Cycloate (S-ethyl N-ethylthiocyclohexanecarbamate), applied by subsurface injection at 3.4 kg/ha, controlled 98 to 100% of barnyardgrass [Echinochloa crus-galli (L.) Beauv.] and 82 to 94% of common lambsquarters (Chenopodium album L.) and hairy nightshade (Solarium sarachoides Sendt.). Phenmedipham (methyl m-hydroxycarbanilate m-methylcarbanilate) at 1.1 kg/ha, applied after sugarbeets had emerged but before common lambsquarters had more than three pairs of true leaves or hairy nightshade had more than three or four true leaves, controlled the members of these species that had survived cycloate. Cycloate preconditioned sugarbeets and the surviving broadleaf weeds to injury be phenmedipham. Although applying phenmedipham following cycloate before sugarbeets had two pairs of true leaves sometimes resulted in severe crop injury, and applying it when weeds were too large resulted in incomplete weed control, in all experiments there was a period of at least 2 weeks during which application of phenmedipham killed the surviving lambsquarters and nightshade without injuring sugarbeets.

Diclofop-methyl {methyl ester of 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} applied as postemergence treatment at rates of 0.84 to 1.68 kg/ha controlled 65 to 87% of the wild oat (Avena fatua L.) without injuring flax (Linum usitatissimum L.) or rapeseed (Brassica campestris L. and B. napus L.) Yields of both crops were significantly increased because wild oat competition was minimized. Wild oat control was further improved when adjuvants were added with the herbicide at a concentration of 0.5% (v/v) to the spray mixture. Oil content, iodine number, and linolenic acid concentration of flax, and oil content of rapeseed were increased with the application of the herbicide, while the protein content of meal from both crops was unaffected. When flax was grown in the greenhouse under weed-free conditions, the 0.84 and 1.12 kg/ha rates of the herbicide did not affect seed and oil composition, whereas the 1.68 kg/ha rate decreased protein content, and slightly increased oil content, but had no significant effect on iodine number when compared with the untreated check. The change in seed and oil quality of flax appears to be related to a reduction in weed competition by the herbicide.

This study was conducted to evaluate the mobility of 14C-metolachlor over 1 yr for three seasons when applied preemergent to undisturbed field lysimeters with and without soybean representing cropped and noncropped zones, respectively. Leachate was collected weekly and analyzed for total 14C, metolachlor, and metabolites. Lysimeters were removed, sectioned, and analyzed for 14C. Sixty and 90 days after treatment (DAT), there was less soil water in lysimeters with soybean. Recovery of 14C in lysimeters decreased with time and ranged from 54 to 74% 30 DAT followed by a slower rate of loss with 35 to 49% remaining 365 DAT. Comparable amounts of total 14C were observed in soybean lysimeters as in fallow lysimeters 30, 60, and 90 DAT. 14C distribution in the lysimeters, however, was quite different. Sixty and 90 DAT, 14C mobility in soybean lysimeters was less than in fallow lysimeters. Also, less leachate was collected from soybean lysimeters, which resulted in later appearances and lesser amounts of 14C in the leachate. Cumulative leachate from lysimeters with and without soybean 365 DAT contained 2% and 10 to 18% of the applied 14C, respectively. Peak concentrations of 14C in leachate from fallow columns occurred about 90 DAT and were two to 19 times higher than 14C concentrations in leachate from soybean lysimeters. Metolachlor concentrations in leachate were well below the National Health Advisory level for drinking water in all cases. Apparent volatilization losses of 14C amounted to 26 to 46% of the applied 14C-metolachlor 30 DAT. These results suggest that herbicide mobility is different in cropped vs. fallow sites and possibly in intra- and interrow crop positions.

The application of 2,4-D [(2,4-dichlorophenoxy) acetic acid], at 1.1 kg/ha to common dandelion (Taraxacum officinale Weber) resulted in 40% or less survival in lawn and hayfield habitats, in both spring and fall treatments. A significantly lower incidence of regeneration (12 to 20%) was attained independent of the season by shoot removal (spudding) combined with 2,4-D in the lawn, but not in the hayfield habitat. No measure of control was obtained by spudding alone, confirming the high capacity of common dandelion for root regeneration. Removal of leaves 2 weeks after application of 2,4-D diminished the effectiveness of control in both lawn and hayfield habitats, with 49 to 50% and 60 to 70% regeneration, respectively. Apparently, there is incomplete translocation of the herbicide within this interval. Significant mortality from spudding alone was observed only in plants less than 4 months old (64% survival). One-year-old plants responded to all treatments in the same manner as common dandelion populations as a whole. Optimum control of common dandelion in lawns was obtained by 2,4-D application in combination with spudding, during the spring.

Investigations of smooth crabgrass growth and fenoxaprop-ethyl retention, foliar penetration, translocation, and metabolism were conducted at various soil moisture levels using a polyethylene glycol (PEG) semipermeable membrane system. The activity of fenoxapropethyl was significantly reduced at higher levels of moisture stress and this antagonistic effect was greater with increased duration of water deficit following herbicide application. Fenoxaprop-ethyl spray retention decreased linearly (23% total reduction) as soil matric potential (Ψm) decreased from −0.01 to −0.1 MPa. Foliar penetration and translocation of 14C-fenoxaprop-ethyl applied on the third true leaf were not affected by level or duration of moisture stress. Only 2% of the absorbed radioactivity was translocated out of the treated leaf for each moisture stress level and duration. As the soil Ψm decreased (−0.01 to −1.0 MPa) the relative levels of fenoxaprop-ethyl increased by 76 and 65% after a 48- and 96-h postapplication moisture stress period, respectively. In contrast, fenoxaprop acid decreased by 59 and 44% after 48 and 96 h of moisture stress, respectively. The relative level of fenoxaprop acid was linearly correlated to the antagonistic effect on shoot dry weight. These results suggest that decreased spray retention and, particularly, alterations in fenoxaprop-ethyl metabolism contribute to reduced fenoxaprop-ethyl activity observed in moisture-stressed smooth crabgrass.

Research during the past several decades on jointed goatgrass management has focused on individual cultural practices rather than on multi- or interdisciplinary components. Field studies were conducted at Hays, KS, from 1997 to 2003 to evaluate the interaction of crop rotation, fallow weed management, and winter wheat variety on jointed goatgrass density. Extending a wheat–fallow (W–F) rotation to include grain sorghum or grain sorghum and sunflower reduced jointed goatgrass populations more than other cultural practices tested. Fallow treatments were equal in most years, but mechanical fallow resulted in increased jointed goatgrass emergence compared with chemical fallow under drought conditions. Winter wheat cultivars had little effect on jointed goatgrass populations. However, taller, more competitive varieties are favorable for jointed goatgrass control in an integrated management program. No specific combination of crop rotation, fallow weed management, and wheat variety consistently reduced jointed goatgrass density more than other combinations during multiple years.

Seeds of fringed sage were collected in four different years in the Northern Mixed Prairie and placed in sealed vials in the field for up to 5 yr. The seeds were exhumed monthly and incubated at 10 or 20 C in light or darkness. Germination was greater at 10 than 20 C and greater in light than darkness. The overriding influences of light and temperature generally decreased as seeds aged. No well-defined dormancy/nondormancy or conditional dormancy/nondormancy cycles were revealed. Longevity of seeds varied among collections, ranging from 3½ to more than 5 yr. Patterns in germination of different collections were similar when they experienced the same annual changes in temperatures, indicating that germination of previously buried seeds of fringed sage was regulated by temperature. This regulating effect varied among years of storage; germination either increased or decreased with increasing temperatures, or was not affected. Results suggest that fringed sage seeds can germinate and emerge anytime during the growing season if temperature and moisture conditions are suitable. Continuous germination may enable fringed sage to occupy safe sites as they develop over time.

Soil lost through wind erosion may transport herbicides to nontarget areas. Shallow incorporation may reduce herbicide concentrations at the soil surface, thereby reducing loss on wind-erodible sediment (particles and aggregates less than 1 mm in diameter). Atrazine, alachlor, and acetochlor concentrations on and dissipation rates from surface wind-erodible sediment and larger size fractions from two soil types in undisturbed and incorporated (5 cm deep) treatments were compared. The surface 1 cm of soil was removed by vacuum 1, 7, and 21 d after herbicide treatment (DAT). This soil was dry-sieved into six size fractions (four fractions considered wind-erodible and two larger size fractions), and herbicide concentrations were determined on each size fraction. About 50% of the recovered material was classified as wind erodible sediment. Incorporation reduced herbicide concentrations on all size fractions and results were similar between soil types. Wind-erodible sediments from undisturbed and incorporated treatments contained about 65 and 8% of the applied herbicides, respectively, 1 DAT. Herbicide concentrations were similar among size fractions within a treatment 7 and 21 DAT; however, incorporation reduced soil herbicide concentrations from 50 to 80% compared to concentrations on soil from undisturbed areas. Shallow incorporation did not affect weed control ratings measured 30 DAT or herbicide dissipation. However, 50% dissipation rates (DT50) for each herbicide were about 15 d for wind-erodible sediments and ranged from 30 to 55 d for size fractions ≥1.68 mm.

Spray carrier pH affects the solubility of sulfonylurea herbicides and, therefore, could affect absorption and subsequent translocation of these compounds in weeds. Trifloxysulfuron is a sulfonylurea herbicide developed for POST weed control in cotton, sugarcane, and turfgrass with a pKa of 4.81. The objective of this study was to evaluate the absorption and translocation of foliar-applied 14C-trifloxysulfuron in Palmer amaranth and Texasweed at pH 5, 7, and 9 over a period of 4 to 72 h after treatment (HAT). For absorption, effects of time, species, and pH were significant. Absorption averaged over species and pH increased logarithmically from 4 to 72 HAT. Absorption was greater for Palmer amaranth (88%) than for Texasweed (29%) when averaged over time and pH. Absorption averaged over species and time increased in the order of pH 5 (52%) < pH 9 (60%) = pH 7 (61%). Consequently, this translated into greater translocation of 14C-trifloxysulfuron in Texasweed when sprayed with the higher pH spray solutions. These data indicate that absorption and translocation of trifloxysulfuron in some weed species may be enhanced by increasing the pH of the spray solution by 2 pH units above the pKa.

Requirements for germination and rate of juvenile root and shoot elongation of 23 medusahead (Taeniatherum asperum (Sim.) Nevski) selections were investigated in relation to osmotic stress. These were compared with the germination and elongation characteristics of other grasses. Aqueous solutions of different osmotic pressures were obtained by dissolving polyethylene glycol in water. Successive 4-bar increases in osmotic pressure markedly reduced medusahead germination until germination terminated at 16 bars. Other grass species exhibited higher germination than medusahead under osmotic stress. Medusahead juvenile root and shoot elongation under low and moderate osmotic pressure exceeded all other species tested.

This study was conducted to determine the effect of Canada thistle density and the direct and indirect effects of Canada thistle aboveground biomass and N concentration on wheat yield. A 4-yr experiment (1991–1995) with four Canada thistle densities (0, 4, 16, 64 plants m−2) was conducted. Initial statistical analysis showed a significant effect of Canada thistle density on wheat yield. Multiple regression and path analysis showed that the main factor causing wheat yield loss was Canada thistle N concentration. The second factor affecting wheat yield was Canada thistle biomass, and the last was Canada thistle density.

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine) affected oats and alfalfa in Nebraska planted the year following application to sorghum. No carry-over of 2-chloro-N,N-diallylacetamide (CDAA) + trichlorobenzyl (TCBC) was detected in oats and alfalfa. Intertillage of sorghum did not decrease herbicide residue.

Adoption of soybean that is resistant to 2,4-D will result in more use of glyphosate plus 2,4-D premixes and tank mixtures. Preliminary whole-plant greenhouse assays confirm most Palmer amaranth populations found in Indiana are glyphosate-resistant (GR), and some biotypes exhibit tolerance to 2,4-D amine. Dose–response experiments were conducted to determine the level of glyphosate resistance and 2,4-D amine tolerance in four Palmer amaranth biotypes. A premix formulation of glyphosate plus 2,4-D choline was also evaluated. The R1, R2, and R3 biotypes were 31- to 66-fold more resistant to glyphosate (R:S ratio) than the S1 biotype based on the herbicide dose to cause 90% mortality (LD90). The maximum POST rate of the premix formulation of Enlist Duo® labeled in ‘Enlist®’ soybean is 2,195 g ae ha−1. When separated by active ingredient, the maximum POST rate of Enlist Duo® is equivalent to 1,141 and 1,054 g ae ha−1 of glyphosate and 2,4-D choline, respectively. In the absence of glyphosate, the maximum rate of 2,4-D (1,054 g ae ha−1) in the premix formulation of Enlist Duo® controlled S1, R2, and R3 biotypes, but failed to control all plants from the R1 biotype. Estimates for LD90 showed the R1 biotype was 3-fold more tolerant than the S1 biotype to 2,4-D amine. However, no plants survived the 1,155 g ae ha−1 (600 g ae ha−1 of glyphosate plus 555 g ae ha−1 2,4-D) treatment with the premix formulation of glyphosate plus 2,4-D choline. Overall, results from this experiment suggest GR Palmer amaranth that also exhibits increased tolerance to 2,4-D amine will be difficult to control with glyphosate or 2,4-D alone, but can be controlled POST with Enlist Duo® at lower than labeled field rates (1,618 to 2,195 g ae ha−1).

Herbicide resistance has become a major topic of international research in weed science, with a steady stream of presentations and papers on various aspects of the biology of herbicide resistant weeds. Diverse sources—including WSSA—have generated an equally steady stream of recommendations for preventing and managing herbicide resistance. The situation in the field, however, continues to deteriorate, with new cases of herbicide resistant weeds being reported at an increasing rate. We know what to do, but why aren't we doing it?

Monuron [3–(p–chlorophenyl)–1,1–dimethylurea] is reported to be a potent inhibitor of the Hill reaction by Cooke and Wessels and van der Veen. It is reported to be 125 times as active as phenylurethan [ethyl–N–phenylcarbamate] in inhibiting the Hill reaction. Diuron [3–(3,4–dichlorophenyl)–1,1–dimethylurea] is 2500 times as active as phenylurethan as a Hill reaction inhibitor. Monuron and diuron have been used in photosynthetic studies. There are no reports in the literature indicating a difference in the mode of action of these compounds.

The effects of sublethal and lethal levels of 3-(3,4-dichlorophenyl)-l-methoxy-l-methylurea (linuron) on the uptake of 32P and 45Ca were tested on tomato (Lycopersicum esculentum Mill., var. Kokomo) and parsnip (Pastinaca sativa L., var. Harris Model). Both levels of foliage-applied linuron stimulated the uptake of 32P from nutrient culture solution and its translocation to the leaves. The increased 32P in the leaves of the treated tomato plants was found in the inorganic phosphate fraction. Incorporation of the label in the phospholipid and nucleic acid fractions was decreased slightly. Linuron inhibited uptake and translocation of 45Ca in both plants.

Broom snakeweed achene dispersal was monitored by placing surface-level traps outwards in the cardinal directions from 12 plants and collecting the achenes weekly or biweekly from September 1993 until seeds were no longer retained by the plants after 42 wk. About 50% of the achenes dispersed between October and December. Especially high numbers of achenes were dislodged during periods of intense winter winds and rains, with 78% of the seed placed into the east tray and 86% falling within 50 cm of the parent plant. Achene production averaged 3,928 (± 1,146) per plant in 1993 and 2,036 (± 987) per plant in 1994. Achenes collected over time directly from the inflorescence and achenes stored in nylon packets on the soil surface averaged 82% viability during fall and winter. Achene viability declined rapidly in late spring, and few remained viable before the next seed crop. Greenhouse experiments compared the influence of water application interval and water amount on broom snakeweed germination and seedling survival. Treatments consisted of 4 water intervals: daily, 5-d, 10-d, and 15-d intervals; and 4 water amounts: field capacity (1/1 fc), 3/4 fc, 1/2 fc, and 1/4 fc. Germination was 52% at daily 1/1 fc, and no seed germinated at daily 1/4 fc. Data suggest that optimum germination occurs when soils are maintained at a minimum soil matric potential (Ψm) > −180 kPa for at least 4 d. Optimum Ψm for seedling survival appears to range between −300 and −900 kPa, while seedling mortality would generally be expected with a Ψm of > −1800 kPa.

Chemicals that stimulate germination of curly dock seed (Rumex crispus L. # RUMCR) and urediniospores of curly dock rust [Uromyces rumicis Schum. (Wint.)], an obligate parasite of this weed, were studied and compared. Methyl salicylate, benzyl cyanide, and benzonitrile were the best stimulators of germination of curly dock seed. The compounds tested were most effective at concentrations ranging from 250 to 1000 μl/L. A 500 μl/L concentration of methyl salicylate caused 99% of the curly dock seed to germinate. Exposure to volatiles from 10 μl methyl salicylate or octyl cyanide for 16 to 24 h was required for maximum stimulation of curly dock seed germination in 10 days. Benzonitrile, methyl-2,4-dihydroxybenzoate, 3-cyanophenol, 2-heptanone, and benzaldehyde were the most effective of 45 compounds tested on urediniospores of curly dock rust. Benzonitrile was most active of 19 compounds tested on both seed and spores. Benzyl cyanide, 4-methoxybenzonitrile, benzaldehyde, and methyl 2,4-dihydroxybenzoate also were active on both propagules.

Horseweed is a winter annual weed that has evolved resistance to multiple herbicide modes of action in 11 countries worldwide. A paraquat-resistant horseweed population in an Ontario orchard that was being managed by a rotation of herbicides began to show increased tolerance to the herbicide linuron. Experiments were conducted in the greenhouse to compare the response of this population and several paraquat-susceptible populations to linuron, diquat, and oxyfluorfen. Plants were sprayed with a range of doses of each herbicide when they were from 5 to 10 wk old, and the ED50, or dose at which shoot dry weight was reduced by 50%, was estimated. There was a sevenfold difference in the ED50 values of the paraquat-resistant and -susceptible populations in response to diquat and a threefold difference in response to linuron. The response to oxyfluorfen was age dependent. The ratio of resistance to susceptible ED50 values was estimated as 57 for 5-wk-old plants and 11 for 8-wk-old plants in response to oxyfluorfen. Ten-week-old plants from both populations showed no response to oxyfluorfen at rates up to 4.8 kg ai ha−1.

In greenhouse studies, overhead watering or subsurface irrigating soil can cause fluctuating moisture content, as can treatments such as surface application of residue used in cover crop research. This paper introduces a method of capillary mat subirrigation that maintained soil moisture at about field capacity for 16 d while no moisture could be detected after 6 d in soil placed under similar conditions that was not irrigated. In another study, subirrigation eliminated differences in soil moisture due to the presence of surface-applied residue and moisture supplied by hand watering from overhead was apparently removed from subirrigated treatments, which never differed in soil moisture content.