This paper presents a framework in which the spatial and temporal domain of weed populations can be analyzed using geographically referenced information. The regional framework for analysis is based on the premise that the domain of a weed species or an assemblage of species can be described in terms of the space and time in which they survive. Published maps of the spatial distribution of individual weed species were converted to digital records defining their geographic domain. Digital records were imported into a geographically referenced data system. Assemblage maps were produced by intersecting domains of individual species. The assemblage maps show areas with similar intensity of the occurrence of species selected for analysis. The most intense occurrence of summer annual species, for example, exists in a relatively small area of the Midwest. The framework presented in this paper is a concept for a tool to evaluate, manage, and manipulate weed distribution data at the regional scale. Analysis at the regional scale is a perspective substantially different from the plot or field-scale analysis traditionally used to study and manage weed populations. Regional analysis has application to weed science by increasing the understanding of regional patterns of weed infestation and the factors that regulate them. This information will be useful to the herbicide industry, plant ecologists, resource managers, and agricultural policy makers.

Clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) was superior to 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], dicamba (3,6-dichloro-o-anisic acid), picloram (4-amino-3,5,6-trichloropicolinic acid), and triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} for control of honey mesquite (Prosopis glandulosa Torr. ♯ PRCJG) in the field. However, equal ratio mixtures of clopyralid + picloram or triclopyr (0.28 + 0.28 or 0.56 + 0.56 kg ae/ha) were as effective for honey mesquite control as clopyralid at rates of 0.56 and 1.12 kg/ha. Equal mixtures of picloram + 2,4,5-T, picloram + triclopyr, picloram + dicamba, triclopyr + 2,4,5-T, or triclopyr + dicamba were less effective in controlling honey mesquite than clopyralid alone or clopyralid + picloram or triclopyr in 1:1 mixtures. In the greenhouse, mixtures of clopyralid + 2,4,5-T, picloram, or triclopyr were highly effective for the control of honey mesquite. Mixtures of 2,4,5-T + picloram, 2,4,5-T + triclopyr, or triclopyr + picloram were also effective when applied at 0.28 + 0.28 kg/ha.

Economical combinations of herbicides and hand labor for weeding sugarbeets (Beta vulgaris L.) in high and low weed densities were determined for irrigated production in the southern Great Plains. Ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] preplant incorporated, a 50:50 mixture of phenmedipham (methyl m-hydroxycarbanilate m-methylcarbanilate) and desmedipham (ethyl m-hydroxycarbanilate carbanilate (ester)] sprayed postemergence on small weeds, and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) incorporated at layby controlled pigweed (Amaranthus spp.) and kochia [Kochia scoparia (L.) Schrad.] with acceptable selectivity in sugarbeets. Sucrose yield was identical for all methods of weed control. Using herbicides did not lower, and in some cases doubled, the total cost of weed control in an area with a low weed density. On the other hand, effective herbicide combinations saved $298 to $966/ha compared to total reliance on hand labor in an area with a high weed density. Elaborate combinations of herbicides were not justified even with heavy weed density. The last few weeds remaining in a field can be most economically removed by hand labor.

A survey was conducted in Mississippi from 1976 and in Arkansas and Louisiana from 1977 through 1991 to determine annual variation of johnsongrass infestation in cotton and soybean fields. The survey route was 1534 km long. Levels of johnsongrass infestation were estimated in 752 ± 296 cotton fields and 884 ± 407 soybean fields in each year of the survey. The area of fields surveyed annually was 47 000 ± 21 000 ha of cotton and 52 000 ± 19 000 ha of soybeans. Johnsongrass was present in 55 to 90% of the cotton fields. The percent of cotton fields with johnsongrass was about the same in 1991 as in 1976–77. About 90% of the soybean fields in Mississippi and Louisiana had johnsongrass, but only 70 to 80% of soybeans fields in Arkansas had johnsongrass. Soybean fields with 1 to 5% levels of infestation increased slightly in Mississippi but remained about the same in Arkansas and Louisiana. Soybean fields with infestations of 6% or more slightly decreased in Arkansas and Louisiana but not in Mississippi. It was estimated that johnsongrass reduces the average annual value of harvested cotton $5.8 ± 1.9 million and soybeans $23.7 ± 0.6 million in the three states.

Four synthetic multiring analogs of strigol (0.1 mM) were effective as germination stimulants of dormant, unchilled seeds of shepherdspurse (Capsella bursa-pastoris (L.) Medik. # CAPBP). The effect was concentration dependent and exceeded that produced by 0.1 mM gibberellic acid (GA). The analog treatments resulted in normal, unpigmented seedlings after 7 days, whereas GA treatment led to distorted, nongeotropic, yellow seedlings. The strigol analogs were also more effective in inducing shepherdspurse germination than 10 mM nitrate or 5.0 mM thiourea (ineffective in the dark) and 5.0 mM thiourea plus 4.5 mM ascorbate (germination stimulated, but seedling growth, inhibited). Chilling at 4 C for 11 days reduced the effectiveness of the strigol analogs, but not that of gibberellic acid and thiourea plus ascorbate. Ascorbate acts synergistically with thiourea in promoting shepherdspurse germination. Strigol and epistrigol had no effect on either chilled or unchilled shepherdspurse seeds. The stimulation of dormant shepherdspurse seeds by the synthetic strigol analogs is the first demonstration that these compounds have bioregulatory activity in dormant seeds of genera other than Striga.

Field experiments were conducted from 1985 to 1987 to evaluate herbicide systems for minimum-tillage and conventional-tillage peanut production. While acceptable weed control could be achieved in both tillage systems, minimum-tillage systems generally had to be more herbicide intensive. Preemergence or preplant-incorporated within-the-row applications of either ethalfluralin or pendimethalin plus postemergence applications of paraquat and sethoxydim provided Texas panicum control equivalent to preplant-incorporated applications of ethalfluralin or pendimethalin. Early-postemergence paraquat applications improved Florida beggarweed and pitted morningglory control in conventional-tillage systems at least 15% compared to the same systems without paraquat Control of bristly starbur and sicklepod in conventional-tillage systems did not increase with paraquat application. Broadleaf weed control did not differ between tillage systems, except pitted morningglory control was lower in the minimum-tillage system. Conventional-tillage peanuts produced yields 800 to 1900 kg/ha higher, depending on herbicide system, and also provided greater net returns than minimum-tillage peanuts. The greater yield and net returns in conventional- versus minimum-tillage systems were not attributed to weed control or disease problems.

Differences were shown to exist in photosynthetic rate, transpiration rate, and carbon dioxide leaf diffusive resistance between atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] susceptible (S) and resistant (R) plants of redroot pigweed (Amaranthus retroflexus L.). Chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea] and diruon [3-(3,4-dichlorophenyl)-1,1-dimethylurea] were the only herbicides tested that controlled both biotypes, but all of the herbicides except norea [3-(hexahydro-4,7-methanoindan-5-yl)-1,1-dimethylurea] controlled the S biotype. Although photosynthetic activity and transpiration were reduced in both biotypes by atrazine at 50 and 70 ppm, the decline was much greater in the S biotype than in the R biotype and persisted a longer time in the S biotype. Leaf CO2 diffusive resistances of the biotypes were increased by atrazine applications. Mesophyll resistance was increased to a greater extent than stomatal resistance suggesting that reduction of photosynthesis is due to a greater effect of atrazine on the mesophyll tissue than on the guard cells.

Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} in various formulations and placements was applied to honey mesquite (Prosopis glandulosa Torr. # PRCJG), huisache [Acacia farnesiana (L.) Willd. # ACAFA], live oak (Quercus virginiana Mill. # QUEVI), Macartney rose (Rosa bracteata J. C. Wendl. # ROSBC), and Texas whitebrush [Aloysia gratissima (Gillies & Hook.) Troncoso # ALYLY]. There was little difference in a species response to the various tebuthiuron formulations. Pellets (20%) at 2 g ai/tree base reduced the canopy 85% and killed 50% of the honey mesquite. At 1 g ai/plant, two briquettes at 0.5 g ai each or pellets (5.14 g, 20%) killed 37 and 80% of the huisache, respectively. Pellets were no more effective at 2 g than at 1 g ai on huisache. Basal treatments of 0.25, 0.5, 0.5, 1, and 2 g ai tebuthiuron/tree killed from 8 to 22, 48 to 62, 62 to 85, and 92% of the live oak, respectively. Pellets at 2 g ai placed at the base reduced the canopy 83% and killed 59% of the Macartney rose. On Texas whitebrush, 0.25, 0.5, 1, and 2 g ai tebuthiuron/tree killed from 68 to 85, 75 to 100, 90, and 100% of the plants, respectively. Tebuthiuron persisted mainly in the upper 30 cm of soil for at least 15 months.

Aseptic cultures of isolated corn (Zea mays L. ‘North Dakota KE47101′) shoots and roots and soybean [Glycine max (L.) Merr. ‘Hawkeye’] seedlings absorbed and metabolized atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] similarly to plants grown and treated in nutrient solution under non-sterile conditions. Atrazine injured susceptible soybean seedlings more rapidly than can be explained on the basis of starvation alone. It is postulated that the herbicidal activity of atrazine is partly due to toxic secondary factor(s) which may be of biochemical or photochemical origin. The effect of the toxic secondary factor(s) was reversed by added sucrose independent of light.

Single topical applications of monosodium methanearsonate (MSMA) affected cotton (Gossypium hirsutum L.) growth more than did similar disodium methanearsonate (DSMA) applications. There was usually no difference in yield among rates and dates with single applications of DSMA. Single applications of MSMA at later dates and higher rates reduced yields. Repeated topical applications of MSMA reduced yields and affected boll weight, lint percentage, number of seed per boll, and fiber fineness as compared with these properties of cotton treated once with MSMA. Response of cotton to MSMA was related to the number of applications and rate of herbicide. Repeated applications of DSMA affected cotton yield, lint percentage, and number of seed per boll less than did MSMA.

ED50 values (the dosage required to reduce the posttreatment gain in dry weight by 50%) for diclofop applied to green and yellow foxtail [Setaria viridis (L.) Beauv. ♯3 SETVI and S. lutescens (Weigel.) Hubb. ♯ SETLU] at the two- and four-leaf stages were calculated from linear regression equations derived by plotting the logarithm of the applied dosage against the relative growth reduction expressed as a probit value. At the two-leaf stage, green foxtail was more susceptible to the chemical than yellow foxtail but at the four-leaf stage there was no significant difference in response of the two species. At least part of the difference in sensitivity of the two species at the two-leaf stage could be accounted for by differences in spray retention, with green foxtail retaining 1.8 times (expressed as μL/cm2) or 3.5 times (expressed as μL/g dry weight) as much spray as yellow foxtail, despite the fact that yellow foxtail had a greater projected leaf area. At the four-leaf stage, the amount of spray retained by both species calculated on a per gram dry-weight basis was significantly less than at the two-leaf stage, accounting in part for the higher ED50 values obtained at the later growth stage. However, there appeared to be no direct relationship between the amount of spray retained and the comparative growth response of the two weeds at the later stage of application.

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.

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.

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.