The persistence and movement of sethoxydim residues were determined in the top 45 cm of an Estherville sandy loam (sl), Port Byron silt loam (sil), and Webster clay loam (cl) in the field. Analysis of sethoxydim residues simultaneously quantified parent and eight metabolites by conversion to a common volatile end product, 3-[2(ethylsulfonyl)propyl]-pentanedioic acid dimethyl ester, followed by analysis using gas chromatography (GC) and a flame photometric detector. Recovery of residues from soil spiked with 100 μg kg-1 was 86 ± 21%. Residues remaining in soil 21 days after treatment (DAT) in 1989 were 37, 51, and 29% of the applied sethoxydim in the sl, sil, and cl, respectively, while in 1990, 86, 52, and 24% remained in the sl, sil, and cl, respectively. Alachlor remaining 21 DAT in 1989 was 66, 52, and 65% of that applied in the sl, sil, and cl, respectively, while in 1990, it was 16, 13, and 100% in the sl, sil, and cl, respectively. Atrazine had the greatest % of applied chemical remaining 21 DAT in 1989: 100, 71, and 73% in the sl, sil, and cl, respectively. of the atrazine applied in 1990, atrazine remaining 21 DAT was 87% in the sl, 42% in the sil, and 100% in the cl. Over all soils and years, the amount of total sethoxydim residues remaining 137 DAT was the least of the three herbicides. In terms of leaching, sethoxydim residues showed least movement, with minimal detections below 0 to 15 cm. Although sethoxydim appears to be advantageous over alachlor and atrazine in terms of potential impact on ground water quality, additional information regarding composition of the detected residues is needed to better assess its environmental impact.

Control of tall larkspur on mountain rangelands would substantially reduce cattle poisoning. Several herbicides were evaluated for their control of tall larkspur in subalpine and aspen vegetation types. Glyphosate (2.2 kg ai ha−1) and picloram (2.2 kg ae ha−1) killed more than 88% of larkspur plants in both vegetation types. Clopyralid and triclopyr were ineffective at comparable rates. Metsulfuron (88 and 138 g ai ha−1) provided variable control. Glyphosate is nonselective and killed all perennial vegetation, except for Thurbers fescue and mountain brome in the aspen type. Picloram applied at 4.5 kg ha−1 suppressed grasses on the subalpine site, but allowed grasses to increase at lower rates. All herbicides reduced forb cover.

In field studies, wild oat control with AC 222,293 and difenzoquat was not reduced when each herbicide was applied in combination with thiameturon or DPX-L5300. Mixtures of barban with thiameturon gave wild oats control similar to barban applied alone, but mixtures of barban with DPX-L5300 sometimes gave less wild oats control than barban applied alone. Control was reduced when diclofop was applied in combination with thiameturon in 1985 but not in 1986. When antagonism occurred, addition of crop oil concentrate (COC) at 1.2 L/ha to the diclofop-thiameturon spray mixture overcame the antagonism. When diclofop was applied in combination with DPX-L5300, control was reduced and antagonism could not be overcome by increasing the diclofop rate or by adding COC to the spray mixture. In greenhouse studies the inert ingredients in the thiameturon and DPX-L5300 formulations did not antagonize diclofop activity on wild oats. TLC analysis of 14C-diclofop solutions with and without thiameturon or DPX-L5300 revealed neither degradation products of diclofop nor evidence of complexing between diclofop and thiameturon or diclofop and DPX-L5300. Diclofop antagonism by thiameturon or DPX-L5300 was not due to a chemical or physical interaction between the herbicides in the spray mixture.

The herbicide 2,4-D [(2,4-dichlorophenoxy)acetic acid] was applied as sublethal rates to sugarbeets (Beta vulgaris L. ‘Mono Hy D2’) in the field at different growth stages to determine its effect on growth and yield. The greatest reduction in top growth occurred when the highest rate of 2,4-D, 0.07 kg/ha, was applied to the oldest plants (12-leaf stage). All rates of 2,4-D reduced the components of sucrose yield (percentage sucrose, percentage purity, and root weight) to the extent that, together, the three components contributed to a significant reduction in recoverable sucrose. The yields of recoverable sucrose were reduced 6.8, 7.8, and 13.2% by the 0.017, 0.035, and 0.07 kg/ha rates, respectively.

Euphorbia esula is an exotic perennial weed that is estimated to infest 650,000 ha in North and South Dakota, Montana, and Wyoming. The estimated annual economic effect of E. esula infestations in the four-state area is about $130 million. We present the results of a survey of ranchers, local decision makers, and public land managers of grazing and nongrazing property from a five-county area in North and South Dakota, Montana, and Wyoming. A total of 565 ranchers, local decision makers, and public land managers were surveyed, which resulted in 267 completed questionnaires. The main objective of the survey was to evaluate respondent's perspectives of managerial, institutional, and social factors that may affect the rate and extent of implementation of various E. esula control strategies. The reasons for not using the various E. esula controls generally fell into environmental, financial, and educational categories. In many cases, little can be done to remove environmental constraints; however, financial constraints may be addressed through cost-share programs either offered locally or through state agencies. The other main reason for not using some controls was a lack of knowledge to work with various controls (e.g., grazing and biological controls). These obstacles could be addressed with workshops, demonstrations, or educational bulletins. These educational tools could be provided by universities or governmental agencies, as respondents indicated this was their choice for information dissemination. Disagreements among the survey groups were not substantial, and many share similar concerns in controlling the weed.

The uptake and translocation of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} were examined in sago pondweed (Potamogeton pectinatus L.) and Richardson pondweed [Potamogeton richardsonii (Ar. Benn.) Rydb.]. Root and shoot tissues of both species were isolated from each other with wax barriers and treated individually with 1.0 ppm 14C-fluridone. Both tissues bioconcentrated fluridone, but the amount absorbed represented 1% or less of the total herbicide available. Limited root-to-shoot translocation occurred, but shoot-to-root transport was negligible. In contrast to fluridone, highly mobile glyphosate [N-(phosphonomethyl) glycine] translocated from the shoots to the roots in sago pondweed. No metabolism of fluridone was detected in sago pondweed.

Salt rabbitbrush [Chrysothamnus nauseosus (Pallas) Britt., ssp. consimilis (Greene)] and greasewood [Sarcobatus vermiculatus (Hook.) Torr.] grow slowly in early spring until mid to late May. They then begin a period of rapid growth, at which time susceptibility to foliar herbicides is probably greatest. Greasewood ceases rapid growth in mid June to early July, but salt rabbitbrush continues to grow rapidly until early August. Greasewood that resprouts after herbicide application has a longer rapid-growth period than shrubs in an untreated stand. An average leader length of 4 cm indicates that rapid growth of salt rabbitbrush is underway, and first opening of the flower buds indicates that rapid growth is over. Appearance of greasewood staminate spikes indicates that rapid growth has begun, and the first appearance of dried spikes indicates that growth has ceased. Simultaneous control of these shrubs with a single application of phenoxy herbicides may only be possible during the relatively short period when both are growing rapidly. This period may only occur from late May to mid June in some stands and years, but may occur from mid May to early July in other cases.

A charcoal barrier was used to determine the importance of root, shoot, and seed exposure on the activity of nine acetanilide herbicides to peas (Pisum sativum L.) grown in a greenhouse. Greater reduction of plant weight occurred from root exposure than from shoot exposure. For all herbicides, the average reduction in shoot and root weight from shoot exposure was 7 and 20%, respectively; and root exposure reduced shoot and root weight 15 and 40%, respectively. The average reduction in shoot and root weight from exposing all plant parts to herbicides was 47 and 69%, respectively. Seed exposure had no influence on plant weight. This response indicates that pea roots are the primary site of activity for many acetanilide herbicides, and provides support to previous findings that showed rainfall was necessary to leach acetanilide herbicides down to the root zone of processing peas for maximum reduction of shelled pea yield. Field studies, conducted over a 2-yr period, were designed to evaluate annual weed control and pea injury from preemergence and early postemergence applications of seven acetanilide herbicides. Shelled pea yield was not reduced by any treatment. All treatments provided good to excellent grass control and fair to good broadleaf weed control.

Ultraviolet-B (UVB, 280 to 320 nm) radiation levels reaching the earth's surface are increasing because of depletion of the stratospheric ozone layer. Adverse biological effects of this harmful radiation are a serious concern. The effects of UVB radiation on spotted chickweed, dandelion, downy brome, green foxtail, redstem filaree, and common catsear seed germination, shoot and radicle elongation, and seedling growth and development in a UVB-free environment after exposure to UVB were investigated in a greenhouse study. UVB radiation (4, 7, or 11 kJ m−2 d−1) did not influence seed germination of any species except downy brome. Postgermination UVB exposure (8 h d−1, for 10 d), however, inhibited radicle elongation in all species, except in spotted catsear. Shoot elongation was also inhibited in some species but to a lesser extent than radicle elongation. A significant inhibition by UVB treatment (11 kJ m−2 d−1) of root and shoot biomass, leaf area, and leaf number was observed in some species after transfer of UVB-treated seedlings to a UVB-free environment for 3 wk. The inhibition of postgermination shoot and radicle elongation by UVB radiation, the continuation of growth inhibition after transfer of the treated seedlings to a UVB-free environment, and the differential responses of weedy species could have significant implications for their ability to compete with each other and with associated crops in a UVB-enriched environment that is likely as the stratospheric ozone layer gets depleted.

This 4-yr experiment was conducted to develop a profitable conservation tillage system for dryland and furrow-irrigated cotton in a winter wheat-fallow-cotton cropping system at Etter, TX. In the 2-yr cropping sequence, winter wheat was planted immediately after cotton harvest in mid-November and furrow irrigated. Three residual herbicide treatment combinations with atrazine or propazine with fluometuron, or propazine alone were sprayed on stubble after wheat harvest in late June and compared to repeated applications of glyphosate and conventional disk tillage. Glyphosate was used to control weeds that escaped residual herbicides. The following March, fluometuron, prometryn, and 2,4-D were sprayed on no-tillage treatments and trifluralin was incorporated with conventional planting. Hoeing cost ha-1 to control Palmer amaranth and kochia averaged about $13 where trifluralin was used, $38 when initial treatment included fluometuron, $63 with propazine, and $93 when glyphosate alone was used to control weeds in fallow. Lint yield on dryland was about 390 kg ha-1 with disking and when glyphosate was followed by disking in spring, and 540 kg ha-1 with no-tillage. With irrigation, lint yield was 660 kg ha-1 with disking and 759 kg ha-1 with the best no-tillage treatment. Long-term profits ha-1 on dryland ranged from $340 for disking to $524 for propazine no-tillage. With irrigation, profit ha-1 ranged from $707 for disking alone to $751 when glyphosate was used after wheat harvest and followed by disking and incorporation of trifluralin the next spring before planting cotton.

Wild oat control options are limited in western Canada due to resistance to most common herbicides. Control of wild oat with pyroxasulfone, a soil-applied, very-long-chain fatty-acid inhibitor, was investigated. A series of greenhouse and field experiments were conducted to isolate the effects of vertical seed position, site of herbicide interception, and tillage on wild oat control with pyroxasulfone in comparison with triallate. In greenhouse experiments, wild oat shoot length (soil surface to leaf tip) was reduced (P<0.05) in shallow-seeded wild oat compared with deep-seeded wild oat with pyroxasulfone (6.2 and 9.8 cm, respectively) and triallate (3.7 and 13.2 cm, respectively). Soil-applied pyroxasulfone remained in the top 2.5 cm of the soil with or without a simulated rainfall event. Pyroxasulfone was most effective if either the seed or the shoot 1 cm above the seed intercepted the herbicide layer. If a wild oat emerges from deeper in the soil profile, the sensitive part of the seedling may not intercept an effective rate of pyroxasulfone in the soil. In field experiments comparing deep- and shallow-seeded wild oat treated with pyroxasulfone and triallate in fields with and without tillage, there were no significant effects of tillage alone on wild oat shoot length. Deep-seeded wild oat emerged early, and while herbicides reduced shoot growth, shoots were >10 cm. Shallow-seeded wild oat had delayed emergence, possibly due to reduced soil moisture, and herbicides reduced shoot growth to <10cm. Pyroxasulfone is likely to be more effective in no-till fields where wild oat seeds are not located deep in the soil.

Wild mustard (Sinapis arvensis L.) is a widespread weed of the southeastern cropping region of Australia. Seed germination ecology of S. arvensis populations selected from different climatic regions may differ due to adaptative traits. Experiments were conducted to evaluate the effects of temperature, light, radiant heat, soil moisture, salt concentration, and burial depth on seed germination and seedling emergence of two populations (Queensland [Qld] population: tropical region; and Victoria [Vic] population: temperate region) of S. arvensis. Both populations germinated over a wide range of day/night (12-h/12-h) temperatures (15/5 to 35/25 C), and had the highest germination at 30/20 C. Under complete darkness, the Qld population (61%) had higher germination than the Vic population (21%); however, under the light/dark regime, both populations had similar germination (78% to 86%). At 100 C pretreatment for 5 min, the Qld population (44%) had higher germination than the Vic population (13%). Germination of both populations was nil when given pretreatment at 150 and 200 C. The Vic population was found tolerant to high osmotic and salt stress compared with the Qld population. At an osmotic potential of −0.4 MPa, germination of Qld and Vic populations was reduced by 85% and 42%, respectively, compared with their respective controls. At 40, 80, and 160 mM sodium chloride, germination was lower for the Qld population than the Vic population. Averaged over the populations, seedling emergence was highest (52%) from a burial depth of 1 cm and was nil from 8-cm depth. Differential germination behaviors of both populations to temperature, light, radiant heat, water stress, and salt stress suggest that populations of S. arvensis may have undergone differential adaptation. Knowledge gained from this study will assist in developing suitable control measures for this weed species to reduce the soil seedbank.

Weed management is a major challenge in organic crop production, and organic farms generally harbor larger weed populations and more diverse communities compared with conventional farms. However, little research has been conducted on the effects of different organic management practices on weed communities and crop yields. In 2014 and 2015, we measured weed community structure and soybean [Glycine max (L.) Merr.] yield in a long-term experiment that compared four organic cropping systems that differed in nutrient inputs, tillage, and weed management intensity: (1) high fertility (HF), (2) low fertility (LF), (3) enhanced weed management (EWM), and (4) reduced tillage (RT). In addition, we created weed-free subplots within each system to assess the impact of weeds on soybean yield. Weed density was greater in the LF and RT systems compared with the EWM system, but weed biomass did not differ among systems. Weed species richness was greater in the RT system compared with the EWM system, and weed community composition differed between RT and other systems. Our results show that differences in weed community structure were primarily related to differences in tillage intensity, rather than nutrient inputs. Soybean yield was lower in the EWM system compared with the HF and RT systems. When averaged across all four cropping systems and both years, soybean yield in weed-free subplots was 10% greater than soybean yield in the ambient weed subplots that received standard management practices for the systems in which they were located. Although weed competition limited soybean yield across all systems, the EWM system, which had the lowest weed density, also had the lowest soybean yield. Future research should aim to overcome such trade-offs between weed control and yield potential, while conserving weed species richness and the ecosystem services associated with increased weed diversity.

Tomato (Lycopersicon esculentum Mill.) plants possess a high degree of tolerance to postemergence applications of 3-chloro-2-methyl-p-valerotoluidide (solan). Eggplant (Solarium Melongena L.) is highly susceptible to this herbicide. Differences in penetration, persistence and metabolism of solan by tomato and eggplant were insufficient to account for the differential susceptibility. Solan greatly inhibited the Hill reaction in isolated chloroplasts, and chloroplasts of both species were about equally sensitive to it. Radioactive solan (carbonyl labelled) sprayed on intact tomato and eggplant accumulated to about the same extent in chloroplasts of both species. The Hill reaction in isolated chloroplasts, carbon dioxide (C14O2) fixation in intact plants, and the level of high energy phosphates in intact plants were determined for tomato and eggplant previously sprayed with a selective rate of solan. Initially, all three reactions were inhibited in both species. Later, all three reactions returned to normal in tomato, but declined to a low level in eggplant. A resistant mechanism of cyclic photosynthetic phosphorylation was proposed as the mechanism of solan tolerance in tomato. Two types of light-activated solan injury were found. A rapid non-selective action, occurring at high doses of the herbicide, killed both tomato and eggplant. A delayed action occurred selectively on eggplant at low rates of herbicide. No solan injury occurred on plants placed in darkness after spraying, regardless of plant species or rate of herbicide applied.

The absorption and translocation of labeled herbicides by submersed weeds was studied by sealing the immersed root system in a 60 ml polyethylene bottle and immersing the bottle and shoots in water in a 500 ml graduate. The medium for either roots or tops could be treated without affecting the other. Simazine [2-chloro-4,6-bis(ethylamino-1-C14)-s-triazine] and fenac [2, 3, 6-trichlorophenylacetic acid-1-C14 (mixed isomers)] were absorbed by both roots and shoots of waterstargrass (Heteranthera dubia) and translocated to the untreated portion (root or shoot) of the plant. The distribution patterns of C14-labeled simazine and fenac in bluegills (Lepomis macrohirus) were studied by gross autoradiography. The viscera of the fish contained the greatest amount of activity.

3-amino-2,5-dichlorobenzoic acid (amiben) and N-1-naphthylphthalamic acid (NPA) were applied to soybeans and 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) and 2-chloro-N, N-diallylacetamide (CDAA) to corn as sprays and as granules. Except where excellent weed control was established by the herbicides, rotary hoeing 2 weeks after application of the herbicides usually improved the degree of weed control without any detrimental effect on performance of the herbicides.

The pre-emergence use of herbicides offers a means of controlling weeds during the extremely critical period immediately following planting. Weeds can usually be controlled by cultivation if the crop makes a few weeks’ growth before weeds emerge. However, it is practically impossible to mechanically control weeds which emerge ahead of or with the crop.

Carrot (Daucus carota L. var. Imperator) seeds were planted in soil treated with amiben-C14 at 3 and 6 lb/A. Plants were harvested after 69, 103, and 191 days, autoradiographed or analyzed for the radioactivity in the 80 percent ethanol soluble fraction and in the insoluble fraction. The highest concentration of radioactivity was on or near the surface of the roots, but some radioactivity was present throughout the leaves and roots. The concentration of radioactivity decreased with time both in the soluble fraction and insoluble fraction of the root; in contrast it decreased in the insoluble fraction and increased in the soluble fraction of the leaves.

Disks of carrot root were placed in an aerated solution of amiben-C14. After 6 days, only 18.7 percent of the amiben remained unaltered. About 4 percent of the radioactivity was released as C14O2; 64.3 percent was present in an unknown compound which may contain a sugar moiety; the remaining 11.8 percent was distributed among four additional unknown compounds.

Quackgrass (Agropyron repens) is a weed of major importance in the northern regions of the United States where cool, humid climatic conditions prevail. In the areas of Wisconsin having a heavy red clay soil, the weed is especially troublesome for the soil characteristics hinder the most effective use of cultural control measures. The fact that quackgrass can be found on the majority of the farms in northern Wisconsin is evidence that effective methods of quackgrass control are not being used. The question arises of whether generally recommended methods of quackgrass control are effective under the conditions prevalent in this area. The present study describes the results obtained during 1947 and 1948 at the Ashland Branch Experiment Station using several combinations of tillage, cropping and fertilization. An attempt was also made to compare the value of two methods of estimating quackgrass infestations.

Two fish from South America. (Metynnis roosevelti Eigenmann and Mylossoma argenteum E. Ahl.), both called silver dollar fish, grazed rapidly on several species of submersed aquatic weeds. Horned pondweed (Zannichellia palustris L.), American pondweed (Potamogeton nodosus Poir.), and sago pondweed (Potamogeton pectinatus L.) were most palatable to the fish. Richardson pondweed (Potamogeton richardsonii (Ar. Benn.) Rydb.), curlyleaf pondweed (Potamogeton crispus L.), and American elodea (Elodea canadensis Michx.) also were grazed. The fish readily grazed on shoots of all sizes except those of mature plants. The Mylossoma grazed the plants more rapidly than the Metynnis. When water temperatures were above 70 F, the fish became more active in their feeding habits.