyl acetate and 80% water for 3 to 15 min; (b) 35% methanol, 15% glacial acetic acid, and 50% water for 3 to 15 min; or (c) 50% methanol or ethanol, 20% glacial acetic acid, and 30% water for 15 to 30 sec. Evaluations of injury were based on tetrazolium tests, standard germination, germination in soil, and seedling dry weight.

Added surfactant and high relative humidity enhanced penetration of 4-amino-3,5,6-trichloropicolinic acid (picloram) into leaves of Canada thistle (Cirsium arvense (L.) Scop.). Leaves and roots of Canada thistle readily absorbed picloram after which it was translocated in both phloem and xylem. Picloram tended to accumulate in young, growing leaves following both foliar and root uptake. In field-grown plants, injury symptoms appeared in young shoots as far as 1 m from treated shoots. The results are in harmony with a “source-to-sink” pattern of picloram translocation in the phloem. Leaves, but not roots, retained a substantial portion of the picloram absorbed. Following foliar application, small amounts of picloram were exuded by the roots into surrounding soil.

The techniques of cryostat sectioning, freeze-drying, and microradioautography were adapted to study the absorption and translocation of radio-labeled 3-(3,4-dichlorophenyl)-1,1-dimethylurea (14C-diuron) in root-treated cotton (Gossypium hirsutum L., var. Coker 201) plants. Diuron appeared to move primarily in the apoplast and to be transported acropetally and laterally in the transpiration stream. Radioactivity was observed to accumulate in striking concentrations in the lysigenous, or pigment, glands and the trichomes of the cotton plant. This accumulation is postulated to be a major factor in lowering the effective concentration of the herbicide in the leaves of cotton as compared to leaves of more susceptible plants, and thus may be a significant factor in the tolerance of cotton to diuron.

The technique of microradioautography was used to study the absorption and translocation of a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) by cotton (Gossypium hirsutum L., var. Coker 201) and soybean (Glycine max (L.) Merr., var. Lee). Radioactivity from 14C-trifluralin was retained primarily on the surfaces of the roots of cotton and soybean. This was apparently due to a tenacious adsorption or binding of the radioactivity to the epidermis and cuticle. Entrance of radioactivity into the roots of these species was greatly facilitated by breaks in the epidermis, such as might occur from seedling diseases or mechanical damage. Within the roots, radioactivity was noted in the walls of the xylem vessels and cortical cells. Little movement out of the soybean roots was observed, but limited movement of radioactivity into the leaves of cotton, apparently via the metaxylem, was noted. Radioactivity accumulated in the protoxylem of the cotton stem where many elements appeared to be plugged. Results of this study indicate that care should be used in interpreting data from studies where loss of radioactivity from nutrient media is used as a criterion of herbicide absorption, and where gross radio autography is used as an indicator of herbicide translocation.

Application of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) to intermediate wheatgrass (Agropyron intermedium (Host) Beauv.) increased forage yields, plant protein, and nitrate over a 4-year period. Atrazine or 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) applied to a sward of red brome (Bromus rubens L.), Arabian grass (Schismus arabicus Nees.), and red-stem filaree (Erodium cicutarium (L.) L'Her.) increased dry-matter yields sixfold and also increased protein and nitrate nitrogen. Nitrate in plants treated with atrazine increased to near-toxic levels for livestock.

Vernolate (S-propyl dipropylthiocarbamate) injected into a sandy loam soil controlled a higher percentage of early weeds in soybeans (Glycine max (L.) Merr.) in 2 years out of 3 when compared with incorporated vernolate at the same rate by conventional methods. Late season weed control was enhanced by split applications of herbicides applied postemergence in sequence with vernolate. Chloroxuron (3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea) applied early postemergence plus 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) or 2,4-bis-(isopropylamino)-6-(methylthio)-s-triazine (prometryne) applied in split applications as late and layby treatments gave the best weed control. Prometryne caused chlorotic veination in the upper leaves of the plants each year. In 1970, when prometryne was applied in sequence with incorporated vernolate, soybean plants were injured 30% compared with only 8% injury when the same herbicide was applied in sequence with injected vernolate at the same rate. The average seed yields were higher from injected vernolate at 1.12 kg/ha than from incorporated vernolate at 2.24 kg/ha. There was no difference in yield when vernolate was incorporated or injected at the same rate. Seed yields from the 3-year average were lower from plots treated with prometryne than from plots treated with linuron or 2-sec-butyl-4,6-dinitrophenol (dinoseb). Generally, the soybean seed quality was lower and seed size smaller when herbicide treatments failed to control weeds throughout the growing season.

Sunflowers (Helianthus annuus L.) produced maximum seed yields when kept weed free for a period of 4 to 6 weeks after planting. This was accomplished with one cultivation anytime between 2 and 6 weeks after the early planting in 1969, with two cultivations 2 and 4 weeks or 4 and 6 weeks after the late planting in 1969, and with one cultivation at 4 weeks after either the early or late planting in 1970. The average height of sunflower plants was not influenced by weed competition if weeded at either 2 or 4 weeks after planting, whereas, head and seed size were not affected if weeded at 4 weeks after planting. The oil content of seed was higher in plots with the least amount of weed competition.

Residues in soil, following application of 0.25 lb/A of 4-amino-3,5,6-trichloropicolinic acid (picloram) to semi-arid rangelands, usually were restricted to the top 12 inches for 60 days. Five ppb or less picloram were detected below 12 inches at 120 to 180 days after application; but picloram usually dissipated from the soil profile within a year. More picloram was detected 5 months after application at 6 to 18 inches deep at the lower ends of plots with 3% slopes than in plots with 0, 1, or 2% slopes. Runoff water from plots irrigated 10 days after treatment contained 17 ppb picloram. Irrigation or rainfall at 20, 30, or 45 days after picloram application resulted in less than 1 ppb picloram in runoff water. No more than 1 or 2 ppb picloram were detected after dilution of runoff water in large ponds.

The number of vascular bundles in the rhizomes of different ecotypes of johnsongrass (Sorghum halepense (L.) Pers.) varied from 71 to 154. The size of vascular bundles varied from 60 to 150 μ in an ecotype from California to 100 to 230 μ in an ecotype from Georgia. The size of xylem cells in these vascular bundles also varied widely, but the size of phloem cells was more constant. The number of vascular bundles in culms ranged from 43 to 123. The average number of vascular bundles in individual leaves varied from 46 to 158 for different ecotypes. The number of stomata on leaf surfaces deviated from 63 to 148/sq mm for 10 different ecotypes. An average of 95 stomata/sq mm occurred on the upper surface of johnsongrass leaves while an average of 113 stomata occurred on lower surfaces. The arrangement and size of stomata varied in different johnsongrass ecotypes.

Rates of 0, 1.7, and 3.4 kg/ha of 3-amino-2,5-dichlorobenzoic acid (chloramben) were incorporated to 0, 3.8, and 7.6-cm depths in 0.7 by 0.7-m microplots under low, moderate, and high rainfall conditions. Soybean [Glycine max (L.) Merr., var. Amsoy] injury increased with increasing depth of incorporation of 3.4 kg/ha chloramben. Chloramben incorporation under low rainfall conditions significantly improved control of giant foxtail (Setaria faberii Herrm.), smooth pigweed (Amaranthus hybridus L.), and velvetleaf (Abutilon theophrasti Medic.) compared to surface treatments. Jimsonweed (Datura stramonium L.) was not controlled well by chloramben regardless of rate or incorporation depth. In larger field plots over a 3-year period, 3.4 kg/ha chloramben incorporated with a disc produced slight but insignificant soybean injury. Giant foxtail, smooth pigweed, common ragweed (Ambrosia artemisiifolia L.), and velvetleaf control with incorporated chloramben was equal to or better than the control obtained with surface-applied chloramben. Regardless of method of application, control of common cocklebur (Xanthium pensylvanicum Wallr.), jimsonweed, and annual morningglory (Ipomoea spp.) was poor.

The growth of barley (Hordeum distichum L., var. Esperanza) seedlings in nutrient solution was reduced by purple nutsedge (Cyperus rotundus L.) plants growing in connected vials and by addition of ethanolic extract of purple nutsedge. Aqueous and ethanolic extracts from subterranean parts of purple nutsedge reduced the germination and root elongation of barley; stimulations of barley root elongation were obtained with diluted aqueous extract. The germination of barley, mustard (Brassica nigra L., var. Alsace), and cotton (Gossypium hirsutum L., var. Acala 1517) was reduced in soil which had been infested previously with purple nutsedge. Radicle elongation of barley was inhibited by ethanolic extract of soil previously infested. Chromatographic studies indicated that the inhibitors are phenolic substances.

Early postemergence applications of 2,6-dichlorobenzonitrile (dichlobenil) granules at 15 lb/A controlled 97 to 99% of dwarf waterlily (Nymphaea tetragona Georgi) in a shallow lake for 3 years. Dichlobenil alone was superior to a combination of dichlobenil and (2,4-dichlorophenoxy)acetic acid (2,4-D) for the control of dwarf waterlily and western yellow waterlily (Nuphar polysepalum Engelm). Reinfestation was more rapid on plots 25 by 25 ft in size than on plots 50 by 50 ft in size. When a high degree of control was maintained for 2 or 3 years, rhizomes of dwarf waterlily and a 1 to 2-ft layer of hydrosoil floated to the lake surface 17 months after dichlobenil was applied.