Enzymatically isolated American pondweed (Potamogeton nodosus Poir.) epidermal tissues were exposed to 14C-labeled dichlobenil (2,6-dichlorobenzonitrile), diquat (6,7-dihydrodipyrido[1,2-α: 2′, 1′-c] pyrazinediium ion), silvex [2-(2,4,5-trichlorophenoxy) propionic acid] or 2,4-D [(2,4-dichlorophenoxy)acetic acid] at concentrations of 5 × 10−4, 5 × 10−5, and 5 × 10−610M, and the amount of herbicide crossing the tissue layer was measured. Rates of herbicide movement were compared to those found when copper sulfate pentahydrate was added as a potential synergist at concentrations of 5 × 10−5 M (12.5 ppm), 5 × 10−6 M (1.25 ppm), and 5 × 10−7 M (0.125 ppm). Copper sulfate at 5 × 10−6 M increased the rate of movement of all herbicides. However, diquat and dichlobenil exhibited the most enhanced movement in the presence of copper sulfate. Without copper sulfate, 0.1 nmoles of 5 × 10−6 M 14C diquat penetrated the tissue within 24 h, compared to 1.3 nmoles following the addition of 5 × 10−7 M of copper sulfate.

Atrazine [2-chloro-4-(ethylamino)-6-isopropylamino)-s-triazine] carryover under reduced or no-till row crop production systems was measured by planting oats (Avena sativa L.) the following year as a field bioassay during 1970 through 1976 at Lincoln and North Platte, Nebraska. Oat yields indicate that soil persistence of normal-use rates of atrazine into the subsequent year is only a minor residue problem under reduced tillage cropping systems. Atrazine carryover in soil was less of a problem under these reduced tillage systems as compared with prior experiments with conventional tillage systems across Nebraska.

Of several herbicides tested on both monocotyledon and dicotyledon species, diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] was found to be the most effective in reducing transpiration in corn (Zea mays L.) plants; a reduction of 40% occurred. It was established that diuron was the active component in reducing transpiration, and not the additives in the commercial formulation (Karmex) used in this study. Foliar applications of low concentrations (0.035 to 0.56 kg/ha) of diuron effectively reduced transpiration in both cultivars (Pioneer 3780A and Pride 1108) of corn plants, at all stages of growth tested (from 3- to 10-leaf stage). This effect of diuron on reduced transpiration occurred when the supply of water or nutrients to the corn plants was either limiting or non-limiting. The reduction of transpiration of corn plants after treatment also prevented the leaves from wilting and becoming senescent. This effect was persistent over 16 days. Diuron treatment increased the water efficiency of the plants and this effect was more pronounced when water was limiting. Compared to the control, the treated plants used up to 68% less water for each gram of shoot dry weight produced. The increase in water efficiency indicates that transpiration was reduced more than photosynthesis.

Uptake and translocation of 14C-buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} in corn (Zea mays L.) and redroot pigweed (Amaranthus retroflexus L.) were studied following both foliar and root treatments under greenhouse and growth chamber environments. Following foliar application, 14C-buthidazole was absorbed by the leaves of corn and redroot pigweed seedlings in similar amounts. Translocation occurred only toward the tip of the treated leaves in corn, whereas in redroot pigweed the 14C moved both acropetally and basipetally. Rapid uptake by the roots and rapid movement to the leaves via the xylem seems to be the main pathway of uptake and translocation of 14C-buthidazole supplied to the roots of redroot pigweed plants. Uptake by both the roots and the emerging coleoptile and transport to the foliage seems to be the pattern of absorption and translocation of buthidazole in corn following preemergence application. Differences in absorption did not appear to be an important factor contributing to selectivity of buthidazole between corn and redroot pigweed. However, translocation of 14C-buthidazole supplied to the roots was faster to the redroot pigweed shoots than to corn shoots.

Soybeans [Glycine max (L.) Merr.] and oats (Avena sativa L.) were grown in a rotation using reduced or no-tillage crop production systems at Lincoln, Nebraska, over a 4-yr period. Oat stubble was treated after harvest with 3.4 kg/ha of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] to reduce the growth of late summer weeds. The following spring soybeans were planted directly into the undisturbed stubble or into a seedbed prepared by tandem discing. Three seedbed preparations, two soybean cultivars, and six preemergence weed control treatments were compared. Glyphosate [N-(phosphonomethyl)glycine] applied at 0.8 kg/ha or tandem discing were equally effective in producing a weed-free seedbed. Herbicides applied preemergence on soybeans were still necessary for the reduced tillage or no-tillage production systems if weeds were to be adequately controlled in soybeans without cultivation. Differences in seed-yield occurred between cultivars only when late summer rains benefited the later maturing ‘Williams' soybeans over earlier maturing ‘Wells'. With adequate weed control, soybeans and oats can be grown in a no-tillage, crop rotation, production system in eastern Nebraska to produce high yields with a minimum of labor and soil exposure.

Preliminary greenhouse studies indicated the presence of a synergistic interaction between low rates of fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] or diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] in combination with linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] or chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea]. In a 3-yr field study, moderate injury of cotton (Gossypium hirsutum L. ‘Stoneville 213’) with no yield reduction was observed with fluometuron or diuron at 1.68 and 1.12 kg/ha, respectively, but higher rates (5.04 and 3.36 kg/ha, respectively) caused injury and yield reductions. Soybean [Glycine max (L.) Merr. ‘Hill’] injury ratings during the second year indicated a synergistic interaction between residue from fluometuron at 5.04 kg/ha combined with linuron at 2.48 kg/ha or chlorbromuron at 3.85 kg/ha, and from diuron at 3.36 kg/ha combined with linuron at 2.48 kg/ha. These interactions were not apparent in soybean yield data. Soybean injury the third year ranged from 30 to 60% with single or repeated applications of linuron or chlorbromuron, although yields were not affected. Residual fluometuron and diuron from 2 yr of application at 5.04 and 3.36 kg/ha, respectively, injured soybeans, but did not reduce yields. Significant synergistic interactions were observed through injury and yield measurements after two annual applications of fluometuron at 5.04 kg/ha combined with linuron or chlorbromuron. A synergistic interaction was detected in soybean yields with chlorbromuron at 3.85 kg/ha preceded by two annual applications of diuron at 3.36 kg/ha. Such interactions may occur under field conditions, but are unlikely to be economically significant. Chemical analysis indicated little evidence of accumulation, even with repeated application of fluometuron or diuron at 5.04 and 3.36 kg/ha, respectively.

Ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] was evaluated in field experiments at rates from 0.6 to 4.5 kg/ha for control of volunteer wheat (Triticum aestivum L. ‘Hyslop’, ‘Stephens’) in fall-planted perennial ryegrass (Lolium perenne L. ‘Cropper’, ‘Pelo’, ‘Pennfine’, ‘Omega’). Ethofumesate applied at 1.7 kg/ha or more in mid-November to wheat in the one-to three-leaf stage eliminated the wheat. Wheat was not eliminated when ethofumesate was applied preemergence soon after planting or when applied at the end of November to wheat in the four-leaf to four-tiller stage. In four experiments in which wheat was present, ethofumesate significantly increased perennial ryegrass seed production. In one experiment in which wheat was not present, ethofumesate did not affect perennial ryegrass seed production. Ethofumesate applied in the fall at rates to 4.5 kg/ha to newly-seeded perennial ryegrass or to well-established bentgrass (Agrostis tenuis Sibth. ‘Highland’), Kentucky bluegrass (Poa pratensis L. ‘Newport’), and Italian ryegrass (Lolium multiflorum Lam.) did not adversely affect germination of the following seed crop.

Studies in outdoor, circular pools have shown that one shoot tip of hydrilla (Hydrilla verticillata Royle) produced as much plant dry weight during a 16-week period as 16 tips planted under the same conditions. Dry weight of plants 16 weeks after planting was as high as 1,561 times that of the shoot tips planted. Tubers were present within 8 weeks after planting the tips; higher numbers of these vegetative propagules were associated with the higher number of tips planted. Plants under a photoperiod of 11.5 h or less produced more tubers than those exposed to 12 h or more of light.

Soil-active herbicides were investigated for control of live oak (Quercus virginiana Mill.) on the Texas Coastal Prairie and Claypan areas with and without mechanical treatment. Roller chopping before, during, or after herbicide application had very little influence on mortality of live oak compared to the herbicide applied alone. Roller chopping did allow increased grazing of livestock for at least 3 yr after knockdown of the brush. Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} was generally the most effective herbicide for live oak control; bromacil (5-bromo-3-sec-butyl-6-methyluracil), karbutilate [tert-butylcarbamic acid ester with 3(m-hydroxyphenyl)-1,1-dimethylurea], and picloram (4-amino-3,5,6-trichloropicolinic acid) were somewhat less effective, especailly at 2.2 kg/ha. Limited data suggested that hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl]-1,3,5-triazine-2,4(1H,3H)-dione] also was highly effective for control of live oak. Primary invaders on either mechanically or chemically treated areas were American beautyberry (Callicarpa americana L.), southern dewberry (Rubus trivialis Michx.), boneset (Eupatorium perfoliatum L.), yankeeweed (Eupatorium compositifolium Walt.), brownseed paspalum (Paspalum plicatulum Michx.), and carpetgrass (Axonopus affinis Chase). A herbicide was generally equally effective for live oak control whether applied broadcast or in rows as granules, or applied as sprays to the soil surface or subsurface.

The response of tomato (Lycopersicon esculentum Mill. ‘Chico III’), jimsonweed (Datura stramonium L.), and velvetleaf (Abutilon theophrasti Medic.) to postemergence applications of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] applied after cloudy weather was determined by shading the plants artificially before field application of the herbicide. One day of 76% actual shade reduced the tolerance of tomato, jimsonweed, and velvetleaf to metribuzin, and 3 days of shade further reduced plant tolerance to the herbicide. The GR50 values showed that tomato was about 30 times more tolerant than jimsonweed and about 40 times more tolerant than velvetleaf to metribuzin. After 3 days of shade, 2 or 3 days of sunshine were required to return tomato to its full tolerance to metribuzin. After 3 days of cloudy weather, metribuzin applied at about 55% of the normal dose should control jimsonweed and velvetleaf. Weather conditions before postemergence applications of metribuzin will determine the appropriate timing of application and the herbicide dose.

Greenhouse-grown honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell] plants were treated with the propylene glycol butyl ether esters of 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], the triethylamine salt or the ethylene glycol butyl ether esters of triclopyr {[(3,5,6-trichloro-2-pyridinyl) oxy]acetic acicd}, the potassium salt of picloram (4-amino-3,5,6-trichloropicolinic acid), or the monoethanol amine salt of 3,6-dichloropicolinic acid applied at the rate of 1.1 kg/ha to soil, foliage, or soil plus foliage. All herbicides were effective as foliar sprays in killing the stems of honey mesquite. When applied to the soil, picloram and 3,6-dichloropicolinic acid killed all above ground stems, and the ester and amine formulation of triclopyr killed 70 and 91% of the stem tissue, respectively, but 2,4,5-T was ineffective. Accumulation of herbicides in leaves 10 days after foliar spray was 28, 167, and 266 μg/g fresh wt for triclopyr, 3,6-dichloropicolinic acid, and picloram, respectively. Upward transport of picloram and 3,6-dichloropicolinic acid (2.7 to 5.9 μg/g) was also more extensive than that of 2,4,5-T or triclopyr after soil treatment. Higher concentrations of 3,6-dichloropicolinic acid than 2,4,5-T, triclopyr, or picloram usually was found in honey mesquite stems and roots 3, 10, or 30 days after application to soil or foliage. This may be one reason that 3,6-dichloropicolinic acid is highly effective in controlling honey mesquite.

Root growth of three zoysia (Zoysia spp. ‘Emerald’, ‘Meyer’, and ‘Matrella’) cultivars and four bermudagrasses [Cynodon dactylon (L.) Pers. ‘Tifway’, ‘Tifgreen’, ‘Tifdwarf’, and ‘Ormond’] was determined after several consecutive annual herbicide treatments. Napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] reduced the root growth of all zoysia and bermudagrass cultivars. Prosulfalin {N-[[4-(dipropylamino)-3,5-dinitrophenyl] sulfonyl]-S,S-dimethylsulfilimine} retarded root growth of Tifgreen and Tifdwarf bermudagrass when treated at any rate. Tifway and Ormond bermudagrass and zoysia cultivars were retarded at the 3X rate (10.2 kg/ha). Zoysia grass roots were not affected by oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one], bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide], or benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) treatments. DCPA (dimethyl tetrachloroterephthalate) and oxadiazon did not reduce root growth of bermudagrasses, except when Tifgreen was treated with oxadiazon at 3X rate (13.4 kg/ha).

Field experiments were conducted to determine optimum nozzle settings for applying glyphosate [N-(phosphonomethyl)glycine] in the recirculating sprayer for postemergence control of johnsongrass [Sorghum halepense (L.) Pers.] in soybeans [Glycine max (L.) Merr.]. Herbicide sprays were directed across the row to johnsongrass growing taller than soybeans in July and August. Herbicide not sprayed on johnsongrass was trapped and reused. Glyphosate at 0.56, 1.12, and 2.24 kg/ha applied with commercially available 25° spray nozzles provided johnsongrass control and soybean yields equal to those following applications with specialized uniform droplet nozzles. Glyphosate at 1.7 kg/ha applied in the recirculating sprayer using only one nozzle per row provided control of johnsongrass equal to or better than that from applications made with two, three, or four nozzles per row. Soybean yield following application of glyphosate at 1.7 kg/ha with one nozzle per row was equal to yields obtained following its application with two, three, or four nozzles per row, with or without surfactant at 0.1% in spray solutions. Soybean yield was higher with four nozzles per row than with one nozzle per row when 0.5% surfactant was included in spray solutions. Soybean injury was lower and yield was higher when glyphosate was applied in the recirculating sprayer rather than over-the-top with a conventional sprayer. Glyphosate at 1.12 kg/ha applied in the recirculating sprayer caused more injury to ‘Hill’ and ‘Bragg’ than to ‘Forrest’ or ‘Tracy’ soybeans.

Two yr of field research were conducted to evaluate the efficacy of BAS-9021 {2-[1-(N-allyloxyamino)butylidene]-5,5-dimethyl-4-methoxycarbonylcyclohexane-1,3-dione, Na salt}, HOE 29152 {methyl 2-[4-(4-trifluoromethylphenoxy)phenoxy]propanoate}, and mefluidide N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide as selective herbicides applied postemergence to johnsongrass [Sorghum halepense (L.) Pers.]. All three herbicides afforded 85% or greater control of rhizome johnsongrass in one experiment in 1977, where repeat applications were made and ideal growing conditions prevailed. HOE 29152 also afforded excellent control with a single application made at the boot stage of johnsongrass. In a second experiment in 1977, when drought conditions prevailed, HOE 29152 was the only herbicide that afforded 70% or greater control of the johnsongrass. Both BAS-9021 and mefluidide afforded less than 60% control of johnsongrass in the single 1978 experiment, when evaluated at the end of the season. This study also was subject to drought conditions throughout the growing season.

In field studies conducted in 1971 through 1977 weed yields were higher in EPTC (S-ethyl dipropylthiocarbamate) and alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide]-treated areas as compared to handweeded plots. Weeds present in EPTC-and alachlortreated areas did not result in a significant field bean (Phaseolus vulgaris L. ‘Great Northern 59’) yield reduction as compared to hand-weeded plots. For every 1000 kg of dry weeds present in field beans there was a corresponding decrease in field bean yields of 208 kg/ha. Weed yields produced in plots treated with alachlor, dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), EPTC, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), and profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine] were significantly less when herbicides were incorporated with the rotary tiller as compared to incorporation with the spike-tooth harrow. Incorporation method was not as critical with butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine], with spike-tooth harrow incorporation of herbicides providing similar weed control to that obtained with the rotary tiller. Weed densities and yields were higher in plots seeded with field bean determinate variety ‘Great Northern 1140’ than in plots seeded with indeterminate variety ‘Tara’, when either EPTC or alachlor were applied preplant and incorporated. Neither field bean variety competed well with weeds when no herbicide was used.

When discs of red beet (Beta vulgaris L.) root were immersed in various concentrations of glyphosate [N-(phosphonomethyl)glycine] either in phosphate (pH 6.8) or citrate (pH 6.2) buffer, no efflux of betacyanin occurred even after 1 week. This suggests that glyphosate had little or no effect on membrane permeability. When beet discs were immersed in distilled water containing glyphosate, the betacyanin efflux increased with time and concentration. Measurement of pH indicated that the solutions were strongly acidic at first, but tended to approach a pH of 6.0 over 8 h, after which time betacyanin efflux slowed down or stopped. The tissue was able to buffer the solutions sufficiently to prevent further efflux. When tissue discs were immersed in a series of citrate buffer ranging from pH 3 to 6.2, efflux occurred at pH 3 and slightly at pH 6.2. Efflux was not altered significantly with the addition of glyphosate.

Moist-chilled and freshly harvested seeds of redroot pigweed (Amaranthus retroflexus L.) and yellow foxtail [Setaria glauca (L.) Beauv.] were tested for germination responses to soil ammonium and nitrate. A controlled environment was used to simulate overwintering and germination conditions in the field. The results suggest that no alteration of weed germination behavior should be expected in the crop ecosystems studied if ammonium plus nitrification inhibitor replaces other fertilizer systems which result in substantial levels of nitrate in the soil solution. The only germination effect was one of nitrate on unchilled foxtail. Chilling lowered catalase activity in both species.

Pronamide [3,5-dichloro-(N-1, 1-dimethyl-2-propynyl) benzamide] phytotoxicity was compared in 10 Wisconsin soils and the relationship of activity to soil physical and chemical properties appraised. Twelve soil properties were measured and correlated with pronamide I50 (50% fresh weight inhibition) values using oats (Avena sativa L. ‘Portal’) as the indicator plant in bioassays conducted under greenhouse conditions. Organic matter was the soil variable most inversely correlated with pronamide phytotoxicity. Cation exchange capacity, field moisture capacity, and Mg content were also inversely correlated with pronamide phytotoxicity, but probably reflect changes in soil organic matter levels. Clay content did not significantly affect pronamide phytotoxicity.

Caryopses (seeds) of fall panicum (Panicum dichotomiflorum Michx.) have a dormancy that is not easily overcome. Although accelerated after-ripening for 4 weeks was partially successful in overcoming dormancy, a dark imbibition at 35 C for about a week was more effective and also interacted strongly with an accelerated after-ripening. In either case, activation of phytochrome by red irradiation was required to induce germination. Similarly, alternating temperatures allowed germination of red-treated seeds but constant temperatures did not. More seeds germinated in sealed flasks than in dishes. The enhancement of germination in sealed flasks appeared to be related to increased CO2 levels. The data suggested a multiple dormancy in fall panicum seeds. One dormancy, the most intense, was relieved by high-temperature imbibition. The residual dormancy was relieved by active phytochrome and alternating temperatures.

Purposefully introduced plants that have become weeds cost the United States millions of dollars annually by reducing yields of crops and livestock, clogging navigable and recreational waterways, reducing productivity and value of grazing lands, poisoning humans and livestock, and increasing weed control costs. Research is in progress to develop methods of intercepting foreign plants that might be toxic to livestock if introduced on western ranges and pastures. Methods of intercepting include identifying poisonous plants from seed inventories, chemical analysis, chemotaxonomic investigations of biochemical relationships between related taxa, and feeding suspected plants to laboratory and domestic animals.