The environmental effect of weed control systems has stimulated research into new practices for weed control, such as selective herbicide application methods on weed-infested crop areas. This research used the color co-occurrence method (CCM) texture analysis to determine the effects of plant maturity on the accuracy of weed species classification of digitized images. Two different experimental combinations of weed species and maturity level were examined. The weed species evaluated were ivyleaf morningglory, giant foxtail, large crabgrass, and velvetleaf, with soil image sets added to each experiment. One study examined classification accuracies for two weed species at three maturity levels, and the second study examined four weed species at two maturity levels. For each species-maturity level combination, 40 digital images were collected from a manually seeded outdoor plant bed. Digitized images were transformed from the red–green–blue (RGB) color format into hue–saturation–intensity (HSI) format to generate CCM texture feature data. Stepwise variable reduction procedures were used to select texture variables with the greatest discriminant capacity. Then discriminant analysis was used to determine the classification accuracy for the two different experiments. When using HSI texture statistics, discriminant analysis correctly classified weed species within and across maturity levels with an accuracy above 97% for both experimental groups. These image processing algorithms demonstrate potential use for weed scouting, weed infestation mapping, and weed control applications using site-specific farming technology.

Neither glyphosate [N-(phosphonomethyl)glycine] nor the soil metabolite aminomethylphosphonic acid were detected in the first flow of water through two canals following application of glyphosate at 5.6 kg/ha to ditchbanks when the canals were dry. Soil samples collected the day before canals were filled (about 23 weeks after treatment) contained about 0.35 ppm glyphosate and 0.78 ppm aminomethylphosphonic acid in the 0 to 10-cm layer. When glyphosate was metered into the water at a rate calculated to provide 150 ppb in the canal water at a single site on two flowing canals, about 70% of the glyphosate was accounted for 1.6 km downstream from the application site. Thereafter, the rate of disappearance diminished, and about 58% of the applied glyphosate was present at the end of the canals 8 or 14.4 km downstream from the introduction sites.

The persistence of hormone-type herbicides in tissues of susceptible crop plants was studied under growth-chamber and field conditions. The susceptible plants selected were tomatoes (Lycopersicon esculentum Mill.), soybeans [Glycine max (L.) Merr.], and turnips (Brassica rapa L.). Foliage of each species was exposed to herbicides at levels that represented spray drift situations, and the decline of residues was investigated through subsequent chemical analysis. The disappearance of 2,4-D [(2,4-dichlorophenoxy)-acetic acid], 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid], mecoprop {2-[(4-chloro-o-tolyl)oxy]propionic acid}, 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and dicamba (3,6-dichloro-o-anisic acid) was almost linear when concentration data were plotted against the logarithm of time. The results indicate that for practical purposes a kinetic rate equation [conc. = a – b log (time)] would describe the residue decline.

Amine formulations of 2,4-D [(2,4-dichlorophenoxy) acetic acid] and MCPA {[(4-chloro-o-tolyl)oxy] acetic acid} caused a reduction in paraquat (1,1-dimethyl-4,4′-bipyridinium ion) phytotoxicity to barley (Hordeum vulgare L. 'Summit′), wheat (Triticum aestivum L. ‘Neepawa′), and wild oats (Avena fatua L.). Dicamba (3,6-dichloro-o-anisic acid) reduced paraquat activity in barley only. Paraquat phytotoxicity was antagonized more by 2,4-D amine at high than at low rates. Higher rates of paraquat relative to a fixed rate of 2,4-D amine overcame the antagonism. Paraquat phytotoxicity was not antagonized by 2,4-D or MCPA amine applied as a separate treatment. The technical components of the 2,4-D- or MCPA-amine formulations were solely responsible for the antagonism. Ester formulations did not affect paraquat phytotoxicity.

Photographic techniques and the point-frame transect method were used to study areal growth of kikuyugrass grown in the field without competition in 1990 and 1991. The effect of cutting height on plant extension was also examined in 1991. There were no differences in sward area between eight selections planted in 1990, except on the first measurement date, but selections differed in height and number of primary and secondary stolons. Expansion was irregular in all but one selection, and the patch shape of all irregular selections was defined by the direction and number of the earliest buds to sprout from the stolons. Only two of the eight selections were planted in 1991. Cutting height affected extension from the plot center, linear plant frequency, and plant biomass. The lowest height of cut, 2.5 cm, had the least extension and frequency, the higher cut, 5 cm, was intermediate, and the unmowed plots had the highest extension and frequency. There were differences between selections in number of nodes per unit area, which resulted in differences in response to mowing. Results from a greenhouse clipping experiment showed that although root weight of stolon sections used as propagules was reduced by defoliation, starch content was not affected. The spreading ability of kikuyugrass appears to be based on its ability to branch from its stolons presumably due to reallocation of resources. Based on these results, close mowing could slow the process of kikuyugrass invasion into other turf species but is inadequate to control it.

The most effective and dependable method of controlling wild cane [Sorghum bicolor (L.) Moench] in corn (Zea mays L.) was with a combination of cultivation plus herbicides. Timely cultivations were equally or more effective than preplant herbicides in controlling wild cane, but neither method was adequate by itself. The best herbicide in this study for the control of wild cane in corn was S-ethyl dipropylthiocarbamate (EPTC) alone or in combination with (2,4-dichlorophenoxy)acetic acid (2,4-D) or 2-chloro-4,6-bis-(ethylamino)-s-triazine (simazine). Residual effects of simazine at 4 lb/A in the soil reduced the yield of the following oats (Avena sativa L.) crop 1 out of 3 years.

Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)-acetanilide] mixed with plaster-of-paris in concentrations of 0.5, 1, 2, and 4% (w/w) was cast into tablets of three sizes. The controlled release of the herbicide was tested by the following methods: (a) in the laboratory with eduction by soaking tablets in water, (b) in the greenhouse with azalea (Rhododendron obtuseum Planch. ‘Richardii’) stock in container, and (c) in the lathe house with azalea stock in containers. In the laboratory experiment, the quantity of herbicide educed from tablets of equivalent volumes, weights, and concentrations were similar regardless of surface area of the three tablet sizes. Successively decreasing quantitites of alachlor were educed with each of the first 10 soakings. Following these soakings, the quantity of alachlor educed per soaking stabilized for the next 30 soakings. In both greenhouse and lathe house experiments, azalea plants treated with as much as 45 kg/ha alachlor formulated in tablet(s) were not damaged. In the best greenhouse treatments, two small tablets per container, effective weed control was obtained for up to 7.5 months from a single application of alachlor at rates of 11, 22, and 45 kg/ha.

Alien weed species rank among the most important threats to conservation of biodiversity, making understanding the extent to which protected natural areas are vulnerable to invasion by weeds pivotal in long-term maintenance and conservation of biodiversity. We investigated the potential geographic range of the invasive paleotropical weed, smooth crotalaria, in protected natural areas across Brazil. The ecological niche dimensions of smooth crotalaria in Africa (its putative original distribution) were modeled using a genetic algorithm. Models for the native range and their projections to South America showed good predictive ability when challenged with independent occurrence data. All Brazilian protected natural areas were predicted as highly vulnerable to invasion by this species. However, smooth crotalaria appears more likely to occur in open (savanna-like vegetation, such as cerrado and pantanal) and highly fragmented (Atlantic forest) areas than in extensive closed forests (Amazon). Management suggestions and research priorities are outlined based on these results.

In order to clarify the translocation and metabolism of glyphosate in lead tree, a mixture of glyphosate (0.5 mmol) and 14C-glyphosate was injected into mini tree plants (1.5-cm trunk diameter and 120 cm tall), simulating a grown lead tree in a greenhouse experiment. Within 6 d after treatment (DAT), all leaves on the lead tree plants dropped. Analysis of nonlabeled glyphosate in both xylem and phloem every 15 d showed that glyphosate residues accumulated mainly in phloem, similar to the findings in established lead tree. In this experiment, glyphosate concentration in the phloem of three parts of the trunk, i.e., upper (15 cm above the upper injection hole), middle (between the two injection holes), and lower (15 cm below the lower injection hole) parts, increased rapidly within 45 DAT, and decreased thereafter. Obviously, significant glyphosate metabolism occurred during the latter period. Further 14C radioactivity measurement also exhibited similar time-course changes of glyphosate dissipation, except that a low level of radioactivity in the phloem of the upper part and a high level of radioactivity in the lower part were detected from 45 to 90 DAT, suggesting that more glyphosate metabolites in the phloem of the upper part might have translocated with photosynthetic assimilates and reallocated to the lower part of the mini tree. Thin-layer chromatography (TLC) analysis of metabolites derived from 14C-glyphosate also revealed that about 70% of the radioactivity recovered in the phloem of the lower part comprised the unknown metabolites M1 (retention factor [Rf] : 0.83) and M2 (Rf : 0.94), with nearly 28% of the radioactivity from sarcosine (Rf : 0.76), and less than 2% of the radioactivity from aminomethylphosphoric acid (AMPA) (Rf : 0.49) and glyphosate (Rf : 0.36). It is concluded that active metabolism of glyphosate in this 90-d simulation experiment occurred mainly from 45 to 90 DAT, and the primary metabolism was modulated by C-P lyase.

Flurtamone and atrazine adsorption to soil was examined using a batch equilibrium method. Flurtamone mobility in packed soil columns under saturated flow conditions was also evaluated. Adsorption was greater for flurtamone than atrazine in the three soils, and the order of adsorption to soil for both herbicides was Greenville sandy clay loam > Cecil loam > Dothan loamy sand. Greater adsorption of each herbicide corresponded to soils with greater organic matter and clay content. The 14C–flurtamone movement under saturated flow conditions in 28–cm soil–packed columns was limited to 16 cm, with no flurtamone leaching from any soil column after the addition of two pore volumes of water. Seventy–five percent of the applied 14C–flurtamone remained in the 0– to 4–cm soil depth in the Greenville sandy clay loam, with less than 5 percent moving to a depth > 4 cm. Flurtamone movement was greater in the Cecil loam and the Dothan loamy sand, with movement in each soil to a depth of 16 and 12 cm, respectively.

Integrated weed management (IWM) decision strategies in herbicide-resistant canola-production systems were assessed for net returns and relative risk. Data from two field experiments conducted during 1998 to 2000 at two locations in Alberta, Canada, were evaluated. A herbicide-based experiment included combinations of herbicide system (glufosinate-, glyphosate-, and imazethapyr-resistant canola varieties), herbicide rate (50 and 100% of recommended dose), and time of weed removal (two-, four-, and six-leaf stages of canola). A seed-based experiment included canola variety (hybrid and open-pollinated), seeding rate (100, 150, and 200 seeds m−2), and time of weed removal (two-, four-, and six-leaf stages of canola). For the herbicide-based experiment, strategies with glyphosate were profitable at Lacombe, but both imazethapyr and glyphosate strategies were profitable at Lethbridge. Weed control at the four-leaf stage was at least as profitable as the two-leaf stage at both sites. For the seed-based experiment, the hybrid was more profitable than the open-pollinated cultivar, seed rates of 100 and 150 seeds m−2 were more profitable than 200 seeds m−2, and weed control at the two- and four-leaf stages was more profitable than at the six-leaf stage. When risk of returns and statistical significance was considered, several strategies were included in the risk-efficient set for risk-averse and risk-neutral attitudes at each location. However, the glyphosate-resistant cultivar, the 50% herbicide rate, and weed control at four-leaf stage were more frequent in the risk-efficient IWM strategy set. The open-pollinated cultivar, 200 seeds m−2 rate, and weed control at the six-leaf stage were less frequent in the set. The risk-efficient sets of IWM strategies were consistent across a range of canola prices.

Research was conducted to characterize the phenology of common lambsquarters growth parameters as influenced by climatic variation among years. Treatments included soybean or corn grown alone, common lambsquarters with soybean or corn, and common lambsquarters grown alone. Common lambsquarters leaf area and plant height phenology differed among years and was variable within treatments. Conversely, crop leaf area and plant height phenology did not differ among years and was less variable within a treatment than common lambsquarters. Weed relative leaf area and relative volume differed among years because of differences in crop and common lambsquarters leaf area and plant height phenology. Differences in common lambsquarters relative leaf area and relative volume among years may explain differences in previously reported crop yield responses to weed infestations between sites and years. Although common lambsquarters relative leaf area and relative volume differed among years, variability as indicated by regression coefficients of determination was also high within year and treatment. Crop leaf area and plant height phenology were well described by regression equations, with r 2 values greater than 0.68. Therefore, low coefficients of determination for relative leaf area and relative volume models were attributed to variability in common lambsquarters within a treatment.

When glyphosate [N-(phosphonomethyl)glycine] at 0.075 kg/ha, DCPA (dimethyl tetrachloroterephthalate) at 10 kg/ha, and H 26905 [O-ethyl-O-(3-methyl-6-nitrophenyl)-N-sec-butyl phosphorothioamidate] at 0.25 and 0.5 kg/ha were sprayed on foliage of alfalfa (Medicago sativa L. ‘Vernal’) on which field dodder (Cuscuta campestris Yunck.) and largeseed dodder (Cuscuta indecora Choisy) were attached and growing vigorously, almost all visible dodder tissue was killed and alfalfa was not injured noticeably. Some dodder recovered from haustoria within the alfalfa stems and from remnants of twined tendrils, but devastation of the alfalfa by uncontrolled dodder was prevented. PP 009 (butyl 2-[4-(5-trifluoromethyl-2-pyridyloxy)phenoxy] propionate), BAS 9052 (2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one) and RO 13-8895 (acetone-O-[D-2-[p-[(α,α,α-trifluoro-p-tolyl)-oxy] phenoxy] propionyl] oxime) at 0.25, 0.50, or 1.0 kg/ha did not control dodder.

On-farm field experiments were conducted in the Piedmont Plateau and Coastal Plain of North Carolina in 1981 and 1982 to investigate the integration of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} with other chemical and cultural weed control tactics into soybean [Glycine max (L.) Merr.] weed management systems. Sethoxydim at 0.2 kg ai/ha provided control of broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash. # BRAPP], large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA], and fall panicum [Panicum dichotomiflorum Michx. # PANDI) equal to control achieved with registered rates of the soil-applied herbicides alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl)acetanilide] and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). Control of broadleaf weed species with the postemergence herbicides bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4-(3H)-one 2,2-dioxide] and acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} equaled or exceeded the control obtained with the soil-applied herbicides linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5-(4H)-one]. Applications of 0.22 kg/ha of sethoxydim 2, 3, 4, and 5 weeks after soybean planting provided season-long control of fall panicum and crabgrass in 1981. In 1982, crabgrass control was 88 to 99% up to 4 weeks after planting. Later applications provided inadequate control of the grass species. Variations in volume and pressure of application had no effect on control of 10-cm goosegrass [Eleusine indica (L.) Gaertn. # ELEIN] or broadleaf signalgrass with 0.2 kg/ha of sethoxydim. Increasing pressure increased control of 30-cm goosegrass and broadleaf signalgrass. Increasing volume increased only control of goosegrass. Bentazon and acifluorfen provided better control of broadleaf weeds when applied early than when applied late. In two of four experiments tank mixtures of sethoxydim and bentazon resulted in an initial decrease in grass control compared to corresponding sequential applications. Soybean yields were comparable, however.

Influence of time of planting and distance from the cotton row of pitted morningglory (Ipomoea lacunosa L.), prickly sida (Sida spinosa L.), and redroot pigweed (Amaranthus retroflexus L.) on yield of seed cotton (Gossypium hirsutum L. ‘Stoneville 213’) was determined on Decatur clay loam during 1975 through 1978. Weed growth was measured in 1977 and 1978. Seeds of the three weed species were planted 15, 30, or 45 cm from the cotton row at time of planting cotton or 4 weeks later. Weeds planted 4 weeks after planting cotton grew significantly less than did weeds planted at the same time as cotton. When planted with cotton, redroot pigweed produced over twice as much fresh weight as did prickly sida or pitted morningglory. The distance that weeds were planted from the cotton row did not affect weed growth in 1978, but did in 1977. The distance that weeds were planted from the cotton row did not affect their competitiveness in any year as measured by yield of cotton. However, in each year, yields of cotton were reduced to a greater extent by weeds planted with cotton than when planted 4 weeks later. In 3 of 4 yr, there were significant differences in competitiveness of each of the three weed species with cotton.

Crop rotation promotes productivity, nutrient cycling, and effective pest management. However, in row-crop systems, rotation is frequently limited to two crops. Adding a third crop, especially a perennial crop, might increase crop-rotation benefits, but concerns about disruption of agricultural and ecological processes preclude grower adoption of a three-crop rotation. The objective of the present research was to determine whether weed seed banks differ between a sod-based rotation (bahiagrass–bahiagrass–peanut–cotton) and a conventional peanut–cotton rotation (peanut–cotton–cotton) and the importance of crop phase in weed seed-bank dynamics in a long-term experiment initiated in 1999 in Florida. Extractable (ESB) and germinable (GSB) seed banks were evaluated at the end of each crop phase in 2012 and 2013, and total weed seed or seedling number, Shannon-Weiner's diversity (H′), richness, and evenness were determined. ESB increased in H′ (36%), richness (29%), and total number of weed seeds (40%) for sod-based compared with conventional rotation, whereas GSB increased 32% in H′, 27% in richness, and 177% in total number of weed seedlings. Crop phase was a determinant factor in the differences between crop rotations. The first year of bahiagrass (B1) exhibited increases in weed seed and seedling number, H′, and richness and had the highest values observed in the sod-based rotation. These increases were transient, and in the second year of bahiagrass (B2), weed numbers and H′ decreased and reached levels equivalent to those in the conventional peanut–cotton rotation. The B1 phase increased the germinable fraction of the seed bank, compared with the other crop phases, but not the total number of weed seeds as determined by ESB. The increases in H′ and richness in bahiagrass phases were mainly due to grass weed species. However, these grass weed species were not associated with peanut and cotton phases of the sod-based rotation. The results of the present study demonstrated that including bahiagrass as a third crop in a peanut–cotton rotation could increase weed community diversity, mainly by favoring increases in richness and diversity, but the structure and characteristics of the rotation would prevent continuous increases in the weed seed bank that could affect the peanut and cotton phases.

Biofumigation is practiced to control soilborne pests and weeds in agronomic fields. The objectives of this research were to assess the dose response of weed seeds to Indian mustard biofumigation and associate responses to seed dormancy state, initial dormancy, and seed parameters. A petri dish biofumigation methodology was developed to expose seeds of common lambsquarters, bird vetch, wild carrot, common ragweed, green foxtail, velvetleaf, hairy galinsoga, and red clover to allelochemicals produced after rehydrating 0 (control), 1.94, 2.90, 5.81, 11.61, and 17.41 mg cm−2 of dried mustard powder. Weed species expressed specific dose responses, estimated ED50, LD50, and maximal mortality. Hairy galinsoga and wild carrot were consistently the most affected by biofumigation, with maximal mortality reaching 97% and 95%, ED50 values for germination were 1.91 and 2.68 mg cm−2 , and LD50 values were 3.31 and 3.69 mg cm−2 of dried mustard tissue, respectively. Initial dormancy was assessed by germination and tetrazolium tests. Seed parameters such as testa thickness, relative weight of the testa, and seed size were measured directly by manual dissection, weighing seed structures, and stereomicroscopic imaging software measurements. Linear regression analyses revealed initial dormancy to be positively related to ED50 and LD50 values with a significant interaction with seed surface and seed width, respectively. Exposure to 5.81 mg cm−2 of dried mustard powder increased common ragweed seed mortality for after-ripened seeds by 293% and by 58% for primary dormant seeds compared with untreated seeds. Mortality of common lambsquarters secondary and primary dormant seeds increased by 730% and 106%, respectively, and for wild carrot by 1,193 and 156%, respectively. Results underline the potential to incorporate biofumigation into weed management programs for repression of susceptible weed species.

Fluazifop-P-butyl, a selective graminicide, has been widely used to control annual grass weeds for more than three decades in Taiwan, and a resistant (R) biotype of goosegrass has consequently appeared. In this study, liquid chromatography/tandem mass spectrometry (LC/MS/MS) was applied to analyze metabolites of fluazifop-P-butyl in a R biotype of goosegrass. Six signals, including mass-to-charge ratios (m/z) 512, 432, 423, 415, 314, and 160, in positive scanning mode, and four signals, including m/z 788, 623, 593, and 162, in negative scanning mode, were found in the metabolites of the R and S biotypes, respectively. All of the signals of these metabolites in the R biotype showed higher intensity than those of the S biotype, except for m/z 162. Based on the molecular weights of the fragments (MS2 signal) from the molecules (MS1 signal) and comparison with the Metabolite Link Metabolomics database, MassBank database, and related references, one reduced form of fluazifop acid, i.e., 2-[4-(5- trifluoromethyl-2-pyridyloxy) phenoxy] propanol (MW 313); two types of intermediates of MW 163, i.e., 5-trifluoromethyl-2-pyridone and 5-trifluoromethyl-2-hydroxypyridine (or 2-hydroxy-5-trifluoromethyl pyridine); and five possible conjugated compounds containing a common core fragment (MW 255) from fluazifop acid were identified. In addition, another compound, likely degraded from one of the five conjugated compounds, was also detected. Accordingly, the metabolic pathway of fluazifop-P-butyl in goosegrass is described in this study. An enzyme kinetic study on glutathione S-transferase showed that the R biotype has higher affinities to the substrates reduced glutathione (GSH) and 1-chloro-2, 4-dinitrobenzene, with S/R Km ratios of 3.0 and 2.4, respectively. No difference in Vmax was found, revealing that the S biotype has a strong ability to bind GSH and herbicide or target molecules and showed susceptibility to fluazifop.

In 1982 and 1983, CGA 82725 {2-propynyl-2-[4-[(3,5-dichloro-2-pyridinyl)oxy] phenoxy] propanoic acid}, fenoxaprop {(±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxyl]propanoic acid}, fluazifop {(±)-2-[4-[[5-trifluoromethyl)-2-pyridinyl] oxy]phenoxy] propanoic acid}, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, and sethoxydim {2-[1-(ethoxyimino-(butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} were evaluated as postemergence treatments for the control of rhizome johnsongrass [Sorghum halepense (L.) Pers. # SORHA] in cotton (Gossypium hirsutum L. ‘Acala SJ-2′). Applications of fluazifop or haloxyfop, and the higher rates of sethoxydim or CGA 82725 or fenoxaprop, controlled 90% or more johnsongrass 20 and 52 weeks after application and prevented cotton yield losses.